avex air training ppl - human performance & limitations

HUMAN

PERFORMANCE

and

LIMITATIONS

AVEX AIR TRAINING

PRIVATE PILOT LICENCE

HUMAN

PERFORMANCE

and

LIMITATIONS

© Avex Air Training (Pty) Limited, 2004. (Reg No 67/00941 {07)

Corner Loper Avenue and Zurich Road Aeroport, Spartan Ext 2 Kempton Park SOUTH AFRICA

S26° 07.21 9 E028o 1 2.41 9

Private Bag X1 0404 EDLEEN, 1 625 Republic of South Africa Tel: (01 1 ) 974·4855 Fax: (01 1 ) 974·651 7 E-Mail: [email protected] www.avexair.com

Product Code: AAT-MED-PPL

First published in South Africa by Avex Air Training 2004 Revised March 2008 Revised August 2008 Revised December 2010 Revised September 201 1

All rights reserved. In terms of the Copyright Act, No 93 of 1 978, no part of these notes may be reproduced or transmitted in any forrn by any rneans, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without the permission in writing of the publisher.

Private Pilat Licence Revision: 12/2010

An Avex Air Training Publication

© A vex Air Training 10/2004

P RIVATE PILOT LICENCE

HUMAN PERFORMANCE CONTENTS

CHAPTER PAGES SUBJECT

(i) - (iv) INDEX

Gl Gl - G2 GLOSSARY

I H - 1-2 THE AVIATION ENVIRONMENT

1 -Q1 QUESTIONS

2 2-1 - 2-7 THE HUMAN MACHINE

2-Q1 - 2-Q2 QUESTIONS

3 3-1 - 3-7 THE LUNGS


4 4-1 - 4-8 THE EARS


5 5-I - 5-5 THE EYES


6 6-1 - 6-3 PRESSURE


7 7-1 - 7-2 ACCELERATION AND VIBRATION

7-Q1 QUESTIONS

8 8-1 - 8-13 FLYING AND HEALTH

8-Q1 QUESTIONS

9 9-1 - 9-8 HUMAN INFORMATION PROCESSING

9-Q1 - 9Q2 QUESTIONS

10 10-1 - 10-6 HUMAN BEHAVIOUR

1 0-Q1 - 1 0-Q2 QUESTIONS

II

Private Pilot Licence Revision: 12/2010

Il-l ANSWERS


INDEX Accommodation ............................................................................................................................. . 5.1 Acute fatigue ................... ... .... ... ..... ...... .... .... ..... ........... .......................................................... ......... 8.4 Acute insomnia .... ..................... ............................................................................................. .......... 8.5 Acute stress ..................................................................................................................................... 8.1 Adaptation ........ ...... . ..... ... ................................................................................................................ 9.3 Alcoho1. .. ... ....................................................................................................................................... 8.8 Alimentary canal .................................................................................... .......... ...... ... ....... .... ... ... ...... 6.1 Alveoli ............. . ... ... .............................. ............................................................................................ 3.1 Amnesia ........................................................................................................................................... 9.5 Ampula ..................................................... ........ . .... . . . . ........... . ..... . . . . .. ........ ............ ........................... .4.4 Anaemia ............................................................................................................................ ........... . ... 2.7 Anaemic hypoxia ..................................... .. .. ....... ... ..... ..... . . ... . . . ...... ........ ..................................... ..... 3.5 Angina ...... . ... . . . . . . ........ ............................................................................................................ .......... 2.6 Angular accelerations ................................................................................. .. ... .... ...... ..... . ... . ....... . .. .4.5 Anoxia ................ .............................................................................................................................. 3.3 Antacids ........................................................... ...... .. ............... ...... ................ . . . . .... .. ... .......... . ........... 8.9 Antidiarrhoeals .... . ... ........ ..... . . . . . ........... . . . . ... ..................................................................................... 8.9 Antihistamines ......................................... ........ ..... ...... ............ ... ............. ... ............. ......................... 8.8 Antispasmodics .. . . . . ....... ...... . ............................. .............................................................................. 8.9 Anxiety ................................................................................................................................. ........ .. .. 8.2 Apnoea .. . . ... .... ...... ...... ..................................................................................................................... 8.6 Arousal ............................................................................................... ...... ..... ........ . ... ...... .... ..... ...... .. 8.2 Arteries ............ ... ... ... ... ........ .. .............. . ............................................................................................ 2.4 Aspirin .......................................................... . . ... . . ... .... . ....... ... ... ...... ... ...... . . . ..... ................................. 8.8 Asthma .... .... . . . .................................................................................................................................. 3.7 Astigmatism .................................................. . .. .. . ... ... .. .. ...... ....... .... . ..... ............ . ... . ...... . ... ... . .... . ..... ... 5.2 Atherosclerosis ............................................................................................................... ... ......... . . . . . 2.5 Atmosphere ........ . ............. . . .......... . . .................. . ..... . . . ..... . .......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .1 Attitudes ..... .................................................................................................................................... 1 0.1 Auditory nerve .. . . . . . ....... ......... ... ... ..... ....... .. ..................................................................................... .4.2 Autokinesis ............................................................................................................................ .......... 5.5 Barotrauma . . . . . . . . . . . . . . .. . . . . . . . . . . . . . ...................................................... . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . ..... . . . . . . 6.1 Behaviour ............................................................................................................................. ... ... .... 1 0.3 Binocular vision . . . . .................................................. ........... ............ . . . . . .............. . ....... . .. . . . . . . . . . . . . . . . . . . . . 5.3 Biological control system ............................................................................................................... 9.2 Blind spot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................ ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 5.2 Blood glucose .. . . . ................ . ....... .. ............ ...................................................................................... 2.2 Blood pressure ................................................................................................................................ 2.3 Body rhythms ........................ .............................................. ................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Boyle's law .. . ................................................................................................................................... 6.1 Brain ................................................................................................................................................. 9.1 Brain stem . .. ........... . .... . ................... ................................................................................................ 9.1 Bronchial tree .................................................................................................................................. 3.1 Bronchitis .......................................................... . ........... ............... .. ...... .. .. ... .. .... ......... .. ......... ... . . . . .... 3. 7 Caffeine ................. .... ........ ... ...... ..... . ...... ............. .......... ....... ... . ........................................................ 8.8 Capillaries ...................................................................................................................... .... ... ...... . .... 2.4 Carbon dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................................. . . . .............. . . . . ....... . . . . . 3.1 Carbon monoxide .... .......... .... ......... ................................................................................................ 3.5 Cardiovascular system .............................................................................. ... . ... ............ .... .... ... ... . .... 2.1 Cataracts . . . . . . . . . . . ...................... ...................... . . ................. . . ... . . .......... . . .. . . ................. . . ....... . .. . . . . . . . . . . . . 5.4 Central nervous system ............... . . ......... ........................................................................................ 2.1 Central vision ..................................................... ................................. ................... ........... . ... ........... 5.2 Cerebrum . . . . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . . .................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Cerebellum ...................................................................................................................................... 9.1 Cerebral cortex ......................................................................................... .. ... ....................... ........... 9.1 Cholera .......................................... ......................................................... ....................................... 8.1 2 Chronic fatigue ..... . ................... ....................................................................................................... 8.4 Chronic insomnia .......................................................................... ............... . .................. . ..... .. . . ...... 8.5 Chronic stress ........ ............................... .................................................................... ...................... 8 .1 Ciliary muscles ................................................................................................................................ 5.1 Circadian dysrhythmia ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Circadian rhythms ........................................................................................................................... 8.6 Clinical insomnia ............................................................................................................................. 8.5 Closed loop system ........................................................................................................................ 9.7 Cochlea ........................................................................................................................................... .4.2



INDEX Page (i)

Coffee .......................................................... .... ... ... ..... ... .......... . .... . .... ..................... ......................... 8.8 Cones ... ............ ................................................................................................................ . ..... ... . .... . 5.2 Colour vision ................................................................................ . ...... . . ........................ ..... .... ......... 5.3 Composition of the atmosphere .............. ... . ... ..... ... ........... . ..... . ..................................................... 1 . 1 Conjunctivitis ......................................................................................... ... ... ............. . ... .... . ... ........... 5.4 Contact lenses ................................................ . ..... ..... .. . ...... . .... . . ..... . ... . . ... ... ... ....... .... ... .......... ......... 5.3 Coriolis effect ....... ..... ... ..... ..... . . ... ..................................... ............... . .............................................. .4.7 Cornea ...................................................................... . ..... .............. ......................... ... ...... . .... ... . . ..... .. 5.1 Coronary artery disease .............................. ..... ...... ..... .... ........... . ... . ....... . ..... ....... . .......................... 2.5 Coronary embolism .. .... ......... . .... ... ... ... . .......... ......... ............ .... ........................................................ 2.5 Coronary thrombosis ............................................. ............ . ........ .... .... ................. . ..... . ... .......... ....... 2.5 Cough medicine .. . ........... . ... ... . . ...... ..... . ... . ....... .................... . ....... ....................... ............................. 8.9 Cupula .... ............ ... ...... ... . . ............ . ...... . ... . ....................................................................... ............ . . . .4.4 Cyanosis ............................................................................................................ .. . ...... . ... .... .... . .... . ... 3.5 Dalton's law ...... ... ..... ... ... . . ...... ......... .... . ........................................................................................... 6.1 Decision making .................................................................................. ... ....... ...... . ...... . ... . ....... . . ... .. 1 0.5 Decompression sickness .... ... ............ . .... ...... . .......... ...... . .......... . ............. ........................................ 6.2 Decongestants ......................................................................... .............. .... ... ... .... ... .... .... .... .... ... . . ... . 8.9 Depth perception .......................... ... ... ... . ... ... . ... ..... ........ .... ....... . ..................................................... 5.3 Diabetes ...... ......................................................................................... ....... .. . .................... ... ..... . . ... . 2.2 Diastolic pressure .. ... ... .... ... ... ....... ....... ... . ... .... ................ ........ ......................................................... 2.3 Divided attention ............................................................................................... ............ .... . .. .. . .. .... . . 9.6 Electrocardiogram (ECG) . ..... ...................... . ... ..... ........ . ....... ... . ... . .... ... .... . ................ ....... ............... 2.4 Elevator illusion .................................................................. ................. . ..... ..... ....... ... .... .... . ... .. ....... . .4.7 Empty field myopia .............. ................. ... ....... ... ........ ..... . ... .... .... . . ............. ..................................... 5.3 Endolymph ... ..... ......... ............................................................................... ............................ . .. ... ... .4.4 Epilepsy ............... . ..... . ... . ............ .... ... .... . .............. ......................................................................... 8.1 1 Episodic memory ................................................... . ................... ................................ . . .. . . ...... . . ....... 9.4 Extrovert .................. .............. ... . ......... .... ................. ...... .......... ..... .................................................. 1 0.1 Eyedrops ........................ . ............................ . ............................... .... .... .... ..... ...................... .... . ........ 8.9 Factual memory .. . ......... ......... . . ... ... ................................................................................................. 9.3 Faints ......................................................... ........... .... ........ ............ ........... ............. ...... .... ........ . . . . . . . 8 .1 1 False horizon .. ..... ............ ............................................................................ ......... ........... ....... . ...... .. 5.4 Fatigue ............ .......... ........... ...... . ....................... ..... ............... . ... .... . ... ........................... .... . .............. 8.4 Flicker vertigo ...... ... ..... .... . ...... ............. ... . ..................................................................................... .. .4.9 Fovea ................................... .... . . .... ........ ........ . ... ..... ... ........ ........ . ..... ... ......................................... .... 5.2 Fugue state ..................................... ....................................................................................... ......... 9.5 Galactic radiation ........................................................ . ......................... ... . ................... .... . ... .. ... . ... .. 1 .2 Gastro-enteritis ...... ................................................................................................................. . . . . ... 8.1 1 Glare .................................................. ...... ........................... .................. . ......... ........ ......... . . ... ......... .. 5.3 Glaucoma ........................ ...... ................ ............. ..... ... ...... ... .... ..... .... ... . ........................................... 5.4 Graveyard spin ......................................................... . ................ . . ...... ......... .......................... ........ .. .4.7 Graveyard spiral .................. . ............. .............. . ..... ........... ......... .......... .... ... ...................... ... .... . ... . .. .4.7 Ground lighting .. .. ......... . .... ...... .... ... ................................. ... . ........................................................... 5.4 Haemoglobin ................................................................. . .................. .... .... . ..... ...... . ... .... .... . ... . . . . . 2.1 /3.1 Hearing loss .............. . ... . .......... ... ... ... .... .... ............. ...... ...... . . ... ... . ........ ................. .......................... .4.2 Heart ................ ..... ... .... ... . ........ . .... ...... ............................................................................................. 2.2 Heart failure ....................................................................................... ...... . . ................. ...... ...... . ..... ... 2.6 Heart rhythm .......................... . . ... ........ ..... .................................. ..................................................... 2.4 Hepatitis ........ .............................................................................................. ........... ........................ 8 .1 2 High blood pressure ............................... .................. ...................... ......... ...... ........ ...... ........ .. . .. . .... . 2.3 Human error and reliability ...... ................................................................................................... .. 1 0.4 Humidity ................................................. ...................... ........................ ....................... .. .............. .... . 1 . 1 Hyperglycaemia ........................................... ................ .............. ..... ... .... ... . ............ . ... ... . ..... ... . ....... . . 2.2 Hypermetropia .................................................................................................... ............................. 5.2 Hypertension ....................................................... ................................ ....... . ..... ........ ....................... 2.3 Hyperventilation ............................ ...................................... ..... .......... .... ... . ................... . ... . . ... . ..... . . .. 3.6 Hypoglycaemia ................................................................................................................................ 2.2 Hypotension ..................................................................................................... ............................... 2.4 Hypoxia ................................................. ......................... . ................... .. ................. . ...... ... . .... ... ..... . . .. 3.3 Hypoxic hypoxia .................................. ............................................................................................ 3.5 Hystotoxic hypoxia ................................................................................................................ .... .. .... 3.5 Incapacitation ......................................... .... ...... ........ ..... .............. . . ... ... . . . . . ... .. ....... ....... . .... . ... ....... . . 8.1 1 Individual differences ....................................................................................................... ............. 1 0.1 Inner ear .................................................. ... .................... ............... .......... ............. ...... . . ....... .. . . .... . . . .4.2 Insidious incapacitation ..... . ..... ... .... ....... . ... .. ...... ........ .. . ... ... .... .... .... . ............................ ................. 8.1 1 lntrovert ............................. ...................................... . ....................... ... . .. ................ . .. ... . ... ........ . ... . . . 1 0.1 Inversion illusion ........ .... . . ... ... ... . ... ... ...... . .......... ..... ........... ... . ... . . .......... .... ................... ...... .............. .4.7 Iris .................................................................................................................................................... 5.1 Jet lag ................. ... ......... . ..... ... . ... ... ... .... .......... ....... ......... ... . ... . ... . .... ...... .................. .......... . .... .... . . ... 8.7



INDEX Page (ii)

Kidneys ............................................................................................................................................ 2.5 Kidney stones .................................................................................................................................. 2.6 Knowledge based behaviour ........................................................................................................ 1 0.4 Landing illusions ............................................................................................................................. 5.5 Lens ................................................................................................................................................. 5.1 Linear acceleration .......................................................................................................................... 4.5 Long term memory ......................................................................................................................... 9.4 Loss of cabin pressure ................................................................................................................... 3.7 Low blood pressure ........................................................................................................................ 2.4 Lungs ............................................................................................................................................... 3.1 Macula ........................................................ .................................................................................... .4.5 Malaria ........................................................................................................................................... 8.12 Memory ............................................................................................................................................ 9.3 Middle ear ...................................................................................................................................... .4.1 Migraine ......................................................................................................................................... 8.1 1 Mind set ........................................................................................................................................... 9.7 Monocular vision ............................................................................................................................. 5.3 Motion sickness .............................................................................................................................. 4.8 Motivation ...................................................................................................................................... 1 0.3 Motor programme ........................................................................................................................... 9.8 Motor nerves ................................................................................................................................... 9.2 Motor skill memory ......................................................................................................................... 9.3 Myopia ............................................................................................................................................. 5.2 Narcolepsy ............................................................................................. .......................................... 8.5 Nausea ............................................................................................................................................. 8.9 Nervous insomnia ............................................................................................................. ..... ......... 8.5 Nervous system .............................................................................................................................. 2.1 Night vision .................................................................................. ......... ........................................... 5.3 Oculogravic illusion ........................................................................................................................ .4.6 Open loop system ......................... ................................................................................................. 9.8 Optic nerve ...................................................................................................................................... 5.2 Orthodox sleep ................................................................................................................................ 8.5 Ossicles ........................................................................................................................................... 4.1 Otolith organs ................................................................................................................................. .4.5 Outer ear ........................................................................................................................................ .4.1 Ozone ............................ .................................................................................................................. 1 . 1 Painkillers ......................................................................................................................................... 8.9 Paradoxical sleep ...................................................... ......................... ............................................. 8.4 Paranasal sinuses ................................................................ ........................................................... 6.2 Partial pressure ..................................................... ................................... ....................................... 3.3 Peripheral nervous system ............................................................................................................. 2.1 Peripheral vision ...................................................................... .................................. ...................... 5.2 Personality ............................. ........................................................................................................ 1 0.1 Personality characteristics ............................................................................................................ 1 0.1 Pilots, drugs and self-medication ................................................................................................... 8.7 Plasma ............................................................................................................................................. 2.1 Platelets ........................................................................................................................................... 2.1 Pleurisy ............................................................................................................................................ 3.7 Presbyopia ....................................................................................................................................... 5.2 Pressure ........................................................................................................................................... 1 .2 Pressure vertigo ........................................................ ..................................................................... .4.9 Pulse rate ........................................................................................................................................ 2.4 Pupil ......................................................................... ........................................................................ 5.1 Radial keratotomy ............... . . . ............. ............................................................................................ 5.4 Radiation .......................................................................................................................................... 1 .2 Red blood cells .............................................................................................................. ................. 2.1 Reflexes ........................................................................................................................................... 9.2 REM sleep ....................................................................................................................................... 8.4 Respiration ....................................................................................................................................... 3.1 Retina ............................................................................................. .................................................. 5.2 Rods ................................................................................................................................................. 5.2 Rule based behaviour ........................................................................................................... . . ...... 1 0.4 Saccule ..... ........................................ . ............................................................................................. .4.5 Selective attention ........................................................................................................................... 9.5 Semantic memory ..................................... ...................................................................................... 9.4 Semi-circular canals ....................................................................................................................... .4.4 Sensitivity .............................................................................................. ........................................... 9.2 Sensory threshold ........................................................................................................................... 9.3 Short-term memory ......................................................................................................................... 9.3 Situational awareness ................................................................................................................... 1 0.5



INDEX Page (iii)

Situational insomnia ........................................................................................................................ 8.5 Skill-based behaviour .................................................................................................................... 1 0.3 Sleep .................................................................................................... ............................................ 8.4 Sleep management ......................................................................................................................... 8.6 Sleep patterns ................................................................................................................................. 8.5 Sleeping problems .......................................................................................................................... 8.5 Solar Radiation ................................................................................................................................ 1 .2 Somnambulism ................................................................................................................................ 8.6 Sound ............................................................................................................................................. .4.3 Spatial disorientation ...................................................................................................................... .4.6 Spatial orientation .......................................................................................................................... .4. 6 Spinal chord .................................................................................................................................... 9 .2 Stages of sleep ............................................................................................................................... 8.4 Stages of stress .............................................................................................................................. 8.2 Stagnant hypoxia ............................................................................................................................ 3.5 Stressors .......................................................................................................................................... 8.1 Stroke .............................................................................................................................................. 2.6 Sty .................................................................................................................................................... 5.4 Sudden incapacitation .................................................................................................................. 8.1 1 Survival .......................................................................................................................................... 8.1 2 Systolic pressure ............................................................................................................................. 2.3 Teeth ................................................................................................................................................ 6.1 The Jeans ........................................................................................................................................ .4.6 Time of useful consciousness ........................................................................................................ 3.5 Tobacco ........................................................................................................................................... 8.8 Toxic materials .............................................................................................................................. 8.1 0 Trachea ............................................................................................................................................ 3.1 Typhoid .......................................................................................................................................... 8.1 2 Utricle .............................................................................................................................................. .4.5 Veins ................................................................................................................................................ 2.4 Ventilation ........................................................................................................................................ 3.1 Vertigo ................................................................................................................................... ..... ..... .4.9 Vestibular apparatus ...................................................................................................................... .4.2 Vestibular system ........................................................................................................................... .4.4 Vestibule .......................................................................................................................................... 4.5 Visual acuity .................................................. .................................................................................. 5.2 White Blood cells ............................................................................................................................ 2.1 Working memory ............................................................................................................................. 9 .3 Yellow fever ..... .............................................................................................................................. 8.12 Zeitgebers ........................................................................................................................................ 8.6



INDEX Page (iv)

GLOSSARY ALVEOLI

GLOSSARY Page G-1

Terminal, minute air sacs in the lungs through which oxygen passes into the blood.

ARTERY

A tube of muscle and connective tissue fibres which distributes blood from the heart to the capillaries.

ANTIHISTAMINES

A group of drugs used to treat allergic conditions, such as hay-fever, a side effect of which is drowsiness.

BAROTRAUMA

Damage/pain caused by the expansion or contraction of a gas trapped within the body, owing to pressure changes.

CAPILLARY

A minute vessel network connecting an artery and a vein.

CARDIOVASCULAR

Concerning the heart and blood vessels.

CELL

A microscopic mass of protoplasm (organic compound), including a nucleus, of which tissues are made.

COCHLEA

The spiral canal of the inner ear. (Hearing organ).

CYANOSIS

A bluish appearance of the skin and mucous membranes, caused by deficient oxygenation of the blood.

EXPIRATION

Breathing out.

HAEMOGLOBIN

The colouring matter of the red blood corpuscles. It consists of protein and iron and has a strong affinity for oxygen.

HYPERTENSION

Raised blood pressure.

HYPOTENSION

Low blood pressure.

INSPIRATION

Breathing in.

LEFT ATRIUM

The left upper chamber of the heart.



LEFT VENTRICLE

The left lower chamber of the heart.

LUMEN

The space inside a tube or organ.

MUCUS

A sticky secretion from mucus membranes.

OSSICLE

A small bone, such as those in the middle ear known as the malleus, incus and stapes.

OTOLITH

GLOSSARY Page G-2

A hard structure at the base of the semi-circular canals, containing delicate sacs known as the utricle and the saccule.

PATHOLOGY

Disease, and the change in structure and function it causes.

PHYSIOLOGY

The functions of living bodies or organs.

RESPIRATION

The gaseous interchange between the blood and the tissues.

TISSUE

A mass of cells an connective tissue, forming one of the organs of which the body is composed.

TRACHEA

The wind pipe; a tube extending from the larynx (voice organ) and separating into two branches known as bronchi before entering the lungs.

VASCULAR

Relating to, or consisting of vessels.

VEIN

A vessel carrying blood from the capillaries back to the heart.

VENTILATION

The gaseous interchange between the lungs and the atmosphere.

VERTIGO

A feeling of rotation, associated with the vestibular function of the ear.

VESTIBULAR

The function of the semi-circular canals concerned with balance and equilibrium.


© A vex Air Training 1 0/2004

CHAPTER 1 THE AVIATION ENVIRONMENT Page 1-1

THE AVIATION ENVIRONMENT A. INTRODUCTION

During the period of human evolution, biological development enabled the human being to adapt to a variety of environmental variables such as temperature, humidity and land based altitude where the air is relatively dense and there is sufficient oxygen to sustain life. With the advent of aviation, and in particular high altitude and high speed flight, the human body now has to adapt fairly quickly to a rapidly changing environment, and one where decreased air density means less oxygen and lower temperatures. It is, in effect, an alien environment. From the pilots point of view, then, it becomes important to understand the limitations of the human body and the methods and procedures used to prevent damage to what is a fairly delicate machine.

B. THE ATMOSPHERE

The atmosphere as a subject is covered in greater detail in Meteorology. However, a brief summary is pertinent here as a prelude to its effect on the human body.

1 . STRUCTURE OF THE ATMOSPHERE

The atmosphere comprises three main sections, in ascending order these are: the Troposphere, the Stratosphere and the Ionosphere. Of these, the troposphere is the more important since it is within this area, which extends from sea level to approximately 60 000 ft, that weather occurs and humans live and now fly.

2. COMPOSITION

The atmosphere is made up of many gases, the two most predominant being Oxygen (approximately 21 %) and Nitrogen (approximately 78%). From the human perspective it is oxygen which is the essential element, since it is life sustaining. Oxygen is absorbed through the lungs and distributed by the blood to the various organs of the body where it is used to burn glucose and release energy.

3. TEMPERATURE

One of the characteristics of the atmosphere is the decrease in temperature with altitude, which averages about 2°C per 1 000 ft. Variations in this lapse rate are partly responsible for the creation of weather. At very high altitudes the air is very cold, around -50°C. This variation in temperature, from warm to extremely cold is of significance to the pilot who, being human, requires an internal temperature of around 36SC or 98°F, to be able to operate normally.

4. HUMIDITY

Water vapour is present in variable amounts throughout the atmosphere. It is variable as a result of temperature: warm air can hold more water vapour than cold air. At high altitudes the cold, dry air is compressed as a function of the jet engine to provide air for humans to breathe. Despite some warming in the process, the air remains fairly dry. As part of the breathing process, water vapour is expelled from the body, which, in the dry air of the aircraft may result in a local drying of mucous membranes and present symptoms of dehydration. A normally hydrated person starting a flight will only require a slightly increased fluid intake. It should be noted that alcoholic beverages are not the ideal fluids since alcohol has a diuretic effect, ie it encourages the kidneys to lose excessive water.

5. OZONE

Ozone (03), a chemically altered form of oxygen (02), is created when oxygen is subjected to electrical discharges, such as lightning. It is very poisonous, and even if very low concentrations are inhaled it can damage the very delicate linings of the lungs and air passages.

Below 40 000 ft there is very little ozone present, but it increases significantly towards the lower stratosphere. Concentrations of ozone also increase in the polar regions. It is not considered a serious threat to crew or passengers in pressurised aircraft. Greatest exposure would occur in flights over the poles, or in supersonic aircraft which operate higher than normal commercial jet aircraft. However, during the compression process for pressurisation external air is warmed which breaks down the ozone into oxygen. Catalytic filters may also be installed in aircraft which continually operate in an ozone environment.



THE AVIATION ENVIRONMENT Page 1-2

The presence of ozone in the atmosphere serves as a barrier, preventing a large proportion of the damaging ultra violet radiation of the sun from reaching the earth's surface.

6. PRESSURE

Air pressure is the force exerted per unit area by a column of air as high as the atmosphere. It can be expressed in a number of ways, for example in pounds per square inch (lb/sq inch). or in inches of mercury (Hg). The metric system, more often being used in aviation, expresses pressure in grams per cubic centimetre, or more commonly in Hectopascals (hPa).

·sea level pressure is expressed as 1 01 3.25 hPa, or 1 4.7 lb/sq inch, or 29.92" Hg.

As altitude is gained the length of the column of air reduces and, logically, so does the pressure it exerts at a particular altitude. Under standard conditions (ISA), a layer of air 1 hPa in depth equals 27.92 feet at mean sea level. Traditionally this is rounded off to 30 feet. However, at 20 000 ft 1 hPa equals 47 feet, at 40 000 feet it equals 98.91 feet, whilst at 60 000 feet it equals 1 60 feet. This reduction in pressure with altitude can have dire consequences for the human body. Without oxygen the body cannot survive; pressure causes oxygen in the lungs to diffuse into the bloodstream. A reduction in pressure means that fewer oxygen molecules are able to enter the bloodstream, a problem which is compounded by the fact that at altitude the air is less dense. Without pressurisation or supplementary oxygen the body cannot survive at altitude. See also Chapter 3, The Lungs and Chapter 6, Pressure.

7. RADIATION

Radiation, in the form of X rays, has long been used for the diagnosis of bone and other injuries as well as the effective treatment of some types of cancer. However, the negative effects of radiation are possible damage to the genetic material, (the blueprint), of living cells which may cause replicated cells to be abnormal. In order to determine the advisability of radiation treatment, and the probable effects of radiation damage as opposed to the benefits of the treatment, certain standards have been established, known as the rad and the rem.

A rad is a measure of the actual amount of ionising radiation absorbed by living tissues. Exposure to 800 or more rads is fatal to humans. Exposure to 450 rads causes the deaths of roughly half of the people exposed. A few people are unable to survive exposure to 200 rads. At doses of 50 rads or less there are no immediate outward signs of illness, but some parts of the body such as germ cells, vital to sexual reproduction, are genetically damaged.

A rem is the amount of radiation necessary to cause the same biological effect in humans as one rad of X rays. Most people are thought to receive about 0.3 rem of natural radiation each year, whilst the International Committee on Radiation Protection recommends a maximum of 0.5 rem per year for the general public, well below the accepted maximum of 5.0 rem per year for radiation workers.

Cosmic radiation comprises two parts:

GALACTIC RADIATION.

This comprises short wave electromagnetic waves originating from outside the solar system. These high energy particles are deflected by the earth's magnetic field providing maximum protection in the equatorial regions and minimum at the poles. Additional protection is achieved through stratospheric absorption, so that on the ground the radiation is much less than at altitude. Logically, then, the higher we fly the greater the exposure to radiation. In the early days of the supersonic Concorde, which operates at altitudes far in excess of subsonic jet aircraft, cabin crew wore dosimeter badges to measure the amount of radiation and the aircraft was also fitted with radiation alarm signals. Whilst the dosimeter badges have been done away with, the aircraft still contain radiation warning devices. The South African Civil Aviation Regulations (CAR), require that any aircraft operating in excess of 49 000 ft be equipped with a cosmic radiation detection device.

SOLAR RADIATION/ULTRAVIOLET (UV) LIGHT RAYS.

This longer wavelength radiation originates from the sun and is necessary for the production of vitamin D, essential for the maintenance of bone development in the human body. Exposure to UV radiation produces melanin in skin cells creating a darkening in skin colour, or the suntan. Over exposure can cause a genetic mutation in skin cells and skin cancer. Natural protection from UV rays is provided by the ozone layer, whilst people who spend a great deal of time in direct sunlight are encouraged to use suntan lotions containing high UV blocking agents.



QUESTIONS

(ANSWERS ON PAGE 1 1 -1 )

1 . 21 % of the volume of the atmosphere is made up of:

(a) oxygen, (b) nitrogen, (c) carbon dioxide, (d) ozone.

2. 78% of the volume of the atmosphere is made up of:

(a) carbon dioxide, (b) oxygen, (c) water vapour, (d) nitrogen.

THE AVIATION ENVIRONMENT • QUESTIONS Page 1 -Q1

3. The percentage composition of the gases which make up the atmosphere is constant:

(a) only at sea level, (b) only when ISA standards prevail, (c) throughout the atmosphere irrespective of altitude, (d) only at sea level along the equator.

4. With regard to the structure of the atmosphere:

(a) the stratosphere extends from sea level to approximately 60 000 ft, (b) the troposphere extends from sea level to approximately 60 000 ft, (c) the ascending order is stratosphere, troposphere and ionosphere, (d) the ascending order is troposphere, ionosphere and stratosphere.

5. The symbol for oxygen is:


©A vex Air Training 10/2004

CHAPTER 2 THE HUMAN MACHINE Page 2-1

THE HUMAN MACHINE A. INTRODUCTION

The human body, like a complex machine, has a number of components which combine to make it work. For the machine to function at its best all components must be in good condition. The same applies to the human body. The purpose of this chapter is to give the student an overview of the parts of the body which relate to the working of those systems which are, perhaps, more pertinent to the pilot and which are covered more fully in the various chapters of this book.

B. THE NERVOUS SYSTEM

The nervous system is the "electronics" of the machine and the brain is the computer, sending messages to and receiving them from the various components. The human nervous system consists of two distinct parts:

1 . The Central Nervous System comprising the brain and the spinal chord. 2. The Peripheral Nervous System which connects the central nervous system to the body organ sys

tems.

Not all of the body's components need to be consciously told what to do. The nervous system allows for voluntary action, ie the brain telling muscles and limbs to move, and involuntary action, ie the heart rate, blinking of the eyes, sweating and working of the gastro-intestinal tract are accomplished automatically through the autonomic nervous system.

C. THE CARDIOVASCULAR SYSTEM

1 . BLOOD

In order for the body to work it requires both nutrients and oxygen. These are transported around the body by the blood which also removes certain waste material, e.g. carbon dioxide. Blood comprises two parts: plasma and blood cells. The average mature adult will have between 3.5 - 5 litres of blood.

PLASMA

This is the medium through which the cells are transported around the body. It is a yellowish coloured fluid comprising approximately 90% water. It also contains thousands of different substances, including proteins, vitamins, glucose, salts, hormones, antibodies and wastes.

BLOOD CELLS

(a) RED BLOOD CELLS

These contain the iron-rich protein haemoglobin, which is a complex and very efficient system used to transport oxygen around the body. It is capable of absorbing large quantities of oxygen, holding the molecules until it reaches an area of low oxygen levels where the oxygen is then released into the tissues. Carbon dioxide is also attracted by the red blood cells for transportation to the lungs and removal from the body. See Chapter 3, The Lungs. Red blood cells are formed in the red marrow of flat bones such as the ribs, vertebrae and skull as well as the ends of long bones found, for example, in the legs. The normal count in an adult is 5,000,000 red blood cells per cubic millimetre (c.mm) of whole blood.

(b) WHITE BLOOD CELLS

These are the part of the body's defence system which produce blood protein antibodies which in turn are transported around the body to fight infection and disease. There are various types of white cells, some of which are formed in the bone marrow, others by the spleen and lymph glands. The normal count per adult is between 5,000 and 1 0,000 per c.mm of whole blood.

(c) PLATELETS

These are the key ingredient in the formation of blood clots. Where a blood vessel has been cut or damaged, platelets stick to the edges of the wound forming a clot or plug which will prevent further blood loss. These are also formed in the bone marrow. The normal count per adult is 200,000 per c.mm of whole blood.



BLOOD SUGAR (Blood Glucose)

THE HUMAN MACHINE Page 2-2

The bulk of the energy required by the body for everyday activities is obtained from carbohydrates, the source of which includes bread, cereals, rice, potatoes, pasta and sugar. These carbohydrates are digested and converted to glucose by the digestive enzymes in the gastro-intestinal tract. The amount of glucose present in the blood is critical, since the brain is particularly sensitive to incorrect amounts. Glucose is stored in the body - in the liver and muscles - as a substance called Glycogen, which is easily reconverted into glucose as and when required by the body. Because diets vary and can include fairly large amounts of sugar, it is necessary for the body to be able to control the levels of blood glucose. This is achieved through two hormones called Insulin and Glucagon. Insulin, which is secreted by the pancreas, is the more important of the two since its function is to chemically alter glucose into the form in which it is stored in the liver. As blood glucose levels fall glucagon is released which allows the stored glucose to be released back into the blood-stream. There are two conditions which are of importance to us.

(a) HYPERGLYCAEMIA (EXCESS BLOOD GLUCOSE)

A deficiency of insulin leads to a disease called diabetes, a situation where excess glucose is not stored but builds up in the blood until a certain level is reached, at which point the kidneys will start to vent the excess glucose into the urine. This function involves the elimination of more water from the body than is normal, and excessive thirst is also an indication of diabetes. The presence of glucose in the urine, being as it is a clear indication of diabetes and, therefore, incorrect blood glucose levels, explains the importance of the urine test in aviation medical examinations. Injections of insulin are able to maintain the blood glucose at the correct level. Consistently high blood glucose levels may ultimately effect body tissues, but the more immediate effect on the brain is of significant importance. High blood glucose levels can lead to behavioural changes which can be mistaken for acute alcoholism.

(b) HYPOGLYCAEMIA (LOW BLOOD GLUCOSE)

This is a temporary condition which can be found in diabetics and non-diabetics. In the case of diabetics it could be as a result of an overdose of insulin due to a tendency to overdo rather than neglect their medication. The symptoms of low blood glucose include dizziness, headache, stomach pains and shaking. This situation can be easily resolved by restoring the blood glucose level by taking glucose or sugar through the mouth. In the event that the person has already entered a coma, glucagon can be injected directly into the blood-stream to energise the glucose reserves from the liver. By not eating well or regularly, non-diabetics may expose themselves to the same symptoms. Recovery is easily achieved simply by eating something. This emphasises the importance of not flying on an empty stomach.

2. THE HEART

The circulation of the blood throughout the body, via a system of blood vessels comprising arteries, veins and capillaries, is achieved by a fist-sized, hollow, muscular pump known as the heart. The heart comprises four chambers; two suction chambers or atrium, and two discharge chambers known as ventricles. Oxygen rich blood is drawn from the lungs through the pulmonary veins by the "sucking" action of the /eft atrium, from the left atrium it passes through a one-way valve, called the bicuspid or mitral valve, to the /eft ventricle. From here it is pumped through another one-way valve - the aortic valve - into the main artery, or aorta, which carries the blood to the upper and lower body. Along the way, oxygen is discharged and replaced by carbon dioxide. The blood is then routed via upper body veins (superior vena cava) and lower body veins (inferior vena cava) to the right atrium of the heart where it passes through a one-way valve, called the tricuspid valve, to the right ventricle which pumps it through another one-way valve - the pulmonary valve - back to the lungs via the pulmonary artery.



Right Atrium

Superior Vena Cava

Vena

Tricuspid Valve

Aorta

Right Ventricle


Pulmonary Veins

Aortic :__ ___ Valve

;----_ Mitral Valve

Left Ventricle

- De-oxygenated blood

- Oxygenated blood

Figure 2-1: The Heart

With regard to normal heart operation, three items may be considered:

(a) BLOOD PRESSURE

This force, exerted by the blood against the walls of the main arteries, is what keeps the blood circulating around the body. Blood pressure has a high and a low point. As the left and right ventricle contract, the pressure will be at it's highest and this is referred to as the systolic pressure. As the chambers relax and refil l with blood the pressure is at it's lowest and this is known as the diastolic pressure. These pressures vary from individual to individual, but a typical figure for a reasonably healthy young adult would be 1 20 mm Hg (millimetres of Mercury) -systolic, and 70 mm Hg - diastolic. In medical terms this is written as 1 20/70. Blood pressure can be used as a measure of a persons health and as most pilots already know, forms a very important part of the aviation medical examination. Dangers are inherent in both high and low blood pressure. Normal blood pressure is dependant on several items, such as the strength of the heart, elasticity of the artery walls, volume and consistency of the blood and the efficiency of the heart valves (no leaks).

HIGH BLOOD PRESSURE (HYPERTENSION)

High blood pressure (hypertension) may be influenced by the following factors:

(i) overweight - a larger mass requires a greater circulation, placing a greater burden on the heart to deliver blood throughout the body;

(ii) smoking - heavy smoking causes the blood vessels to become constricted forcing the heart to pump harder to get the blood through. See a/so Hypoxia (Chapter 4) ;

(iii) being unfit; (iv) emotional state of mind; (v) kidney or heart disease; (vi) genetic; (vii) diet - particularly with regard to an excessive intake of salt, which is utilised by the

body to regulate water retention in the tissues. Too little salt will not allow the body to retain water and it will be excreted. Excessive salt intake will result in too much water being retained in both the tissues and the blood, in the case of the latter the heart will have to work harder to move the greater volume.

Continued long-term high blood pressure may create a situation where a weak point in an artery balloons out. This is known as an aneurysm, a potentially life-threatening condition should the artery wall break, releasing large amounts of blood into the surrounding tissue and causing such a substantial drop in blood pressure, that death results. Other reactions




to sustained high blood pressure include heart attacks, strokes and damaged blood vessels in the eyes and kidneys.

LOW BLOOD PRESSURE (HYPOTENSION)

Unlike high blood pressure, low blood pressure (hypotension) is extremely rare and is seldom a serious or life threatening concern. It may lead to dizziness or even fainting.

(b) PULSE RATE

Blood pressure should not be confused with pulse rate. The pulse rate is the rate at which the heart beats - a function of physical condition. The systematic contraction and relaxation of the heart muscle creates a pressure pulse which may be experienced at various places on the body and is commonly used by medical personnel to assess the well-being of a patient. It is most noticeable in the wrist and the side of the neck. A normal pulse rate for a person at rest would be between 60 and 80 beats per minute. Running, brisk walking or for that matter any form of exercise can temporarily increase the pulse rate, which will return to normal after a rest period. A very fit person may have a very low pulse rate because regular exercise has made the heart more efficient. Hormones, fever and emotional disturbances may also increase the pulse rate. Some medications may increase or decrease the pulse rate, which in turn can adversely affect pilot performance.

(c) RHYTHM

The regular beat of the heart, or the rhythm, is achieved by small electrical impulses which cause the muscle fibres of the upper heart chambers (left and right atrium) to contract. This action forces blood into the lower chambers (left and right ventricles) where the same electrical impulse, now slightly delayed, causes these chambers to contract, squeezing the blood and increasing its pressure for discharge into the arterial system. For the rhythm to remain constant the electrical impulses must remain consistent. It should be remembered that the brain monitors these electrical impulses through the autonomic nervous system, but it does not generate them. The heart contains a special area of tissue in the upper chamber which acts as a natural pacemaker. Failure of this natural pacemaker can be controlled by various drugs or an artificial pacemaker, either inserted by a surgeon, or worn externally. The very fact that electrical impulses control the rhythm of the heart makes it very easy for modern science to monitor its correct functioning. An electrocardiograph detects these impulses and produces a tracing known as an electrocardiogram, or EGG.

3. CIRCULATION

BLOOD VESSELS

The vascular system is the term given to the network of arteries, veins and capillaries which transports blood throughout the body.

ARTERIES

Arteries are fairly thick walled, elastic vessels which transport blood under pressure away from the heart. The main artery is known as the aorta and leads directly away from the left ventricle forming part of the systemic circulation - the delivery of oxygen-laden blood into the tissues. On its return into the right ventricle, the blood is pumped back to the lungs via the pulmonary artery, part of a second system - the pulmonary system - which delivers the blood into capillaries in the lungs. It is here that the exchange of carbon dioxide (exhaled) and oxygen (inhaled) takes place. See Chapter 3.

VEINS

The veins have thinner, less flexible walls than those of the arteries due to the fact that the blood pressure in them is less. They also contain a system of one way valves to prevent a reverse flow of blood. They are responsible for transporting the blood back to the heart.

CAPILLARIES

These are the smallest of the blood vessels and are present in the tissues. Their very fine composition is such that oxygen is able to pass through the membrane into the tissue and waste matter in the opposite direction to be transported away for removal from the body either through the bladder as urine, or through the lungs as carbon dioxide.



THE KIDNEYS


The kidneys are a pair of bean-shaped organs located at the rear of the abdominal cavity that fulfil an essential role in the circulatory system. They are both excretory and regulatory organs in that they filter the blood removing from it any waste material, at the same time regulating the body's fluid balance. Blood enters the kidneys through the renal artery which divides into smaller branches ending in a microscopic structure called a nephron, a part of which contains a filter. There are approximately one million of them in each kidney. Within the nephron harmful or waste substances are separated and routed via the ureter to the bladder for removal from the body. Useful and now balanced substances are reabsorbed into the capillaries and veins and returned to the body via the renal vein. The total volume of the body's blood is cleaned in this way every 50 minutes, which means that between 1 50 and 1 80 litres of blood pass through the kidneys every day.

Renal Vein

Figure 2-2: The Kidney

D. DISORDERS, DISEASE AND ILLNESS

1 . CORONARY ARTERY DISEASE

Renal Artery

Ureter

Heart disease is currently the most likely cause of death or disability in the more industrialised countries, with coronary artery disease being the most common one.

The coronary arteries are two arteries that branch off from the aorta to provide the heart muscle with oxygenated blood. Should one of these arteries become blocked part of the heart will be deprived of blood and die resulting in a heart attack, or myocardial infarction.

Coronary artery disease is most often caused by atherosclerosis, a condition in which fatty deposits, called plaque, become attached to the inner lining of the artery causing it to become narrower and less flexible than it was. As this mass grows it may become hard and chalky, narrowing the artery and restricting the volume of blood it can carry. These clogged areas become ideal sites for the formation of stationary blood clots, which may ultimately shut off the flow of blood completely, a condition called a coronary thrombosis. A condition in which the blockage is caused by a blood clot which moves through the artery and becomes lodged in an area already narrowed is called a coronary embolism. See Figure 2-3.



Artherosclerosis

Figure 2-3: Coronary Artery Disease


Symptoms of a coronary thrombosis are sudden and severe chest pains followed by collapse and possible heart arrest (death}. Considered the curse of civilised society, coronary artery disease can also be hereditary, is influenced by age, diet and habits. Chronic high blood pressure, obesity, lack of exercise, stress and diabetes will contribute, as will foods high in animal fats and smoking.

2. HEART FAILURE

Perhaps the most important heart chamber is the left ventricle. It has considerable muscle mass as it has to pump newly oxygenated blood to the rest of the body. If the left ventricle is damaged it will be unable to meet these demands and will begin to fail. No longer able to cope with the blood being pumped to it from the lungs via the left atrium, pressure begins to build up back through the pulmonary vein into the lungs where it causes congestion. This can result in breathlessness and coughing, the sputum ejected in the process may be pink from blood staining.

3. ANGINA

As a muscle, the heart must have its own supply of blood in order to function efficiently. As the coronary arteries gradually become blocked the heart may well cope in normal circumstances but if, perhaps through exertion, more is effort is demanded from the heart the blood supply may be insufficient resulting in oxygen starvation and a resultant pain in the chest, called angina (muscle cramp}. Unlike the coronary thrombosis, the artery is not completely blocked, it is just sufficiently restricted to prevent a full flow of blood. Also unlike the coronary thrombosis, the pain comes on slowly and not suddenly and whilst normally felt in the chest it can occur anywhere from the lower jaw to the ribs, spreading to the arms or the back and is often accompanied by dizziness, breathlessness and a pale complexion. Regular sufferers use glyceryl trinitrate tablets to relieve the problem.

4. STROKE

A stroke is the term used to describe the effects of a sudden interruption in the supply of blood to the brain as a result of a ruptured blood vessel or a blocked artery. Brain cells which are thus deprived of oxygen either stop functioning or, if deprived for a prolonged period, actually die resulting in the failure of those parts of the body controlled by the affected brain cells. The severity of strokes vary depending on the length of blood deprivation. A short period of reduced blow flow may result in slurred speech, weakness of a hand or foot and blurred or double vision, all of which disappear within a few hours. Longer interruptions of blood flow produce a sudden headache followed by blackout and some permanent but mild dysfunction. A severe stroke results in loss of memory, deterioration of balance, paralysis on one or even both sides of the body and changes in emotional behaviour. The causes of a stroke include high blood pressure, obesity, diabetes, heavy smoking and stress.

5. KIDNEY STONES

Kidney stones, which are crystals usually derived from calcium in the urine, can vary in size from minute enough to pass through the urinary system, to as large as 25 mm in diameter. Gout sufferers may also form stones made of uric acid. The causes vary from hereditary to dehydration and lack of exercise. The predominant symptom is pain in the affected kidney, which my become particularly severe. The cure may vary depending on the type of stone. Those made from uric acid can be dissolved with a solution of sodium bicarbonate, a method which does not work with stones made from calcium. These can be broken down into smaller particles using ultra-sonic waves and easily




passed in the urine. In extreme cases urgent surgery will be necessary to remove the stone before it can damage the kidney. Prevention is most simply achieved by sufficient intake of fluids.

6. ANAEMIA

This is not strictly a disease, but rather a condition. It describes a deficiency in the number of red blood cells or the amount of haemoglobin that they contain and as such is considered a symptom of one of several problems, some of which may be common and therefore easily treated whilst others may be rare and even fatal. The end result is that the body does not obtain sufficient oxygen from the blood which reduces its efficiency and may result in a feeling of weakness or tiredness, breathless and even fainting following exercise. The most common form is iron deficiency anaemia, a condition in which the body is unable to produce sufficient haemoglobin. Remember that it is this iron-rich protein that is responsible for absorbing oxygen from the lungs and transporting it around the body. This condition is easily treated with iron supplements. See also Chapter 3, Anaemic Hypoxia.



QUESTIONS


THE HUMAN MACHINE • QUESTIONS Page 2-01

1 . Haemoglobin, a protein molecule found in the red blood cells:

(a) is a transport molecule for oxygen from the lungs to the tissue cells, (b) acts as a "breathing drive" for the brain, (c) acts as a molecule splitter, by breaking down carbon dioxide in the blood to carbon and oxygen, (d) plays a key role in the formation of blood clots.

2. Anaemia is a condition in which:

(a) there is a decrease in the amount of haemoglobin in the red blood cells, (b) the heart is unable to pump sufficient blood to the lungs to collect oxygen, (c) there is a restriction in the form of a blood clot in a coronary artery, (d) there is a decrease in the amount of haemoglobin in the white blood cells.

3. The part of the body's defence system which produces blood protein antibodies which are transported around the body to fight infection and disease are called:

(a) platelets, (b) white blood cells, (c) red blood cells, (d) haemoglobin.

4. The term systolic is used to indicate that:

(a) blood pressure is at its lowest level, (b) blood pressure is at its highest level, (c) blood pressure is normal, (d) the pulse rate is very low.

5. Long term high blood pressure may lead to:

(a) a decrease in the pulse rate, (b) an increased pulse rate, (c) an increase in the heart rhythm, (d) an aneurysm.

6. Sudden and severe chest pains, following which the victim collapses are symptoms of:

(a) angina, (b) coronary thrombosis, (c) an aneurysm, (d) anaemia.

7. Low blood pressure or hypotension, may lead to:

(a) a heart attack, (b) an aneurysm, (c) dizziness or fainting, (d) an increase in the heart rhythm.

8. Blood pressure is:

(a) the force exerted by the blood against the walls of the main arteries, (b) the rate at which the heart beats, (c) responsible for the regular beating of the heart, (d) measured by the number of beats per minute.



9. Platelets are the blood cells which:

(a) fight infection and disease, (b) play a key role in the formation of blood clots, (c) make up the bulk of blood plasma, (d) carry oxygen around the body.

1 0. Glucose is stored:

(a) in the liver as insulin, (b) in the liver as glucagon, (c) in the liver as glycogen, (d) in the pancreas as insulin.

THE HUMAN MACHINE - QUESTIONS Page 2-02

1 1 . Non-diabetics can also suffer from low blood glucose. The symptoms, which include dizziness and shaking, can be corrected:

(a) by not eating before flying, (b) by eating regularly, (c) only by having an insulin injection, (d) by drinking more water.

1 2. Fainting is a condition which causes a loss of consciousness due to:

(a) a reduction in the supply of blood to the brain, (b) high blood sugar, (c) high blood pressure, (d) a high pulse rate.

1 3. After donating blood a pilot may not fly for a period of:

(a) 48 hours, (b) 36 hours, (c) 24 hours, (d) 72 hours.

14. The term diastolic is used to indicate that:

(a) blood pressure is at its lowest level, (b) blood pressure is at its highest level, (c) blood pressure is normal, (d) the pulse rate is very high.

1 5. Oxygen rich blood is drawn from the lungs through the pulmonary veins by a chamber in the heart called the:

(a) left ventricle, (b) right ventricle, (c) right atrium, (d) left atrium.

1 6. The left ventricle of the heart is responsible for:

(a) pumping de-oxygenated blood back to the lungs, (b) drawing oxygenated blood from the lungs to the heart, (c) pumping oxygenated blood around the body, (d) drawing de-oxygenated blood back to the heart,



CHAPTER 3

A. INTRODUCTION

THE LUNGS

THE LUNGS Page 3-1

In order to understand the effects of flying on our performance, it is first necessary to review various aspects of the operation, l imitation and requirements of the human body. Not the least of which is its requirement for oxygen.

B. OXYGEN AND ITS UTILIZATION

From the study of Meteorology, we are aware of the structure and composition of the atmosphere in respect of the various gases present. Of prime importance to the human being is the volume of oxygen, approximately 21%, without which we cannot live. Of significance to the pilot, is the changing pressure with altitude, and its effect on our ability to breathe and thus extract the required amount of oxygen. In this regard, the gas laws which are pertinent to the pilot are Boyle's law, which states that for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume, and Dalton's Law of Partial Pressure which states that in a mixture of gases, the pressure exerted by one of the gases is the same as it would exert if it alone occupied the same volume. From this statement it is possible to determine the partial pressure of oxygen at any altitude simply because the pressure at a particular altitude can be measured and the proportion of oxygen in the atmosphere is constant. The significance of this law will become apparent later.

The chemical reaction between the food we eat, and the oxygen we breathe creates the energy we require to live. The by-product of this process is carbon dioxide and whilst the human body is able to retain large amounts of it, it is incapable of storing large quantities of oxygen. Thus, there is not only a constant demand for supplies of oxygen, but also a need to remove the carbon dioxide. This gaseous exchange is achieved by ventilation or breathing. The transportation of these gases is achieved via the blood and the exchange is carried out in the lungs (respiration).

C. THE LUNGS

The function of the lungs is to allow oxygen to enter, and carbon dioxide to exit, the blood stream. A combination of the outward movement of the chest wall and the downward movement of the diaphragm creates a decrease in pressure inside the chest, with the result that air is then sucked into the lungs. By relaxing the chest wall and diaphragm, air is expelled from the lungs.

-BJ"Onchi.al Tube

Left tung

Ribs

Diaphragm

Figure 3-1: The Lungs

The inhaled air flows through the trachea to the bronchial tree, which consists of ever dividing branches similar in fact to a tree. At the end of these passageways are minute sac-like structures called alveoli. It is here that blood is brought into close contact with the oxygen molecules and under the influence of pressure the oxygen diffuses, or passes through, the capil lary membrane and into the blood. Here, it attaches itself to a protein molecule, within the red blood cells, called haemoglobin for its transportation around the body. The oxygen will remain attached to the haemoglobin until it enters an area where the oxygen content is low, whereupon the haemoglobin releases the oxygen, allowing it to diffuse into the tissues. Carbon dioxide is dissolved in the blood which carries it to the lungs with any unused oxygen for expiration. See Figure 3-2.



Trachea Air

t !

Lungs

Bronchus

Bronchiole

Air

THE LUNGS Page 3-2

Alveoli covered with minute blood-tilled capillaries

Figure 3_2: Lung, Bronchial Tree and Alveoli

Breathing is an automatic process directed by the brain. As the need to increase oxygen intake, or carbon dioxide elimination fluctuates, so the brain controls the rate and depth of breathing.

Oxygen rich blood takes on a bright red colour, whilst oxygen deficient blood has a bluish colour.

D- THE EFFECTS OF REDUCED PRESSURE

As mentioned earlier, the oxygenation of blood in the lungs is dependent on pressure. To be precise, a pressure gradient, ie greater pressure on the outside forces oxygen into an area of lower partial pressure in the blood. It becomes obvious now why the understanding of this process is important to pilots. As we gain altitude we know that pressure decreases, therefore the driving pressure for oxygen absorption will also decrease resulting in a reduced flow of oxygen into the blood. There is some compensation as a result of the strong attraction between haemoglobin and oxygen, but this reaches a critical point above 1 0 000 ft. In more scientific terms, to emphasise this fact, at sea level the partial pressure of oxygen in the alveoli is 1 03 mm Mercury (Hg), but at 1 0 000 ft it is 55 m m Hg!

The reduction in the amount of oxygen can and does lead to a decrease in human performance.



ALTITUDE ATMOSPHERES

1 Occ 50,000 <0.1

40,000

30,000

20,000

1 0,000

5,000

1 cc Sea Level 1

0.5cc -30 2

0.33cc -60 3

THE LUNGS Page 3-3

PARTIAL PRESSURE

OF AIR - OF OXYGEN - OF OXYGEN

IN ALVEOLI (P Air) mm Hg

82

1 41

226

349

523

632

760

(PO,) mm Hg

1 7

30

47

73

1 1 0

1 30

1 60

(PO,Aiv) mm Hg

1 8

55

76

1 03

Figure 3.3 : Altitude-pressure relationship

Volume:

A 1 cc bubble of air at sea-level will increase to 1 Occ at 50,000 ft and decrease to 0.33cc at 60 ft below sea-level. (NB Scuba divers) .

Pressure:

Atmospheric and partial pressure decrease with increasing altitude and increase below sea-level.

NOTE: See also Barotrauma, page 6-1 .

E. HYPOXIA

1 . DEFINITIONS

HYPOXIA is the condition under which the oxygen concentration at the tissue level is less than normal.

ANOXIA is the condition where there is a total absence of oxygen.



2. CAUSE AND SYMPTOMS

THE LUNGS Page 3-4

There are many causes of hypoxia, but in the aviation context the greatest risk occurs as a result of an increase in altitude, with its attendant drop in partial pressure. The first symptoms of hypoxia are usually associated with mental functions owing to the fact that brain tissues are the most sensitive to a lack of oxygen. Obviously, the rate at which the observed effects occur will depend upon the altitude. Earlier, the figure of 1 0 000 ft was mentioned, but it is possible even at 8000 ft to observe signs of mental impairment, although generally healthy persons should not be noticeably affected up to 1 0 000 ft. From 1 0 000 ft upwards, however, the effects become more noticeable and the symptoms, similar to the effects of alcohol, can be summarised as follows:

JUDGEMENT

Reduced performance as a result of the loss of self-criticism.

CHANGE IN PERSONALITY

Behaviour changes as a result of euphoria, aggression or loss of inhibitions.

MUSCULAR CONTROL

Mental impairment results in poor muscular control and uncoordinated movements.

REDUCED MEMORY/CONCENTRATION

The loss of short term memory can result in difficulty in carrying out normal operating procedures.

EFFECT ON SENSES

Peripheral vision and night vision are first affected, followed by day vision, colour vision, touch and hearing.

REDUCED CONSCIOUSNESS

If hypoxia continues, the level of consciousness reduces, resulting initially in light-headedness, dizziness and confusion, then semi-consciousness, unconsciousness and ultimately death.

3. FACTORS AFFECTING SUSCEPTIBILITY TO HYPOXIA

The effects of hypoxia may vary from individual to individual and although no one can resist its effects, susceptibility to hypoxia can be increased by various factors, including:

FATIGUE/STRESS

Tiredness, perhaps from extended flight duty, can increase the onset of hypoxia.

ALTITUDE

The greater the altitude, the greater the effects.

COLD

More energy must be generated to counteract cold, resulting in an increased demand for oxygen, while circulation is slowed and consequently increases the advance of hypoxia.

EXPOSURE TIME/RATE OF ASCENT

The longer the exposure to hypoxia and the faster the rate of ascent, the greater the effect will be.

ILLNESS/HEAT

Even mild illness or heat exposure makes demands on the energy supply of the body and therefore the oxygen requirement, increasing the onset of hypoxia.

EXERCISE

As with cold and illness, this makes demands on the body's energy supply and therefore oxygen, increasing the degree of hypoxia.



ALCOHOL, DRUGS AND TOBACCO

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The intake of alcohol has similar effects to those of hypoxia, including a reduced tolerance of altitude. Many drugs depress brain function and slow the rate of breathing which can further aggravate hypoxia. Smoking creates carbon monoxide as a by-product for which haemoglobin has a greater affinity than it has for oxygen, with the result that there is less haemoglobin available to transport oxygen through the system, thus enhancing the effects of hypoxia.

PHYSICALLY

The skin becomes pale and a bluish tint may become noticeable, particularly the finger tips, lips ears and nose, (this is called Cyanosis), as well as air hunger accompanied by yawning.

G FORCE EXPOSURE

This affects efficient oxygen uptake from the lungs.

Some of the factors mentioned above are unavoidable to the pilot, whilst others are self-induced by personal habits. However, the importance of understanding and recognising the signs and symptoms of hypoxia and the corrective action to be taken, cannot be over emphasised.

For those interested in facts and figures, the following may be interesting, if not enlightening! Having acquired an understanding of the physiology, effects and symptoms of hypoxia, the question arises as to what to do about it. In particular, the time taken to do something about it. In this regard the term TIME OF USEFUL CONSCIOUSNESS is significant.

The time of useful consciousness is generally regarded as being the maximum length of time, after an individual has been deprived of his oxygen supply, during which he is able to carry out some useful or meaningful task, without supplemental oxygen, and before he or she loses consciousness. It is also considered to be the time available to recognise the onset of hypoxia and do something about it. This time is variable, not only according to altitude, but from individual to individual. It will also be shortened by physical activity and other factors. The following figures are fairly representative of the various times for a normal healthy person.

22 000 ft 4 - 8 minutes 25 000 ft 2 - 3 minutes 30 000 ft 30 seconds to one minute 35 000 ft 1 5 - 30 seconds 40 000 ft 1 0 - 20 seconds.

4. HYPOXIA CLASSIFICATION

HYPOXIC HYPOXIA

This is a condition where there is insufficient oxygenation of the blood in the lungs. This can be as a result of a decreased partial pressure of oxygen (PO,) in the Alveoli, thus the blood returning to the heart from the lungs contains less oxygen and therefore the tissues get less. In aviation this situation develops with a height above 8000 ft. It can also be caused by lung disease and even smoking!

ANAEMIC HYPOXIA

This condition is found in cases of blood loss from severe bleeding or donation, or decreased amounts of haemoglobin from menstruation, chronic infection or an iron deficiency, possibly owing to diet, with the result that there is a decrease in the total circulating haemoglobin. It can also occur in cases where there is an abnormally high carbon monoxide presence in the blood, reducing haemoglobin availability. It should be noted that the South African Civil Aviation Regulations, 1 997, (Part 91) require a period of 72 hours following blood donation before a flight crew member may fly.

STAGNANT HYPOXIA

This condition can occur where there are heart or circulatory problems. The blood generally has normal haemoglobin and oxygen levels, but poor circulation results in less oxygen than is required reaching the tissues. This can be found in cases of shock, where there is a drop in the total effective circulating blood volume (the muscular walls of the arteries relax, which effectively widens them) as well as certain anatomical and functional disturbances of the blood circulation.

HYSTOTOXIC HYPOXIA

This can occur as a result of the poisoning of cells or tissues, rendering them unable to utilise the oxygen supplied in the blood. This can also occur when a person is under the influence of alcohol or drugs.



5. METHODS TO COMBAT HYPOXIA

Clearly, the problems involved with combating hypoxia are two-fold:

(a) Providing an adequate supply of oxygen.

(b) Maintaining an adequate pressure gradient.

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Depending on the individual, the body is able to compensate to a degree by increasing the heart rate and breathing rate. Good physical condition, an age over 25 years and pilots who fly regularly exposed to mild hypoxia, have a higher tolerance to the effects of hypoxia.

In modern aircraft which rely on high altitude operation for good performance, this is provided by cabin pressurisation. An aircraft flying at 30 ooo ft may, by pressurisation, provide an environment equivalent to approximately 6000 ft.

In aircraft without pressurisation, breathing a gas mixture (oxygen and nitrogen) via face rnasks, is necessary. As altitude is gained, an increasing percentage of oxygen is added until the point is reached where 1 00% oxygen is being breathed. This usually occurs at approximately 40 000 ft. Above this height, because of the pressure gradient requirement, oxygen would have to be delivered under pressure, a technique known as Positive Pressure Breathing (PPB).

F. HYPERVENTILATION

1 . DEFINITION

Hyperventilation effectively means over breathing, or breathing at a rate in excess of that required for normal physiological purposes. Its cause is not restricted to hypoxia, but can be the result of motion sickness, anxiety, heat, vibration or pain.

2. CAUSE

The rate and depth of breathing is usually controlled to maintain constant levels of carbon dioxide in the body. It should be remembered that in terms of the treatment for hypoxia, no reference was made to increasing the breathing rate as an answer to reduced oxygen pressure in the lungs. The "breathing drive" is a function of increased carbon dioxide and not decreased body oxygen. An unnecessarily high breathing rate will remove carbon dioxide at an abnormally high rate resulting in changes in the circulation, most significantly in the brain. This change in circulation causes a reduction in the diameter of the arteries to the brain, which then receives a reduced supply of oxygen. An everyday example of this is to blow up a balloon rapidly, you will soon feel light-headed.

Primary hyperventilation caused by emotional responses occurs most commonly amongst anxious, inexperienced young pilots during stressful situations. Other causes include pain, vibration and motion sickness. If a pilot suspects hypoxia and intentionally starts to hyperventilate in the mistaken belief that this will solve the problem, it can start a vicious cycle which can physiologically very rapidly lead to loss of consciousness.

3. SYMPTOMS

The symptoms are very similar to those of hypoxia and, therefore, hyperventilation is often confused with hypoxia. The classic symptoms of hyperventilation are:

(a) Light-headedness or dizziness.

(b) A tingling, or numbness of the fingers, hands, toes and lips.

(c) A stiffening of the fingers, hands, toes and lips.

(d) Anxiety and chest pains

(e) Reduced performance

(f) Tunnelling or clouding of vision (g) Stiffening/spasm of peripheral limb muscles.

(h) Collapse and unconsciousness, during which breathing returns to normal and the subject will recover.



4. TREATMENT OF HYPERVENTILATION

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Because the symptoms of hypoxia and hyperventilation are similar, it is important for treatment purposes not to make the mistake of assuming the one and not the other. Both conditions may be present at the same time. A simple rule is to assume the worst. In other words if the pilot is at an altitude at which it is possible for hypoxia to occur, he should take steps to use oxygen, if available, or reduce altitude. If, however, the altitude is less than 1 0 000 feet, the symptoms should be regarded as those of hyperventilation and the following steps should be taken:

(a) Reduce breathing, both in rate and depth. (b) The ideal is to breath into a paper bag. This re-breathing of expired air, a mixture of carbon

dioxide and oxygen, will usually cut short the attack.

NOTE: It may be difficult, but the subject should be encouraged not to increase the rate and depth of breathing, as this will only exacerbate the situation.

G. LOSS OF CABIN PRESSURE

The procedures to be followed in the event of cabin decompression, will be extensively covered during the technical and practical aspects of conversion to aircraft type. However, in the context of hypoxia it is important to consider the following:

Effectively there are two situations involved.

1 . A gradual loss of pressure, in which case the pilot or crew would take the necessary steps to reduce altitude to avoid exposing passengers to hypoxia. Use of oxygen masks may have to be considered in mountainous terrain.

2. A sudden and rapid loss of cabin pressure, with a resultant abrupt exposure to hypoxia, cold and even decompression sickness (see Chapter 6, Pressure). The aircraft would have to descend rapidly to a lower altitude and passengers and crew would need to use oxygen masks immediately.

The danger of rapid decompression is that the aircraft acts like a venturi, the aerodynamic effect of which would be to suck air out of the aircraft creating a cabin altitude, owing to the reduced pressure, higher than the actual altitude. The need for rapid crew response in both controlling the aircraft and ensuring emergency oxygen for passengers, goes without saying.

H. DISORDERS, DISEASE AND ILLNESS

1 . HYPOXIA and HYPERVENTILATION

Both of these have already been covered in detail, constitute the most obvious problems for pilots, and can be considered temporary conditions.

2. ASTHMA

This is a medical condition resulting in the narrowing of the airways of the lungs due to inflammation and muscular contraction. The cause is generally unknown, but possible contributing factors include stress, allergy and temperature. The condition results in inadequate ventilation of the lungs; breathing in (inspiration) is relatively normal but breathing out (expiration) is restricted with exhaustion and hypoxia resulting. Relief may be achieved through the use of broncho dilators. It can affect anyone at any time.

3. BRONCHITIS

This is an inflammation/infection of the mucous membrane that line the airways and is usually a complication of other diseases such as the common cold or influenza. Symptoms are a phlegm producing cough and mild fever. It is treated with anti-biotics and lasts about ten days.

4. PLEURISY

This is a localised area of infective inflammation on the outer surface of the lung which causes a sharp chest pain aggravated by deep breathing. It is treated by antibiotics and anti inflammatories.

The more serious and lasting illnesses associated with the lungs would in all probabil ity preclude the pilot from flying again.



QUESTIONS

(ANSWERS ON PAGE 1 1 -1)

1 . As altitude is increased above sea level:

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(a) the partial pressure exerted by oxygen in the atmosphere remains constant, while its percentage composition of the atmosphere decreases,

(b) the partial pressure of oxygen in the atmosphere decreases, while that of carbon dioxide increases,

(c) the partial pressure of oxygen, as well as all the other gases in the atmosphere, decreases, (d) both the partial pressure exerted by oxygen in the atmosphere and its percentage composition of

the atmosphere decrease.

2. Hypoxia is:

(a) a regular occurrence in pressurised aircraft at an altitude of more than 1 0 000 ft above sea level, (b) a measure of the blood's oxygen saturation, (c) directly related to the rate of ascent and not the final cruise altitude, (d) the immediate result when a person breathes at a rate in excess of that normally required.

3. The first symptoms of hypoxia usually start occurring at altitudes above 1 0 000 ft and:

(a) are very easily and immediately detected pilots, (b) are usually associated with decreased mental functions, (c) loss of muscular control is one of the earliest manifestations, (d) can be resisted by reducing the rate of breathing.

4. Susceptibil ity to hypoxia:

(a) can be reduced by breathing very slowly, (b) increases rapidly in persons over the age of 25 years, (c) increases in pilots who fly regularly exposed to mild hypoxia, (d) increases with the use of alcohol, drugs and tobacco,

5. Resistance to hypoxia can be increased by:

(a) drugs which slow down the circulation and therefore the rate of oxygen consumption, (b) the valsalva manoeuvre which forces more oxygen into the blood, (c) being in a good physical condition and 25 years of age and over, (d) reducing the breathing rate.

6. Hypoxic hypoxia is defined as:

(a) a condition where there is insufficient oxygenation of the blood in the lungs owing to decreased partial pressure of oxygen in the alveoli,

(b) a condition where, owing to blood loss, there is a decrease in the total circulating haemoglobin, (c) a condition where there are heart or circulatory problems, (d) a condition when a person breathes at a rate in excess of that normally required.

7. The time of useful consciousness at 30 000 ft is approximately:

(a) 30 - 60 seconds, (b) 1 o - 20 seconds, (c) 2 - 3 minutes, (d) 1 5 - 30 seconds.

8. Hyperventilation, or overbreathing, occurs most commonly:

(a) as a result of increased body carbon dioxide, (b) when there is a decrease in the total circulating haemoglobin, (c) in pilots over the age of 25 years who fly regularly exposed to mild hypoxia, (d) in conditions of anxiety.



9. Symptoms of hyperventilation include:

(a) loss of all muscle tone,

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(b) a light-headedness with a tingling or numbness of the fingers, hands, toes and lips, (c) a pale skin with a bluish tint of the finger tips, lips, ears and nose, (d) decreased mental functions.

1 0. The expression "time of useful consciousness" refers to the time taken at a specified altitude:

(a) to carry out a specific task, (b) to deal with an emergency situation such as an engine failure, (c) to recognise the onset of hypoxia and do something about it, (d) to operate without oxygen before becoming unconscious.

1 1 . The immediate treatment for hyperventilation should be to:

(a) increase the rate and depth of breathing, (b) breathe pure oxygen through a mask, (c) reduce the rate and depth of breathing, (d) assume a position which will encourage blood to flow to the head.

1 2. Methods of combating hypoxia include:

(a) breathing into a paper bag, (b) increasing the rate and depth of breathing, (c) maintaining an adequate oxygen pressure gradient, (d) decrease the rate and depth of breathing.

1 3. Anaemic hypoxia can occur as a result of:

(a) emotional stress, (b) an excessive rate and depth of breathing, (c) a low body temperature, (d) blood loss from severe bleeding.

14. Cyanosis is likely to result from:

(a) hyperventilation, (b) high levels of carbon dioxide in the blood, (c) hypoxia, (d) high blood pressure.

15. Blood which is bright red in colour:

(a) is rich in oxygen, (b) is deficient in oxygen, (c) has a high glucose content, (d) has a high level of carbon dioxide.

1 6. As altitude increases:

(a) the partial pressure of oxygen increases, (b) the time of useful consciousness increases, (c) the possibil ity of hyperventilation decreases, (d) the time of useful consciousness decreases.

17. The breathing drive is a function of:

(a) a decrease in the amount of oxygen in the body, (b) the level of carbon dioxide in the body, (c) the body's temperature, (d) the pulse rate.



CHAPTER 4

A. INTRODUCTION

THE EARS

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The ear has two very important, but different, functions: hearing and balance. These senses function independently of each other, and whilst it is obviously important for a pilot to be able to hear, it would not be incorrect to say that after vision, balance is the second most important sense. It follows, then, that a good understanding of this function is of considerable value for pilots.

B. PHYSIOLOGY OF THE EAR

The ear comprises three clearly defined parts: the outer ear, middle ear and inner ear.

auditory canal

1 . THE OUTER EAR

Ossicles

Ear drum

Cochlea

Semi-circular

Eustachian tube

Figure 4-1: Anatomy of the ear

Auiditory nerve

The outer ear is simply a sound gathering device. It comprises a flap of cartilage, more correctly known as the pinna or auricle, the purpose of which is to collect sound waves which are then passed through an irregularly shaped canal, called the external auditory canal, to the eardrum or tympanic membrane which forms the divider between the outer and middle ear. The canal, or passageway, contains hairs and wax producing glands, the purpose of which is to trap external matter thus preventing it from reaching, and possibly infecting, the hearing mechanism. A build up of wax in this passageway can, of course, result in some hearing loss since it will prevent sound waves from reaching the ear drum.

2. THE MIDDLE EAR

The middle ear is a very small air filled chamber which contains the amplifying equipment; three linked bones, collectively known as ossic/es. These bones are vital to the mechanical transmission of sound waves and are individually named according to their shape: the malleus, or hammer; the



THE EARS Page 4-2

incus, or anvil; and the stapes, or stirrup which also happens to be the smallest bone in the human body.

Malleus (Hammer)

Figure 4-2: The Ossic/es

Incus (Anvil)

The process of hearing commences when the sound waves strike the eardrum, causing it to vibrate. This vibration is picked up by the malleus, which is situated next to the eardrum and is passed by a lever action to the adjoining incus, which in turn transmits the vibration to the stapes. This tiny bone lies in an opening, called the oval window, located on the inner wall of the middle ear from where the vibration passes to the inner ear. During this process amplification of the original sound wave takes place, so that by the time it reaches the inner ear the vibrations have become far more concentrated. The air pressure in the middle ear chamber is kept the same as atmospheric pressure by a vent or tube called the Eustachian tube which links the interior of the middle ear with the nasal passages.

Since it is not possible, or should not be, for air to pass through the eardrum, the only means of venting pressure is through the Eustachian tube, a function which becomes necessary when climbing or descending. This process can be hindered by a cold or other similar infection where the resultant swelling or inflammation can block the Eustachian tube rendering it impossible or very difficult to equalise the pressure. This problem is more pronounced during descending flight, especially at high rates of descent, when the increasing external pressure pushes the eardrum inwards. Normally this will be partially balanced by the Eustachian tube, except that the flow of air into the tubes does not occur as easily as the flow out of them. Clearly the problem is exacerbated by a reduction in the diameter of the tube as a result of infection. It becomes obvious, then, that pilots should avoid flying if they are experiencing any form of upper respiratory tract infection, for example the common cold. Apart from the severe pain which will be experienced, the middle ear may also be damaged resulting in some hearing loss, which may become permanent. In very extreme cases, even the balance mechanisms of the ear may be affected, a condition which is called pressure vertigo. See a/so Chapter 6, Pressure, page 6-2.

3. THE INNER EAR

The inner ear comprises two particularly important pieces of equipment: the cochlea for hearing and the vestibular apparatus for balance. The importance of this dual role possibly explains why it is one of the most protected parts of the body. Cushioned by fluid, it is located within the rigid skull.

It is within the cochlea that sound waves are finally converted into nerve impulses which are then transmitted via the auditory nerve to the brain for interpretation as sound. The cochlea, a small bony structure, contains as many as 20 000 minute hair-like cells arranged along a membrane that coils around itself resembling a snail shell. The sound waves transmitted by the stapes to the oval window create pressure waves in the fluid of the cochlea causing the sensory cells to vibrate and generate nerve impulses which are transmitted to the brain. Excessive noise, particularly over long periods, can damage the very fragile hair-like cells, causing permanent hearing loss.

C. HEARING LOSS

Hearing loss can be divided into two areas:

1 . CONDUCTIVE LOSS

The conductive system concerns the outer and middle ear, the components of which are the ear drum and the ossicles. Hearing loss in these areas may be summarised as follows:

(a) Congenital abnormalities, eg deformation of the ear canal; (b) Wax, which can build up and completely block the canal; (c) Infections in the canal can cause swelling, which may partially or completely block the canal;



(d) Bony outgrowths from the skull can protrude into and obstruct the ear canal; (e) Infection of the middle ear, perhaps from a throat or nose cold.

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(f) Perforation of the ear drum may occur as a result of very loud sounds or chronic infections of the middle ear. The actual hearing loss is determined by the size and position of the perforation;

(g) Allergies can cause swelling and inflammation of the ear drum; (h) Disorders, ie thickening and fusion, of the bony organs of the middle ear will cause poor trans-

mission of sound. This can occur through an inherited disorder and with age.

In many cases, conductive loss is reversible. Colds and flu pass; allergies can be controlled; surgery can repair a perforated eardrum, remove growths etc. The important aspect for pilots is to be aware of the problem, to treat it and not aggravate it until the problem becomes permanent.

2. NON-CONDUCTIVE LOSS

This type of hearing loss is usually associated with inner ear pathology and is mostly non-reversible. It can be summarised as follows:

(a) Malformation due to infection, use of harmful drugs or vitamin deficiency, especially during pregnancy;

(b) Jaundice or anoxia just after birth; (c) Untreated middle ear infection; (d) Presbycusis, a natural loss of hearing with age. After the mid twenties there is a gradual

hearing loss, affecting firstly the higher frequencies and only later the lower frequencies. This can be further aggravated by tobacco, alcohol, copper, chronic infections and vascular problems.

NOISE INDUCED HEARING LOSS

Exposure to noise of sufficiently high intensity may result in temporary or permanent loss of hearing. The hearing loss may occur in two different ways:

(a) FROM A CONSTANT, OR LONG TERM EXPOSURE TO A HAZARDOUS NOISE ENVIRONMENT.

The extent of the damage in this case may be temporary, but prolonged exposure may result in permanent loss. Initially, temporary hearing loss may be accompanied by a high pitched ringing sound, (referred to as tinnitus), a feeling of fullness within the ear and muffled hearing. Recovery may occur within a few hours or a few days.

(b) A SUDDEN, EXPLOSIVE NOISE.

In this case permanent damage may result, with possibly a ruptured ear drum, damage to the delicate ossicles and ultimately irreversible damage to the very sensitive membrane in the cochlea.

D. SOUND

Sound waves are made up of two distinct parts:

1 . The loudness or intensity of the sound, which is measured in decibels; 2. The pitch, or frequency, which is measured in Hertz (Hz).

It is the decibel level which, in terms of hearing loss, is the more significant. Examples of decibel levels include:

(a) Whisper -20dB; (b) Normal conversation - 50-?0dB; (c) Typical noise level in the cockpit of a light aircraft - 95dB.

As the decibel level increases, the discomfort of loud noise gives way to severe pain.

Constant exposure to noise levels above 85 dB may cause temporary or permanent hearing loss. As indicated above, the noise level in a light aircraft can be as high as 95 dB. Pilots should, therefore be aware of the noise environment in which they operate and use suitable hearing protection.



E. VESTIBULAR SYSTEM

THE EARS Page 4-4

The second function of the inner ear is balance. This is achieved by the vestibular system, comprising the Semi-circular Canals and the Otolith Organs, which are able to detect angular and linear accelera· tions, but not velocity.

Posterior Semi-circular canal (Pitch)

Lateral Semi-circular canal (Yaw)

1 . SEMI-CIRCULAR CANALS

Anterior Semi-circular

4------ canal (Roll)

Vestibule, containing the Utricle and Saccule

Figure 4·3 : Vestibular apparatus

These comprise three semi-circular tubes, filled with a fluid called endolymph, which are located at right angles to each other and are capable of sensing accelerations as low as 0.05°/second'. An enlarged portion of each canal, called the ampula, contains a gelatinous mass, called a cupula, containing minute hairs projecting from hair cells at the base of each ampula. These cells are connected to sensory nerve fibres which in turn pass into the vestibular nerve. Movement of the fluid bends the cupula which stimulates its nerve cells, and the resultant electrical signals which are transmitted to the brain are interpreted as angular, or rotary, accelerations. The orientation of the semi-circular canals is almost exactly the same as the three planes of movement of an aircraft and they are thus able to detect accelerations in pitch, roll and yaw. See Figure 4-4.

Sensory hairs

�Nerve

Canal filled with endolymph

Am pula

Figure 4·4: Cross section of a Semicircular Canal

For purposes of explanation regarding angular accelerations, let us assume that the aircraft rolls into a turn to the right, an action which will be detected by the anterior semi-circular canal. The canal rolls to the right, causing the fluid to lag behind effectively moving it in the opposite direction and causing the cupula to move in the direction of the roll signalling the angular acceleration to the brain. Once the acceleration has stopped, with the aircraft remaining in a steady turn for some 10-1 5 seconds, the fluid stops moving, the cupula returns to the normal position and the sensation of roll stops even though the turn continues. See Figure 4-5.



(a) Level tliQht (b) Roll to riQht

Figure 4-5: Angular Acceleration

2. OTOLITH ORGANS

(c) Steadv turn

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These organs, comprising the utricle and the saccule, are stimulated by linear accelerations, greater than 0.1 m/second2, in the horizontal and vertical planes. They are located within the vestibule at the base of the semi-circular canals, on either side of the head. With the head in an upright position, the utricle lies in the horizontal plane and the saccule in the vertical plane. Each organ contains a macula, similar to the cupula, comprising a gelatinous layer within which small calcified particles called otoliths lie on top of groups of sensory hairs extending from hair cells which are attached to the vestibular nerve.

When the head leans forward, otolith pressure causes the hairs to bend forward and when the head leans backward they cause the hairs to bend backward. Similarly if the head moves to one side the hairs will be forced to bend towards that side. The hair cells are oriented in different directions so that the varying positions of the head stimulate different hair cells and in so doing alert the brain, via the nervous system, of the position of the head relative to the force of gravity. For normal, ground-based, everyday operations such as running, walking or turning the head, the system is adequate. From the pilot's perspective, however, the otolith organs cannot distinguish between the force of gravity and other linear accelerations which affect the pilot in the air. The otoliths possess greater inertia than the fluid which surrounds them, so if the body is moved suddenly forward the otoliths effectively remain behind, moving backwards over the hairs. The brain receives two sensory inputs: one telling it that the body is accelerating forward and the other that gravity is continuing to work in the normal direction. These two vectors are resolved by the brain into a perceived sensation of the body tilting backwards, or an assumption that the aeroplane has pitched up. The reverse happens in the case of a sudden deceleration. See 1 (b) on the next page.



Force of gravity X

(a) Straight and Level

X

(b) Acceleration

Figure 4-6: Linear Acceleration

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Reaction due to acceleration

Resultant of both vectors which brain perceives as gravity

Again, it is important to remember that the vestibular system is only able to detect the initial acceleration, once this has stopped either at a steady or even zero speed the system returns to normal.

The vestibular system alone is not responsible for balance; information from the system is used together with cues from the visual and postural systems to maintain spatial orientation. Nausea can result from massive stimulation of the system; particularly three dimensional stimulation.

F. S PATIAL DISORIENTATION

This condition refers to one in which the subject is unable to perceive his position, attitude and motion relative to the earth. The condition can be attributed both to vestibular and non-vestibular causes.

1 . VESTIBULAR

The vestibular system is more than adequate for normal ground operations such as running, walking or turning the head. For flying, however, it is inadequate. The response time of the semi-circular canals to angular accelerations encountered in flight, is too slow. Also, the otolith organs are not able to distinguish between the force of gravity and other linear accelerations which act upon the pilot. Errors, therefore, occur in the vestibular system leading to spatial disorientation. In flight it is possible for the semi-circular canals to allow some angular accelerations, those below the threshold of detection, to remain unperceived, yet cause the perception of others which actually do not exist.

(a) THE LEANS

The classic example of this occurs during the early stages of instrument flying training. If the pilot inadvertently rolls into a turn at a rate below the detection threshold of the semi-circular canals, he may perceive his wings to be level. If the pilot now realises this situation from instrument indications and rolls out of the turn at a rate which does stimulate the semi-circular canals, he may indeed roll the wings level but feel as though he has banked away from the wings level situation, will feel compelled to align his body with the perceived vertical and will actually lean in the direction of the original sub-threshold roll. This illusion is known as "the leans".

(b) OCULOGRAVIC/SOMATOGRAVIC ILLUSION

The second type of vestibular illusion is that caused by linear acceleration. In I evel flight at a constant speed, the only force experienced by a pilot is that of his own weight downward. During an acceleration, an inertial force is produced in the longitudinal axis of the aircraft, backwards. The resultant vector, downwards and backwards, causes the otoliths to interpret



THE EARS Page 4-7

this acceleration as a pitch up. Deceleration causes a pitch down illusion. This illusion is commonly experienced shortly after take-off at night over unlighted terrain or water. See Figure 4-6.

(c) CORIOLIS EFFECT

The arrangement of the semi-circular canals is such that each one lies in a different axis of motion, ie one each in the axes of pitch yaw and roll. Angular acceleration in any of these axes will cause the endolymph to move thus stimulating the vestibular apparatus and creating the awareness of movement in that particular axis. As soon as a constant flow of endolymph has been achieved, the stimulus from the canal ceases although the endolymph continues to flow. If the head is moved during this motion, for example if the pilot were to look up, the original sensing canal will be moved out of the axis of motion to be replaced by another canal moving into the new axis of motion. The endolymph flow in the original canal will slow down thus creating a sensation of motion in the opposite direction to that of the aircraft. Endolymph flow will occur in the newly aligned canal thus creating the sensation of motion in its particular axis. The effect of this combined stimulation is to cause a tumbling sensation.

(d) GRAVEYARD SPIN

Whilst the semi-circular canals are able to determine angular accelerations, they are unable to perceive angular velocity. The resultant effect presents itself during a spin, with no external reference. When the pilot enters the spin, he undergoes an initial angular acceleration and continues to perceive the angular motion of the spin after the angular acceleration has ceased. This may last for up to 20 seconds, during which time the endolymph velocity relative to the canal reaches zero, resulting in the perception that motion has ceased. If the pilot now initiates a recovery from the spin, he will undergo a deceleration interpreted by the semi-circular canals as a spin in the opposite direction. Reluctance to believe and obey the aircraft's instruments and deprived of external reference, the pilot is tempted to make a correction in the opposite direction to the perceived spin thereby placing the aircraft further into the original spin. This is known as the graveyard spin, for obvious reasons.

(e) GRAVEYARD SPIRAL

The graveyard spiral is similar in effect to the graveyard spin, except that it follows a co-ordinated turn at constant rate. Again, the endolymph velocity relative to the canal reaches zero, no motion is perceived and the pilot loses the sensation of turning. The inexperienced pilot, with no visual cues, will allow the aircraft to lose height and in an attempt to correct this may be tempted to apply elevator and even power, with the result that the turn becomes tighter and the aircraft will enter a spiral dive. Once this happens, the pilot will perceive a turn in the opposite direction and if he does not follow his instruments, but trusts his sensation, will tend to tighten the turn still further in an attempt to roll out of the turn, with the logical conclusion.

(f) INVERSION ILLUSION

If an abrupt change from a climb to straight and level is made, this may create the illusion of tumbling backwards. A pilot so disorientated may react by pushing the aircraft into a nose low attitude with a resultant increase in the illusion.

(g) ELEVATOR ILLUSION

When an aircraft is subjected to an abrupt upward vertical acceleration, perhaps by an updraft, the illusion of being in a climb can be created. In response, the disorientated pilot will react by pushing the aircraft into a nose low attitude. Similarly, an abrupt downward vertical acceleration will create the illusion of being in a descent, with the pilot reacting by pulling the aircraft into a nose up attitude.

2. MOTION SICKNESS

The combination of vestibular and visual signals supplied to the brain enable it to establish spatial orientation. In a situation where the inputs of these signals to not concur, disorientation occurs which may lead to motion sickness, the symptoms of which include nausea and sweating. The primary cause of motion sickness can best be described as an over-stimulation of the vestibular or balance system of the ear, most probably due to the repeated vertical motion of the aircraft in turbulent air. Some psychological factors, such as nervousness or stress, may also influence the onset of motion sickness. For the majority of people it is a temporary condition which will ultimately disappear once the aviation environment becomes more familiar. Methods which may be used to reduce the effect on passengers are:



* Try and avoid areas of expected turbulence. * Increase the supply of fresh air. * Avoid sudden or rapid control movements. * Closing the eyes will remove one of the mis-matched signals to the brain. * Fixing the eyes on the natural horizon.

THE EARS Page 4-8

Flight crew who suffer from this condition should avoid taking motion sickness drugs because in most cases they produce side effects which tend to affect performance.

3. VERTIGO

This can best be described as a sensation of rotation when in fact no such rotation is occurring, or a sense of dizziness as a result of the vestibular system being unable to adapt to an abrupt or unexpected motion. Its cause can also be ascribed to infection of the upper respiratory tract, fatigue, discomfort, self-medication and pressure changes within the inner ear. It can occur under conditions of high g-loading in steep turns or spiral dive recoveries where there is an absence of a visual horizon reference and the pilot is not trained, or not current, in the use of the aircraft instruments.

Pressure Vertigo, or alternobaric vertigo, can occur as a result of the inability of the eustachian tube to equalise pressure between the ear and the outside, especially where the pressure change affecting both ears is unequal.

Flicker Vertigo can be caused by a flashing light, such as an aircraft strobe light being reflected from cloud or fog, or the sun a or a bright light shining on a rotating propeller blade or through helicopter rotors.

CONCLUSION

By now it will have become apparent that the human body was not designed for flight; the structure and components are specific for a ground-based life style. From birth, gravity, the natural horizon, the eyes and inner ears have been the primary references for our spatial orientation. Spatial disorientation occurs when these previously reliable organs of orientation are affected by the varying accelerative forces of flight, and illusions and false sensations result when our natural cues have either been removed or changed.

The danger for the pilot is to base the control of an aircraft on these false perceptions.

Most pilots are affected by disorientation at some time and are usually able to resolve the problem as soon as natural cues are obtained, for example the natural horizon. It is when we are totally isolated from these natural cues, perhaps when flying in cloud, that we face the greatest risk. It becomes obvious why so much instrument flying time is required for the issue of an instrument rating. Apart from being taught to control the aircraft by reference to these instruments, it is the belief in these instruments that is equally as important. In forty hours of instrument training we are trying to overcome a lifetime of trusting what we see and feel.

Private Pilot Licence Revision: 12/201 o


QUESTIONS


1 . Non-conductive hearing loss is usually associated with the inner ear and:

(a) middle ear infections are a common cause, (b) age plays no roll in non-conductive hearing loss, (c) allergies are a common cause of non-conductive hearing loss, (d) is easily reversible through medication.

2. A person who is suffering from vertigo will:

(a) experience constant ringing in the ears, (b) be unable to equalise the the pressure in the middle ear, (c) have a temporary loss of hearing, (d) be subjected to a false sense of rotation.

3. The vestibular system comprises:

(a) the semi-circular canals only, (b) the semi-circular canals, the otolith organs and the eyes, (c) the semi-circular canals and the otolith organs, (d) the otolith organs only.

THE EARS • QUESTIONS Page 4-01

4. Because a pilot's environment is one of constantly changing pressure, he or she:

(a) should not fly with a head cold, throat, ear or sinus infection, (b) should not allow their teeth to be x-rayed, as this can cause the formation of small pockets of air

in the fillings, (c) should not take part in any form of scuba diving.

5. The Eustachian tube is used to:

(a) conduct sound waves from the outer to the inner ear, (b) equalise pressure on both sides of the ear drum, (c) prevent "decompression sickness" in divers who have to fly soon after a dive exceeding 30 ft, (d) sense linear accelerations.

6. The function of the Eustachian tube is to:

(a) equalise pressure in the middle ear, (b) equalise pressure in the inner ear, (c) prevent changes in pressure in the middle ear, (d) sense angular accelerations.

7. The primary function of the semi-circular canals is to:

(a) sense linear accelerations, (b) sense angular accelerations, (c) sense gravitational accelerations, (d) equalise pressure between the middle and outer ear.

8. The function of the ossicles in the human ear is to:

(a) sense angular accelerations, (b) equalise the pressure between the middle ear and the outer ear, (c) convert sound waves into nerve impulses before they are transmitted to the brain, (d) pass sound waves from the ear drum to the inner ear.



9. The function of the cochlea in the human ear is:

(a) to pass sound waves from the ear drum to the inner ear, (b) to sense linear accelerations,

THE EARS - QUESTIONS Page 4-02

(c) to convert sound waves into nerve impulses before they are transmitted to the brain, (d) balance.

1 o. Spatial orientation is maintained:

(a) only by the vestibular system, (b) only through visual cues, (c) only by a combination of the semi-circular canals and visual cues, (d) by a combination of the vestibular system and visual cues.

1 1 . Presbycusis is:

(a) a temporary loss of hearing caused by changes in pressure, (b) a natural loss of hearing with age, (c) a loss of hearing which can be corrected through medication, (d) a persistent ringing in one or both ears.

12. One of the functions of the inner ear is that of balance which is achieved through:

(a) the vestibular system which comprises the semi-circular canals and the otolith organs, (b) the vestibular system which comprises the cochlea and the otolith organs, (c) the vestibular system which comprises the otolith organs and the ossicles, (d) the vestibular system which comprises the cochlea and the ossicles.

1 3. The part of the vestibular system which senses linear accelerations is called:

(a) the cochlea, (b) the semi-circular canals, (c) the otolith organs, (d) eustachian tube.

1 4. If a pilot is flying with a head cold or similar infection the subsequent inflammation may cause the eustachian tube to become blocked and the pilot may be subjected to:

(a) a temporary loss of hearing, (b) vertigo, (c) a loud and persistent ringing in the ears, (d) severe pain during a descent.

1 5. Over-stimulation of the vestibular system may result in:

(a) motion sickness, (b) a temporary loss of hearing, (c) a blocked eustachian tube, (d) ringing in the ears.

1 6. During a sudden deceleration a pilot may experience a pitching down sensation. This is known as:

(a) the inversion illusion, (b) the oculogravic or somatogravic illusion, (c) the elevator illusion, (d) the leans.



THE EARS - QUESTIONS Page 4-03

1 7. During a sudden acceleration a pilot may experience a pitching up sensation. This is known as:

(a) the inversion illusion, (b) the leans, (c) the elevator illusion, (d) the oculogravic or somatogravic illusion.

1 8. The sensation, which may be felt by a pilot, that an aircraft is turning when the wings are in fact level is called:

(a) the inversion illusion, (b) the leans, (c) the elevator illusion, (d) the oculogravic or somatogravic illusion.



CHAPTER 5

A. INTRODUCTION

THE EYES

THE EYES Page 5-1

Of the five senses, vision is the most commonly used and although, from the pilot's point of view, perfect vision is not necessary, good functional vision is. There are various aspects concerning vision that are important to pilots and so a basic understanding of the physiology and limitations of the eye is important.

B. PHYSIOLOGY

The eyeball is approximately 23 mm in diameter and is protected in a bony socket in the skull. Six small muscles, attached to the skull and the eyeball, move the eye up and down, from side to side and also allow it a small twisting movement. The main components are:

Fovea Iris

Blind spot

Pupil

Cornea

Lens

Retina Optic nerve

Figure 5.1: Anatomy of the eye

1 . THE CORNEA

This is a transparent window of about 1 0 - 1 2 mm which seals the front of the eye and allows light to pass through it. The surface of the cornea is curved and so some refraction, or bending, of the light rays takes place, but since the shape is fixed and no muscles are attached to it the refractive abilities cannot be altered. Protection of the cornea is achieved by the eyelids, the movement of which aids the lubrication process.

2. THE IRIS

The iris, a pigmented or coloured muscular membrane, is situated behind the cornea and contains an aperture known as the pupil. The iris is the first means of enabling the eye to adapt to changing light conditions. In the case of poor light conditions the iris contracts thereby increasing the size of the pupil and allowing more light through. The reverse occurs in very bright light conditions.

3. THE LENS

The lens, located immediately behind the iris, is supported by the ciliary muscles which are used to change its shape, thus enabling it to focus the light rays. The lens is curved on both sides, much like the lens of a magnifying glass, and as the muscles relax the lens flattens thus reducing the curvature of its surface resulting in less refraction, or focusing, of the light rays. The opposite occurs when the muscles contract and squeeze the lens which increases its curvature, thereby increasing the amount of focusing. This would occur when focusing on an object close at hand.

This mechanism is known as accommodation, a function which tends to decrease with age as the lens becomes less flexible, a problem that can of course be corrected by wearing glasses. Tiredness or fatigue will also influence the ability to accommodate, resulting in blurred images.



5. THE RETINA

THE EYES Page 5-2

The retina, a soft transparent layer of light-sensitive nervous tissue, is located at the rear of the eye. It contains two different types of photo-receptor cells, known as rods and cones. Nerve fibres link these photo-receptor cells, combining in a small area of the retina as the optic nerve. In this area there are no photo-receptors and it is known as the blind spot.

CONES

These are concentrated around a small central area of the retina, which is directly opposite the lens, called the fovea. The cones, which are highly sensitive to colour and for defining small detail as well as distant objects, provide the best visual acuity or accuracy. They achieve maximum efficiency in conditions of good illumination, becoming less effective in poor light and darkness. Since our direct vision is focused in the foveal region, cones are important for our central vision.

RODS

The primary function of the rods is to define movement, but not in detail and, having no perception of colour, only in shades varying from black to white. They are located in areas away from the fovea, are able to function in dim light and are thus instrumental in our peripheral vision, the function of which is essential for both orientation and night vision.

C. VISUAL ACUITY

Visual acuity is the measure of a person's ability to see. It is expressed as the distance at which a person can clearly see an object, relative to the distance at which a person with normal vision can clearly see the same object. The term 6/6 (m), 20/20 (ft) vision means that a person can, at distance of 6 metres (20 feet), clearly see the same size of character that a normal observer can also see at a distance of 6 metres (20 feet) . Greatest visual acuity occurs when the retinal image is focused on the fovea and reduces substantially towards the periphery. Physiological factors which will affect visual acuity include the quality of the cornea, the efficiency of the lens and the sensitivity of the retina, whilst other influences include the size of the object, both the direction and level of illumination as well as the contrast between the object being observed and the background. Although peripheral vision is sensitive to movement, an object must be looked at directly in order to distinguish detail.

D. REFRACTIVE ERRORS

Refraction is the ability of the cornea and the lens to bend light rays in order to focus them on the retina to produce an image. Refractive errors consist of:

HYPERMETROPIA (Long sightedness)

This occurs when the refractive power of the eye is too weak. As a result the cornea and lens are unable to focus an image on the retina. The actual point of focus would occur beyond the retina. This can be a natural defect, but can also be expected to occur in older people. Fortunately it can be corrected by wearing convex lenses.

MYOPIA (Short sightedness)

In this case the refractive power of the eye is too strong and light rays are focused in front of the retina. This can also be corrected, but in this case concave lenses will need to be worn.

ASTIGMATISM

This is an optical effect caused by unevenness of the curvature of the cornea and to a lesser extent, the lens, resulting in distorted images. This error can be corrected by the use of various lenses.

PRESBYOPIA (Age changes)

In most people, near vision deteriorates with age due to changes in the lens, making it less pliable and therefore reducing the process of accommodation. The first sign of this condition is difficulty in reading fine print in poor light. It can be improved with the use of corrective lenses.



E. MONOCULAR AND BINOCULAR VISION

THE EYES Page 5-3

These terms refer to the use of one eye (monocular) as opposed to the use of two eyes (binocular) by the same person. Whilst not necessarily considered essential for flying, there are distinct advantages in having both eyes available for vision other than just having one.

By focusing both eyes on the same object at the same time light rays will enter the eyes at different angles resulting in different images in both eyes. This is due very simply to the fact that the eyes are located some distance apart from each other, and can be easily experienced by looking at an object with each eye in turn. Far from being a problem, the brain uses this information to estimate the distance of objects; the greater the difference between the two images, the closer the object is.

At the same time, the problem of the blind spot is eased due to the fact that light rays from the same source cannot fall simultaneously on each blind spot. The object will be seen by one eye and the information passed to the brain.

F. VISUAL FACTORS AFFECTING THE PILOT

1 . COLOUR VISION

Although normal colour vision is not necessarily essential for a pilot, the abil ity to distinguish between red, white and green is, especially in respect of compliance with night flying regulations. Total colour blindness is quite rare, current estimates have it occurring in less than 0.1 % of the population, but between 5% and 1 0% of males have difficulty in distinguishing between red, green and white, whilst up to 20% may have a degree of colour deficiency. Increasing age may cause yellowing of the cornea and lens and may decrease the intensity of blue light. It is known that smoking and alcohol also have an adverse effect of colour vision. There is no cure for this deficiency.

2. NIGHT VISION

Physiologically, night v1s1on is achieved through the rods because of their greater sensitivity. Greatest night visual acuity is achieved by looking slightly off-centre at an object, due to the fact that rods are concentrated away from the centre of the retina. Maximum night efficiency of the rods may take as much as 30 minutes to achieve and therefore a period of dark adaptation may be necessary to acquire good night vision. A very brief exposure to bright light requires a further period of adaptation and a good policy for pilots is to close one eye before exposure to bright light in order to retain good night vision in that eye. Factors which can adversely affect night vision include mild hypoxia, smoking, alcohol, stimulants, minor ailments and increasing age.

3. GLARE

Glare can be caused by high altitude flight, flying just above a layer of cloud or directly into a low sun. The contrast in the levels of brightness outside and inside the cockpit may make it difficult for the pilot to read the instruments or displays and result in him flying blind without realising it. Good quality sunglasses are a necessary requirement in this kind of environment.

4. DEPTH PERCEPTION

Depth perception, or the ability to judge distance, requires many cues. The texture of an object becomes more obvious as it comes closer, which assists in judging height; the clarity of an object provides clues as to its distance - in hazy or misty conditions an object becomes blurred making it more difficult to judge its distance and the relative movement of an object, which appears to move faster the closer it becomes also plays a part. So too, does binocular vision, with although beneficial is not necessarily essential since a person with one eye can also use the cues mentioned to assist in determining distance.

5. EMPTY FIELD MYOPIA

Myopia means short-sightedness and this case is caused by flight at high altitude or at night, when there is nothing to look at. The eyes tend to adopt a resting focus at a point approximately two metres away, with the result that a distant object has to be fairly large in order to be seen, an obviously dangerous situation. This can be overcome by actively re-focusing the eyes on distant objects such as the ground, clouds or stars.

6. CONTACT LENSES

These are often used in preference to traditional spectacles and have certain advantages, in that they provide better peripheral vision and are not subject to misting. However, for the pilot there are certain associated problems of significance. The cornea, not having its own blood supply, obtains



THE EYES Page 5-4

oxygen from the ambient air. Contact lenses can reduce this and cause mild hypoxia and corneal damage as a result. Dehydration in the eye can also occur as a result of low humidity in the cockpit, further damaging the cornea. Cabin decompression can also cause a bubble between the contact lens and the cornea.

7. RADIAL KERATOTOMY

This is a minor surgical procedure on the eye by which certain refractive errors, particularly myopia, can be corrected by making shallow incisions into the cornea. It does result in a substantial weakening of the eyeball structure and may also give rise to unstable refraction. It is, therefore, not acceptable in airline transport pilots and may result in the grounding of even a private pilot for several years.

G. I N FECTIONS AND DISEASE

Given the importance of vision for the pilot, a knowledge of, and treatment for, infections and disease of the eyes is useful. Some of the rnore obvious include:

CONJUNCTIVITIS

The conjunctiva is the lining of the inner surface of the eyelids and the exposed surface of the eye, can become irritated and inflamed by exposure to bacterial or viral infections and irritants such as smoke and dust. The symptoms are a painful burning or stinging sensation and bloodshot eyes, which can be exacerbated in the dry air of an aircraft cockpit. Eyesight can be affected and the eyes become more sensitive to light. This infective form of this disease (bacterial or viral) is very contagious and pilots should refrain from flying whilst suffering from it. Treatment is usually by antibiotics and the problem should clear within a few days.

CATARACTS

A cataract is the slow and painless clouding of the clear lens of the eye. As such it will affect vision because it prevents light from reaching the retina. More often it is a product of the ageing process and can successfully be treated by surgery, following which special glasses will have to be worn.

STY

This is a fairly common problem, especially in children. It is caused by an infection forming a cyst in the tear ducts or hair follicles which can cause a swelling and reddening of the entire eyelid. If necessary it can be surgically removed.

GLAUCOMA

This fairly common disorder is a result of increased pressure within the eyeball due to the inadequate drainage of excess aqueous fluid, which if untreated can damage the optic nerve and lead to a partial or complete loss of vision. It tends to occur more often in elderly people and can be hereditary. Treatment is usually in the form of eyedrops although surgery may be necessary in some cases. Symptoms include eye pain, headache and blurred vision.

H. O PTICAL ILLUSIONS

A pilot operating in an environment which provides limited visual cues, ie full or partial IMC or at night, and at the same time is subjected to stress, owing perhaps to fatigue or the nature of the conditions he encounters, will be apt to perceive what he wishes to perceive, even to the extent of supplying an illusory perception. This condition manifests itself in a number of ways:

(a) FALSE HORIZON

Common during flight in partial IMC, the pilot observes sloping cloud formations, an obscured horizon, or at night, a combination of stars and ground lights, and geometric ground light patterns, all of which present an illusion to a disorientated pilot of not being correctly aligned with the true horizon. As a result, the pilot may place the aircraft in an incorrect, and thus potentially dangerous, attitude.

(b) GROUND LIGHTING

Many pilots, especially in unfamiliar areas, have mistaken lights along a straight road or on a moving train, as approach or runway lights. The judgement of distance may also be affected by bright runway and approach light systems. The illusion is that of less distance to the runway and the natural result is a high approach. Similarly, when flying over a relatively unlit area, the lack of lights reduces height cues and the pilot may fly a low approach.



(c) AUTOKINESIS

THE EYES Page 5-5

This is an il lusory phenomenon that makes a static light appear to move when stared at for a period of 8 to 1 0 seconds in a dark environment. The cause of this phenomenon is, as yet, not known.

(d) LANDING ILLUSIONS

Most pilots have, at some time or other, been exposed to these illusions, which can be divided into three areas of concern:

1 . The initial judgement of the approach slope; 2. Maintenance of the approach slope; 3. Judgement of ground proximity prior to touchdown.

Setting up the initial approach slope can be greatly assisted by the use of aids such as PAPI and VASIS lighting systems. However, there will be many occasions when the aids are not available and the pilot must rely on his own judgement. This obviously improves with experience, although experienced pilots may still be caught out. The following common illusions are described:

(i) RUNWAY WIDTH

A very narrow runway may create the illusion that the aircraft is, in fact, higher than it is. This can result in the unsuspecting pilot flying a lower approach with the possibility of hitting obstacles in the approach path, or even landing short. The opposite can occur with a very wide runway, with the result that the pilot may flare too soon and land hard, or overshoot completely. Both situations are exacerbated at night.

(ii) RUNWAY OR TERRAIN SLOPE

A runway, or terrain, that slopes up may create the illusion that the aircraft is higher than it is. This can result in the pilot again flying a lower approach with its inherent risks. A down sloping runway, or terrain, will create the opposite effect resulting in a high approach.

(iii) FEATURELESS TERRAIN

The absence of ground features, such as dark areas, water, etc can create the illusion of being higher than the aircraft actually is, resulting in a low approach.

(iv) ATMOSPHERIC

Rain on the aircraft's windscreen distorts the pilot's vision, creating the illusion of being higher. Haze may result in the pilot thinking he is further away than he actually is. Both of these illusions may result in flying a lower approach. Flying through fog creates an illusion of pitching up and if this goes unrecognised the pilot may steepen the approach quite dramatically with possible disastrous consequences.



QUESTIONS


1 . The best night vision is achieved by:

THE EYES - QUESTIONS · Page 5-01

(a) looking directly at an object to ensure maximum exposure of the object to the cones, which are more efficient for night vision,

(b) looking slightly off centre at an object, which will allow the rods greater exposure due to their concentration away from the centre of the retina (fovea) ,

(c) regular, brief exposure to light. (d) looking directly at an object to ensure maximum exposure of the object to the rods, which are

more efficient for night vision.

2. In order to allow more light to enter the eye:

(a) the iris contracts, which increases the size of the pupil, (b) the iris expands, which increases the size of the pupil, (c) the ciliary muscles contract, which improves accommodation, (d) the ciliary muscles expand which increases the size of the pupil.

3. Long sightedness, or hypermetropia:

(a) can be corrected only by surgery, (b) can be corrected by wearing convex lenses, (c) can be corrected by wearing concave lenses, (d) can be compensated for by the iris which contracts allowing more light to enter the eye.

4. Rods in the human eye are:

(a) unable to function in dim light, (b) used for central vision, (c) used for the perception of colour, (d) used in peripheral vision.

5. Good night vision is dependant upon:

(a) cones, which are effective in poor light, (b) rods, which are able to function in dim light, (c) accommodation, which increases the size of the pupil, (d) the iris which expands to increase the size of the pupil.

6. Spatial disorientation, a condition in which the subject is unable to perceive his position, attitude and motion relative to the earth:

(a) is most commonly caused by long term exposure to a hazardous noise environment, (b) can be immediately reversed by referring to the aircraft flight instruments, (c) is caused by middle ear infections involving the cochlea, (d) is easily cured by closing the eyes and allowing the vestibular system to correct itself.

7. A reduction in the supply of blood to the retina may result in:

(a) hypermetropia, (b) myopia, (c) empty field myopia, (d) tunnel vision.

8. Empty field myopia refers to:

(a) a condition where the eyes adopt a resting focus at a point approximately 2 metres away, (b) a condition caused by a reduction in the supply of blood to the retina, (c) long sightedness, (d) a condition in which the subject is unable to perceive his position, attitude and motion relative to

the earth



9. A concave lens is used to:

(a) correct for long sightedness, (b) compensate for tunnel vision, (c) correct for short sightedness, (d) correct for empty field myopia.

1 0. A convex lens is used to:

(a) correct for long sightedness, (b) compensate for tunnel vision, (c) correct for short sightedness, (d) correct for empty field myopia.

1 1 . The term "accommodation" is used to describe:

THE EYES • QUESTIONS Page 5-02

(a) the contraction or expansion of the iris in controlling the amount of light entering the eye, (b) the contraction or expansion of the ciliary muscles which changes the shape of the lens, (c) a condition where the eyes adopt a resting focus at a point approximately 2 metres away, (d) a condition caused by a reduction in the supply of blood to the retina.

1 2. When flying an approach to an unfamiliar runway a pilot may unintentionally:

(a) fly a low approach on a downward sloping runway, (b) fly a high approach on an upward sloping runway, (c) fly a high approach on a narrow runway, (d) fly a high approach on a downward sloping runway.

13. When flying an approach to an unfamiliar runway a pilot may unintentionally:

(a) fly a low approach on a downward sloping runway, (b) fly a high approach on an upward sloping runway, (c) fly a low approach on a narrow runway, (d) fly a high approach on a narrow runway.

1 4. When flying an approach to an unfamiliar runway where there is an absence of ground features a pilot may unintentionally:

(a) fly a low approach, (b) fly a high approach on an upward sloping runway, (c) fly a high approach, (d) fly a high approach on a narrow runway.

1 5. At night when a stationary light appears to move if it is stared at it is known as:

(a) an inversion illusion, (b) autokinesis, (c) the oculogravic illusion, (d) hypermetropia.



CHAPTER 6

A. I NTRODUCTION

PRESSURE

PRESSURE Page 6-1

The reduction of pressure with altitude and its effects on respiration have been discussed. There are, however, other effects that the decrease, or increase for that matter, have on the human body and in a profession that requires constant changes in altitude and therefore pressure, it is important that the pilot be familiar with them.

B. THE GAS LAWS

The gas laws with which we are concerned, are the following:

1 . BOYLE'S LAW

At a constant temperature, the volume of a given mass of gas is inversely proportional to the pressure to which it is subjected. In other words, as the pressure reduces, the gas expands.

2. DALTON'S LAW

The pressure exerted by a mixture of gases is equal to the sum of the pressures which each would separately exert if it alone occupied the space filled by the mixture.

Put another way, pressure is exerted by all the gases in a mixture. Partial pressure is the term used to describe the pressure exerted by any one of the gases in the mixture. Our concern is with the partial pressure of oxygen (P02), as it affects oxygen uptake by the body. See Chapter 3.

C. EFFECTS OF PRESSURE CHANGE

Essentially, there are three effects on the body brought about by pressure change with altitude. These are Hypoxia, Barotrauma and Decompression Sickness. Hypoxia has been covered in Chapter 3.

1 . BAROTRAUMA

The body contains a number of gas filled cavities that can be described as either closed, ie, no communication with the outside environment such as the gastro-intestinal tract, or semi-closed, ie communicating directly or indirectly with the outside environment, eg lungs, ears and paranasal sinuses.

EFFECTS OF CHANGING PRESSURE ON CLOSED CAVITIES

(a) THE ALIMENTARY CANAL

In normal, healthy individuals, the stomach and intestines contain between 0 and 400 ml of gas. This is mostly derived from swallowed air, from the action of bacteria within the bowel and from exchange with the gases in the tissues and the blood. During ascent, the gas contained within the stomach expands and usually escapes upwards and out of the mouth. Gas bubbles within the large bowel usually combine to form large bubbles which are vented through the anus. Some discomfort and even severe pain may be experienced. Usually it only becomes a problem at over 25 000 ft and no damage due to expansion has ever been recorded. Passengers who have had recent bowel surgery should not fly until at least ten days after the operation.

(b) THE TEETH

Tiny pockets of air behind fillings, especially in unlined fillings, may expand during ascent, leading to severe pain, known as aero/barodontalgia.

EFFECTS OF CHANGING PRESSURE ON SEMI-CLOSED CAVITIES

According to Boyle's Law, as the pressure on a gas decreases, so the volume increases. During ascent in an aircraft, the pressure on the human body decreases and the gas trapped in the various cavities will expand. Where there is unrestricted communication between a gas filled cavity and the outside atmosphere, gas expansion will occur without difficulty or discomfort, ie wind is passed, ears "pop" etc. If however, the gas remains trapped in a cavity the expansion can cause considerable discomfort and pain, which may cause damage to tissues or organs



PRESSURE Page 6-2

and even incapacitate the individual. One of the most common examples is that of the middle ear.

(a) MIDDLE EAR

The middle ear cavity communicates with the outside atmosphere through the Eustachian tube to the throat. As altitude is gained the expanding air in the middle ear escapes through the Eustachian tube thus equalising the pressure on either side of the ear drum. On descent, the process is reversed, but it is here that problems often occur. The lower, or inner, two thirds of the Eustachian tube is soft walled and this makes it act like a one way valve. If air is prevented from entering the middle ear, the unequal pressure can cause a distortion of the ear drum leading to pain and possible injury. This is known as otic barotrauma. An active opening of the tube is therefore required to allow air to flow into the middle ear and this can be achieved by swallowing, yawning and jaw movements. The problem is exacerbated by an upper respiratory tract infection which may cause the lumen of the tube to narrow. Assistance in opening the tube may be accomplished by a Va/sa/va or equalising manoeuvre, ie blowing air out with the mouth closed and nose pinched. However, in some cases even this fails to equalise pressure and barotrauma results with what can only be described as excruciating pain, which can result in damage to the ear drum. It is interesting to note that most problems in this case occur as the 9000 ft mark is passed.

PREVENTION

This can be best be achieved by not flying when the pilot has a head cold, or at least having a doctor check that the Eustachian tube is functional. The side effects of decongestants and antihistamines make these unsuitable for use by active pilots.

(b) THE PARANASAL SINUSES

These are cavities in the bones that form the upper part of the face.

During ascent and descent, the expanding and contracting gas within the sinuses is free to communicate with the gas in the nasal cavity. If, however, the mucus membrane lining the connecting passages becomes inflamed and swollen as a result of illness or infection, the normal ventilation of the sinus may be prevented, especially during descent, causing severe pain which is often accompanied by watering of the eyes. This is called sinus barotrauma. Damage to the lining may occur, with subsequent bleeding into the cavity. Nasal decongestants may help with ventilation of the sinus cavity.

EFFECTS OF CHANGING PRESSURE ON THE LUNGS

Large volumes of gas in the alveoli, the relatively narrow passages which connect the alveoli to the external environment and the susceptibil ity of the lung tissue to damage combine to make the lungs a vulnerable part of the body. However, the decompression has to be extremely rapid before damage occurs and, provided the individual breathes out during the decompression, is quite rare.

2. DECOMPRESSION SICKNESS

Although decompression sickness is a rare occurrence in pilots now, it was not uncommon in the days of high altitude operation without pressurisation. It is painful, can be dangerous and even fatal.

At sea level, the body is saturated with inert gases, 80% of which is nitrogen. When altitude is increased, some of this nitrogen comes out of solution as bubbles. The symptoms of this condition may vary depending on the site involved, ie the lungs, bloodstream, brain/spinal chord or joints. In the case of the latter, bubbles forming in the joints cause an aching pain commonly referred to as "the bends". The most commonly affected joints in aviation are the shoulder, the elbow, the wrist, the knee and the ankle. Any movement, even rubbing, of the joint aggravates the pain, whereas descent will usually resolve the problem. Other indications include:

(a) The "creeps", which is caused by nitrogen bubbles in the skin and is accompanied by itching.

(b) The "chokes", which creates pain in the chest and a dry cough. (c) The "staggers", which effects the nervous system and results in loss of muscular

co-ordination, partial loss of vision or paralysis of a limb. (d) Collapse, which may occur even after descent, progressing to unconsciousness and death.

Factors which may lead to decompression sickness may include:



PRESSURE Page 6-3

(a) Altitude. Generally an unpressurised altitude in excess of 25 000 ft is required, although it can occur at less.

(b) Duration. The longer the exposure, the greater the risk. (c) Age. There is a greater risk in older people. (d) Weight. Fat people are more susceptible. (e) Diving. Thanks to pressurised aircraft, decompression sickness is rare whilst flying.

However, flying shortly after diving can be fatal. Descending 30 ft in water is equivalent to an increase of 1 atmosphere of pressure. With scuba diving, compressed air is used and this forces more nitrogen into the body. On ascent, this may come out of solution and result in decompression sickness. The situation is drastically worsened should the individual climb into an aircraft and gain substantial altitude.

The South African Civil Aviation Regulations, 1 997, Part 91 , require a period of 24 hours to elapse before flying following scuba diving by flight crew members.



QUESTIONS


1 . I n order to avoid decompression sickness:

PRESSURE • QUESTIONS Page 6-01

(a) pilots may fly in unpressurised aircraft immediately after scuba diving provided the flight remains below 1 0 000 ft,

(b) pilots may fly in pressurised aircraft immediately after scuba diving, (c) pilots should not fly within 12 hours of scuba diving, (d) pilots should not fly within 24 hours of scuba diving.

2. The valsalva manouevre is a procedure which can be used to:

(a) relieve the effects of vertigo, (b) equalise the pressure between the inner ear and the outer ear, (c) prevent spatial disorientation, (d) equalise the pressure on either side of the ear drum.

3. Boyle's Law states that at a constant temperature:

(a) as the pressure of a gas reduces, the gas expands, (b) as the pressure of a gas increases, the gas expands, (c) pressure is exerted by all the gases in a mixture, (d) gas expansion occurs only with a decrease in altitude.

4. Dalton's Law states that:

(a) as the pressure of a gas reduces, the gas expands, (b) as the pressure of a gas increases, the gas expands, (c) pressure is exerted by all the gases in a mixture, (d) gas expansion occurs only with a decrease in altitude.

5. Dalton's Law states that:

(a) as the pressure of a gas reduces, the gas expands, (b) the pressure exerted by a mixture of gases is equal to the sum of the pressures which each

would separately exert if it alone occupied the space filled by the mixture, (c) as the pressure of a gas increases, the gas expands, (d) at a constant temperature, the volume of a given mass of gas is inversely proportional to the

pressure to which it is subjected.

6. The "bends" is a symptom of decompression sickness which is characterised by:

(a) an aching pain in the joints, (b) an itching skin, (c) pain in the chest, (d) difficulty in muscular co-ordination.

7. The "creeps" is a symptom of decompression sickness which is characterised by:


8. The "staggers" is a symptom of decompression sickness which is characterised by:




PRESSURE • QUESTIONS Page 6-02

9. The "chokes" is a symptom of decompression sickness which is characterised by:


1 0. Blowing air out with the mouth closed and the nose pinched:

(a) is not recommended as a means of equalising pressure between the middle and inner ear because it may damage the ear drum,

(b) is a procedure called otic Barotrauma and will assist in equalising pressure between the inner and middle ear,

(c) is called the valsalva manoeuvre and will assist in equalising pressure between the inner and middle ear,

(d) is called the valsalva manoeuvre and will assist in equalising pressure between the outer and middle ear.

1 1 . Decompression sickness is caused by:

(a) nitrogen gas bubbles forming in the bodie's tissues, (b) an excess of carbon dioxide in the blood stream, (c) overbreathing, (d) a decrease in the partial pressure of oxygen.



CHAPTER 7 ACCELERATION AND VIBRATION Page 7-1

ACCELERATION AND VIBRATION A. INTRODUCTION

The pilot is assailed by both of these factors in varying degrees and forms throughout his flying career and apart from the nuisance effect, they have a considerable, if not serious effect, on his performance.

B. ACCELERATION

Speed, even very high speed, has no effect on the human body, whereas acceleration or deceleration (rate of change of velocity) may produce very considerable effects. Principally, four different tissues are affected, namely, the soft supporting tissues, the bony skeleton, the organs suspended in body cavities and the body fluids. All are subject to physical laws and effects can vary from complete collapse of the cardio-vascular system to a simple increase in the fatiguing characteristics of flight. Man is generally ill-equipped to withstand severe acceleration stresses and a good knowledge of these forces and their effects is necessary to understand the effects they produce.

1 . PHYSICAL CONSIDERATION

In aviation, acceleration is usually expressed in multiples of the acceleration of gravity, or G, or 9.81 m/sec2• Thus, if we talk of 2 G, it is in fact 2 x 9.81 = 1 9.61 m/sec2•

2. MOTION AND FORCE

NEWTON'S FIRST LAW

Unless acted upon by a force, a body at rest will remain at rest and a body in motion will move at a constant speed in a straight line.

NEWTON'S SECOND LAW

Acceleration is directly proportional to the force applied if mass is constant.

NEWTON'S THIRD LAW

To every action there is an equal and opposite reaction.

For example, when an aircraft suddenly accelerates forward, it is the inertial force (opposite equal force) which forces the pilot back into his seat. In every case in which man is accelerated (except gravity) , the sensation of increased weight and the redistribution of the blood and displacement of organs, occur in the direction of the inertial force.

3. WEIGHT

Weight is the force exerted by the mass of an accelerating body. The importance in aviation of weight is that when a mass of one kilogram is acted upon by a force which produces an acceleration of 29.43 metres/second', that is, an acceleration of 3 G, it weighs 3 Kilograms.

4. TYPES OF ACCELERATION

(a) LINEAR ACCELERATION

Example: take-off and landing, i .e constant direction with increasing or decreasing speed.

(b) RADIAL ACCELERATION

Example: aircraft manoeuvres such as fixed rate turns, that is, a constant change of direction with a constant speed.

(c) ANGULAR ACCELERATION

Example: spins; that is, where there is a continuous change in direction and speed.



5. EFFECTS OF ACCELERATION ON THE BODY

(a) CARDIO-VASCULAR

ACCELERATION AND VIBRATION Page 7-2

A disturbance in the distribution of blood volume and perfusion results. The immediate effect of positive acceleration is therefore an accentuation of the pressure gradients which normally exist (owing to gravity) in the system in an erect man. Thus, pressures above heart level decrease and pressures below heart level increase relative to what they normally are. This hydraulic effect on the blood results in an accumulation of blood in the lower parts of the body, particularly in the abdominal region, leading to reduced return to the heart and also reduced flow to the brain.

(b) VISION

The visual system is the most sensitive, as blood pressure in the retinal artery must exceed 20 mm Mercury before blood will flow through the retinal vessels. Visual disturbances produced by positive acceleration are caused by decreased blood flow to the retina. The various degrees of grey out are due to progressive decreases in the flow of blood to the retina. Tunnel Vision results when the blood supply to the periphery of the retina fails. Black out occurs when the blood pressure at eye level falls below 20 mm Mercury and blood flow in the retinal artery (and hence blood flow to the retina) ceases.

(c) LIMBS AND ORGANS

Positive acceleration is perceived as an increase in weight and it becomes more difficult to move the limbs, whilst organs may be displaced from their normal positions.

(d) RESPIRATORY SYSTEM

Exposure to positive acceleration of up to 5 G causes little respiratory problems.

6. NEGATIVE ACCELERATION

This is unpleasant and dangerous. The feeling of heaviness and interference with limb movement are similar to those of positive acceleration. The specific effects occur primarily in the head and neck. Exposure produces a sense of fullness and pressure in the head which may lead to a severe throbbing headache. There is marked congestion of head and neck. Exposure for some seconds produces swelling of the eyelids and small haemorrhages in the skin of the face and neck. The lower eyelids may be moved upwards covering the eyes and causing a condition known as red out. Congestion of the lining of the air passages may cause difficulty in breathing and nose- bleeds may occur. The conjunctiva of the eyes become suffused and reddened and blurring of vision can occur. Exposure exceeding 4-5 G for longer than 6 seconds causes mental confusion and unconsciousness. The increase in arterial pressure can cause a slowing or change in rhythm of the heart rate. Exposure to negative acceleration produces an upward displacement of the diaphragm and reduces lung volume and ventilation.

C. VIBRATION

Vibration in any environment can at best be considered a nuisance. Vibration and aircraft are synonymous. It occurs in various forms, often at frequencies of which the person is unaware but could adversely affect body functions. The frequency of vibration is measured in Hertz (Hz). I n aircraft vibration is usually created by the propulsion system as well as the airframe dynamics. The effects of vibration on the human body are summarised in the following table:

HERTZ EFFECT

Up to 1 Hz Motion sickness

1 - 2 Sleep inducing

3 - 4 Progressive fatigue and discomfort

5 - 8 Speech and respiration become difficult

8 - 9 Vibration is felt as fluttering

9 - 12 Difficulty with speech and vision

1 2 - 20 The effect resembles the response to exercise - increased effort in breathing, chest pains and backache.



ACCELERATION AND VIBRATION - QUESTIONS Page 7-01

QUESTIONS


1. Positive acceleration may produce very considerable effects on the body:

(a) only if it exceeds 5 G, (b) most notably on the respiratory system, in excess of 2 G, (c) especially on the eyes, where reduced vision may occur owing to a reduction in blood

pressure, (d) especially on the lungs if it exceeds 2 G.

2. A progressive decrease in the flow of blood to the retina of the eye as a result of positive g will initially cause:

(a) grey out, (b) red out, (c) black out, (d) motion sickness.

3. The condition "red out" in the human eye is likely to occur:

(a) as a result of positive g manoeuvres, (b) as a result of negative g manoeuvres, (c) as a result of exposure to continuous vibration, (d) if the flow of blood to the periphery of the retina reduces.

4. Failure in the flow of blood to the periphery of the retina of the eye as a result of positive g will lead to:

(a) grey out, (b) red out, (c) dizziness, (d) tunnel vision.

5. The term "grey out" is applied to:

(a) the gradual loss of consciousness during high g manoeuvres, (b) the feeling of heaviness in the limbs during positive g manoeuvres, (c) the initial condition which results from a decrease in blood flow to the retina of the eye, (d) the progressive fatigue and discomfort associated with constant vibration.

6. The effect of sustained negative g on the human body is that:

(a) it causes a downward displacement of the diaphragm increasing the volume of the lungs, (b) the lower eyelids may be moved upwards covering the eyes causing a condition known as red

out, (c) there is a decrease in the flow of blood to the eyes, (d) there is an increase in the flow of blood to the retina causing tunnel vision.

7. The effect of positive acceleration on the human body is that:

(a) there is a decrease in the flow of blood to the brain, (b) blood pressure below heart level decreases, (c) there is an increase in the flow of blood to the retina resulting in tunnel vision, (d) it causes an upward displacement of the diaphragm decreasing the volume of the lungs.



CHAPTER 8

A. STRESS

1 . DEFINITION

FLYING AND HEALTH

FLYING AND HEALTH Page 8-1

Stress is the logical result of an overload of mental and/or physical pressure and can be divided into either physical or emotional stress. Physical stress can be caused by prolonged physical discomfort, such as flying an aeroplane through turbulence for any length of time. With regard to flying, emotional stress is considered to be the more important of the two and can be broadly categorised as either acute or chronic. Stress inducing factors are referred to as stressors.

2. CATEGORIES OF STRESS

Acute stress is considered to be relatively short-term and occurs as a result of immediate demands placed on the body such as, in the aviation context, unexpected weather conditions necessitating an unplanned diversion to an alternate airport, or in other words some form of flight deck crisis. Once you have landed it usually disappears. Chronic stress is more serious, is longer lasting and may be brought about by both positive and negative events, such as a birth, marriage, death of a close friend or family member, divorce or concern over employment security or health, or in other words the product of an entire lifestyle. Whilst both of these stress conditions will impact on your flying performance, if they are present simultaneously your ability to handle a situation will be aggravated.

3. STRESSORS

These are generally placed in three categories:

(a) Physical

This comprises environmental conditions such as extremes of both temperature and humidity, lack of oxygen, noise and vibration.

(b) Physiological

This includes sleep deprivation (fatigue}, hunger which may result in low blood sugar, the discomfort of a full bladder or bowel, a mild infection, for example flu, or pain, for example chronic back ache.

(c) Emotional

These are usually associated with social interaction; problems related to the home and work environment.

4. STIMULATION AND STRESS

It is a generally accepted principle that in order to act we need a stimulus and this often takes the form of pressure: we tend to react to demands. The danger is not so much the demand but rather how we cope with it. Our ability to handle stress varies from person to person, but there are a number of factors which determine our response:

(a) Health

Is the person well rested, well nourished, in good physical condition with a happy and relaxed personal life.

(b) Personality

Is the person outgoing, confident and able to make decisions easily.

(c) Preparation

Has adequate pre-fl ight preparation been completed.

(d) Intelligence and aptitude

Is the person right for the job.



5. THE STAGES OF STRESS


The human response to sudden demands is almost instinctive and is often referred to as the "fight or flight" response. The reaction comprises three stages:

(a) The Alarm Stage

The immediate reaction to a stressor is to either confront it or flee from it. Stimulation of the pituitary gland by the brain causes the release of hormones which in turn trigger the adrenal glands into releasing adrenaline into the blood stream. The effect of adrenaline is to increase the heartbeat, the rate of breathing and blood sugar levels. At the same time it is common to experience improved vision, hearing and muscular strength - all of which may be necessary requirements for the solution to the alarm.

(b) The Resistance Stage

The body enters a recovery cycle and starts to repair the damage either physiologically or by adapting to the new situation (learning to cope) or because in most cases physical and emotional stress is only short term. No doubt you will already have recognised these first two stages simply because you will experience them many times during your life. The third stage is where things can start to go wrong.

(c) Exhaustion.

If the body is continually subjected to a stressor it will remain in the alarm stage for a prolonged period of time. Aviation related examples include bad weather experiences without an instrument rating, concern over the reliability of the power plant and insufficient fuel. A prolonged alarm condition means that the body may eventually be unable to keep up with the demands placed on it and exhaustion results. In this condition control is lost because the mind is unable to keep a correct perspective of matters and in really extreme cases the victim may simply give up further attempts at a solution and abandon themselves to fate.

For the pilot, the ability to recognise and manage stress is vital.

6. AROUSAL

Your abil ity to cope with a particular task depends mainly on your state of arousal. The point was made earlier that in order to react we need a stimulus, for example a sudden fright or an urgent need to respond. Factors which contribute to a low level of arousal include boredom, sleep deprivation (fatigue) and even low body temperature. Symptoms of under-arousal such as apathy and being too casual result in poor performance. Factors which are associated with a high level of arousal include fear, panic and lack of confidence. This over-arousal, a result of being too tense, can also lead to poor performance. Optimum arousal and therefore your "abil ity to cope", lies somewhere between the two with a condition of lower arousal being more suited for complex tasks which, by their nature, require a calm approach. A state of higher arousal would be suited for simple, more energetic tasks.

7. ANXIETY

This is a condition which usually results from excessive worry. Symptoms vary from a sense of unease to apprehension and even fear. The net result is poor performance, during which the following signs may be displayed:

(a) Physical.

Perspiration, breathing difficulties, nervous twitches, dry mouth, stomach pains, headache and an increased heart rate.

(b) Behavioural.

Impulsiveness, mood changes from being light-hearted to depressed, sudden changes in emotion, laughing when it is inappropriate, being over co-operative, impatience, unwarranted anger, being rude, smoking, drinking and even eating excessively.

(c) Fatigue.

Being extremely tired from lack of sleep and/or over-worked and/or chronically stressed.

(d) Mental.

Poor concentration and judgement, incorrect thought process, forgetfulness.




This condition, brought about by a chronic stress overload, is dangerous for pilots for all the obvious reasons and should not be taken on board the aircraft. If it is not possible to address the cause yourself, seek medical assistance. But do not fly.

8. RECOGNISING AND MANAGING STRESS

The physical and behavioural symptoms of stress manifest themselves in anxiety. Once you have recognised them it is important to confirm whether they are actual signs or merely perceived because of an unexpected situation. Evaluation of these pressures may reveal that they are not as extreme as originally thought and that you can, in fact, handle them confidently. In terms of stress management it is perhaps best to discuss the two types of stress separately.

ACUTE STRESS

This is the easier of the two to address. The simplest solution to a feeling of stress is to take a short break and relax. From the pilot's point of view this is not always possible whilst flying, in which case slow deep breathing may help you to relax, take stock and view things from a different perspective. Very simply, make time. It would be foolish, if not unnecessary, to commit to an approach in IMC if you are not ready for it. Stay in the hold where altitude and time are on your side. To this end you can also prepare in advance to handle a stressful situation. If the flight is going to terminate with an approach in IMC, plan ahead. Setting the aircraft up, reviewing the arrival and approach charts well in advance are procedures which should be taught to you as part of your instrument rating preparation not merely as good airmanship aspects but also so that you will not be shocked into the approach, trying to do everything at once and subjecting yourself to an unnecessary amount of stress. Being prepared in advance in this manner will also help you should an emergency also arise.

CHRONIC STRESS

This is a far more serious situation arising from more long-term issues. Treatment will most probably be long-term and may include a substantial change in lifestyle and possibly even employment. They key is not to ignore the situation until it becomes serious, but to approach it in a dedicated and serious manner in consultation with your marriage partner, family members, a doctor, counsellor, employer or priest. Talking about the problem with people who can offer advice and support is the first step. A common approach to chronic stress is the "total body approach", which takes into consideration six aspects of well-being: physiological, nutritional, environmental, emotional, spiritual and lifestyle values, all of which are interrelated in terms of both creating stress (negative) and coping with it (positive) . For example a bad diet or poor eating habits can lead to weight problems and lack of energy, which in turn can increase your stress levels. Reduced energy results in low productivity levels at both work and home which in turn increases the pressure to achieve certain tasks, (more stress) whilst the inability to achieve them can lead to a reduction in self-esteem which may ultimately lead to an imbalance in your lifestyle. It now becomes a vicious spiral as the stress increases, the appetite declines and so the cycle continues. Once a positive approach to coping with stress has commenced a slow reversal process commences and one positive effort will have a positive effect on others. The biggest problem is to summon the will to make the change. Physiological and nutritional aspects present an ideal starting point. Exercise, relaxation and a good diet (avoiding alcohol and drugs) will revitalise the body giving it the energy required to start to deal with the stress. Environmental action includes examining the places where you work and live and the people involved in both. Vacations and more time off are methods which are suitable for relieving stress. As a last resort changing jobs, moving to another area or terminating a relationship may have to be considered. Emotional action basically means adopting a more positive approach to life and instead of negative attitudes, like complaining, become more pro-active. For many people an active spiritual involvement provides the peace of mind necessary for stress management, and lastly slow down, do things in moderation, relax and take time for yourself.

9. INCORRECT STRESS MANAGEMENT

Ego can be our biggest enemy. We are all subject to stress, it is a necessary catalyst for action. The person who claims they are less affected by hypoxia than anyone else is probably the same person who believes they do not suffer from stress. This same person may try to avoid stress by ignoring it, or by resorting to alcohol, drugs or medication - which may relieve the symptoms but not the cause. Clearly they are unacceptable methods of dealing with stress. These are referred to as defence mechanisms and may be joined by other subconscious actions designed to remove unwanted or painful matters from our consciousness. Generally, they include:

1 . A lack or awareness, a condition where the brain subconsciously refuses to recognise a stressor. 2. Anger, which may include bad language and even violent behaviour. 3. Imaginary sickness as a means of avoiding reality. 4. Daydreaming, where the mind wanders off into a more comfortable realm to avoid reality. 5. Trying to rationalise or justify incorrect actions, more often these are excuses. 6. Giving up, accepting whatever outcome presents itself.




By their very nature, these will not solve or reduce stress: more probably they will exacerbate it.

B. FATIGUE

1 . DEFINITION

Fatigue can best be described as a very deep tiredness. It can be caused by the same factors which lead to stress and can also be divided into two types.

2. TYPES

(a) Acute Fatigue

This condition can occur as a result of intense and undivided mental concentration, or physical activity, over a prolonged period. The cure is relatively straight forward: a restful and uninterrupted natural sleep, uninfluenced by alcohol or drugs.

(b) Chronic Fatigue

This condition occurs over a longer period as a result of lack of sleep, excessive workload, stress and even jet lag. It cannot be as easily cured as acute fatigue, requiring a prolonged recovery period and in some cases the removal of the root cause. The laws regarding flight and duty time are regarded as a preventative measure.

3. SYMPTOMS

One of the worst features of fatigue is the inability to recognise it, probably due to the symptoms. Some of the more obvious signs include:

(a) Obvious tiredness: slow and frequent yawning, drooping head. (b) Decreases awareness resulting in a lack of response. (c) Much slower reactions. (d) Irritability. (e) Poor concentration: particularly noticeable in instrument flying. (f) Forgetfulness. (g) Being unable to sleep. (h) Reduced short-term memory, forgetting clearances. (i) Making more mistakes. (j) Loss of appetite and increased reliance on alcohol and drugs such as caffeine. (k) Mood changes, erratic behaviour and aggression.

4. PREVENTION AND TREATMENT

The most obvious method of prevention is adequate rest and sleep, combined with a proper balance between work and rest - one of the underlying principles of flight and duty time regulations. However, a proper, balanced diet and exercise also play an important role. You should avoid excessive caffeine, alcohol and cigarettes as a means of either relaxation or as a pick-me-up.

C. SLEEP

1 . INTRODUCTION

Sleep is the body's method of re-charging and re-vitalising itself and the amount and quality thereof ultimately determines how well we can perform both mentally and physically. The average person requires eight hours of restful sleep, or if you like a ratio of one hour of sleep is required for two hours of activity, although it should be noted as a fact that women require more sleep than men!

2. STAGES OF SLEEP

Studies of sleeping subjects, during which the electrical activity of the subjects' brains was monitored by an electroencephalogram (EEG) have shown that sleep periods are made up of two types of sleep. One type is called rapid eye movement (REM) sleep or paradoxical sleep and the other, non-REM or orthodox sleep.

(a) REM Sleep.

This commences some 90 minutes after falling asleep and is characterised by the sleeper's eyes moving rapidly back and forth beneath the closed eyelids. REM sleep is closely related to wakefulness, due to the high frequency electrical waves which occur during this condition where,




although the body is relaxed, the brain activity is similar to a person who is awake. REM sleep is believed to be the sleep period which rejuvenates the brain.

(b) Non-REM/Orthodox Sleep

This comprises four distinct stages:

Stage 1 is the transition between waking and sleeping and is characterised by decreasing brain wave activity, slow rolling eye movements and can last from 1 to 1 0 minutes. Stage 2 sleep continues for approximately 1 0 minutes during which brain wave activity declines still further. Stages 3 and 4 are referred to as slow wave sleep which is characterised by very low frequency brain waves and is thought to be associated with physical restoration.

These types of sleep occur in cycles which have been defined by electronically monitoring brain activity, eye movement, muscle tension and heart rate. The sleep cycle is repeated up to 30 times throughout a long sleep period, with the REM stage recurring approximately once every 90 minutes increasing in length as the period of sleep progresses.

3. SLEEP PATTERNS

Sleep patterns and requirements vary from individual to individual as well as according to age. Older people tend to require less sleep, but usually on a more regular basis. Overall the eight hour rule generally applies - during a twenty four hour period we require eight hours of sleep, although it is a fact that some people require only six, others ten. Night is usually the time during which we sleep, but the body can condition itself to sleeping regularly at any time of day or night. It is, of course, not always possible to receive the full quota of sleep, perhaps due to shift or work duties. In this case the body is able to function on less sleep, but unless the deficit is made up performance will reduce. Disturbed sleep patterns, caused by whatever reason, result in a deficiency of REM sleep symptomised by mental tiredness. However, during the next sleep period the body will change the sleep cycle to increase the portion of REM sleep. A full sleep period of, say, eight hours will provide what is called sleep credits for sixteen hours of activity, after which time the credits are now zero, you will feel tired and your energy levels low - the body is telling you to sleep. If the sleep period is delayed you will now enter a sleep deficit, resulting in a decrease in alertness and performance. This deficit can be countered by a longer sleep period than the normal eight hours. It is not possible to sleep "extra" in order to build up additional sleep credits for an extended period of activity, after eight hours the body will tend to wake up. Shorter than normal sleep periods result in less sleep credits and although this may be countered to some extent by a short nap, the recovery rate of sleep credits is slower.

4. SLEEPING PROBLEMS

There are several sleep disorders which may affect the human body, the most common being insomnia, or the inability to sleep. There are different types of insomnia:

(a) Nervous Insomnia

The most common of all and probably one to which we are all subjected at some time or other. Its cause is based in the anticipation of some near-future event, perhaps an exciting one in the case of children, or in the case of aircrew perhaps a major flight test. Sufferers will experience disrupted sleep for a few nights and recovery from any tiredness is fairly quick.

(b) Situational or Acute Insomnia

This is the result of a disturbance in body (circadian) rhythms, also referred to as jet lag, as a result of travel or even shift work. Again recovery is relatively easy and achieved naturally within a few days.

(c) Clinical or Chronic Insomnia

This is difficulty in sleeping in normal circumstances when the body requires sleep. The victim can be affected for weeks or even months and will most probably require medical attention.

Other disorders associated with sleep include:

Narcolepsy

A condition in which the sufferer falls asleep at any time, even during a situation which requires their full attention. Naturally this would preclude the sufferer from pursuing flying as a career.



Sleep Apnoea


This condition causes a temporary cessation in breathing resulting in the sufferer waking up frequently and being deprived of meaningful sleep.

Somnambulism

Sleep walking.

5. SLEEPING, DRUGS AND ALCOHOL

The use of drugs, with regard to sleeping habits, is confined to two areas: either to stay awake (delay the onset of sleep) or to go to sleep (advance the onset of sleep).

The most common and easily obtainable sleep-delaying drug is caffeine which is present in coffee and to a lesser extent tea.

Sleep inducing drugs come from a group known as benzodiazepines, examples of which include Valium, Magadan, Librium and Normason. As with all drugs, there are two characteristics which are important to its use; the drug's half-life (the time taken for the drug level in the blood stream to fall to half of its peak value) and its effect on performance which is particularly important in the case of pilots.

Alcohol, being a central nervous system depressant, gives the impression of giving one a deep sleep when in fact it does not. Both the REM sleep and mental rejuvenation will be retarded, you may awake earlier than normal and will most probably not feel too fresh! As such, it is not an ideal method to relax and induce sleep after a flight.

6. SLEEP MANAGEMENT

Clearly, sleep is a vital part of our well-being and should be managed carefully with the emphasis on natural sleep rather than on drug-induced sleep. This will involve proper rostering in both normal and long distance flight operations. From the personal point of view certain methods of sleep hygiene should be adopted to ensure a good and meaningful sleep.

(a) Be relaxed. Avoid strenuous physical, or mental, exercise, alcohol, caffeine and large meals before going to bed.

(b) Environment. A comfortable bed in a dark, quiet room at a pleasant temperature with fresh air are ideal.

(c) Maintain a regular sleep schedule.

D. CIRCADIAN RHYTHMS

1 . INTRODUCTION

Despite the legal requirements of flight and duty time, the commercial and operational factors of aviation in today's world are such that air crew are subjected to a disruption of their normal regime, including sleep rhythms and patterns, with a resultant detrimental effect on their performance.

2. BODY RHYTHMS

The human body is exposed to universal rhythms almost from birth. Examples include the earth's rotation of the sun - 365 days, the moon's cycle - 28 days, the tidal cycle - 1 2'h hours and most significantly the earth's rotation of 24 hours which is our basis of timekeeping.

The body has several built in biological clocks which control specific physiological processes, exhibit regular rhythmic fluctuations and are not under voluntary control. These rhythms have cycles of approximately 24 hours and are termed circadian rhythms from the Latin circa (approximately/about) and dia (day) . Experiments, during which all time cues are removed, have produced evidence that the human free running cycle is in fact closer to 25 hours, but because of external factors including day and night, social activities, clock watching and even meal times, the body cycle has become tied to a twenty four hour cycle. These factors which provide our time cues are referred to as zeitgebers, from the German zeit (sight) and geber (giver). and include such things as established wake-up times for work (alarm clock). toilet habits, set breakfast and other meal times, bus, train and aeroplane departure times, the time that we finish work, the continual reference to a watch or clock and even television programme times. All of these, plus many more, serve to align the body with the 24 cycle strongly influenced by the sun - daylight is time of wakefulness, whilst night and darkness are signs that it is time to sleep.



3. RHYTHMS AND PERFORMANCE


Human performance is at its lowest between 0300 and 0600 and at its best between 1 200 and 2000 hours. This is a reflection of the influence of the 3 most important circadian rhythms, ie the sleep/wake rhythm, body temperature and hormone secretion rhythms. An individual's abil ity to perform is directly related to the rise and fall of their circadian rhythms. Of all the body's rhythms, the sleep/wake rhythm is the easiest to change, whilst the body temperature rhythm is very difficult to alter and as such is often used as a reference against which other cycles can be compared. The body's temperature has been found to rise steadily during daytime reaching a peak during early evening before falling during the night to its lowest level at around 0500. Temperature can be linked to performance; high temperatures encourage alertness and good performance, whilst a low temperature is associated with drowsiness and reduced mental performance. It follows, then, that the sleep/wake cycle is also associated with the body temperature cycle since low temperatures encourage drowsiness and therefore sleep. As the body temperature begins to rise it encourages the body to wake up. It should be noted that although the sleep/wake pattern may be disturbed, the temperature pattern remains the same. For example, if you wake in the very early hours of the morning for work, the low body temperature associated with this time of day will result in reduced performance. The performance cycle, associated with both sleep/wake and body temperature cycles can, however, be modified if you are well rested, in good health, well motivated and practised in such skills as are to be performed. This has particular significance to the night shift worker who has to perform well at times when the body's temperature and sleep/wake cycles are not well suited for it. After a few days of adaptation a new sleep/wake rhythmic cycle will become established, although the peak performance achieved may still not be the same as the day shift worker due in part to disruptions of the sleep period as a result of real world zeitgebers such as daylight and darkness, normal family activities, noisy traffic and neighbours. Disruption of the sleep/wake cycle and other circadian rhythms is particularly significant when crossing time zones.

4. CIRCADIAN DYSRHYTHMIA (JET LAG)

Circadian rhythms are of importance for pilots when crossing meridians or time zones on long flights. Circadian desynchronisation alters the times of best and worst performance, disturbs sleep patterns, thus affecting performance even more, and even affects the normal rhythms of the bowel and urinary system which can further serve as a source of sleep disruption. Travelling westwards and having crossed several time zones, you will now find yourself at a location where the local time differs significantly from your own home time. Aspects such as the rising and setting of the sun and the behaviour of the local population are on local time, which your body clock is not synchronised with. You may feel like sleep, when everyone else is starting to go about their daily business. The question as to what to do about it really depends on the duration of your stay. For most pilots, turn around time is fairly short and does not warrant the resynchronisation effort because most circadian rhythms will only re-synchronise at a rate of about 1 to 1 Y2 hours per day. Thus a time zone change of, say eight hours, may require up to eight days to re-synchronise the body clock. The fact that different circadian rhythms require different periods of time to change can exacerbate the situation as these rhythms are now desynchronised with one another. This phenomenon is known as circadian dysrhythmia, and may result in poor sleep and mental performance, headaches, giddiness and disrupted eating habits.

Flights from west to east tend to be more detrimental than those from east to west due to the fact that when travelling eastwards you are travelling away from the sun, making a day appear shorter than 24 hours. The reverse is the case when travelling westwards since we are now travelling with the sun making a day appear to have more than 24 hours, or if you like more daylight.

The use of drugs such as sleeping tablets and alcohol to induce sleep is strongly discouraged as they are central nervous system depressants, induce abnormal sleep and may remain in the body for long periods of time. A far better regime is to avoid caffeine, daytime napping, excessive mental stimulation, emotional stress, and strenuous exercise before retiring. A comfortable bed in a warm ventilated room with a warm milky drink and a little light reading in bed is possibly the best answer.

E. PILOTS, DRUGS AND SELF MEDICATION

Drugs are basically divided into two categories; the so-called mind-altering hard drugs such as cocaine and LSD, and those used for medicinal purposes which are either prescribed by a doctor or purchased over-the-counter and include sedatives, tranquillisers, drugs for colds, infections and other ailments. Clearly hard drugs and flying do not mix and should not be mixed - a clear head is required in the cockpit. In the case of prescribed drugs, it is important that the prescribing physician be made aware that he is dealing with a pilot as the condition being treated and the possible effects and side effects of the drug may preclude the pilot from flying anyway.

Pilots who self medicate, for example colds and flu, are courting disaster. The condition requiring the medication and/or the medication taken for the condition, may disqualify the pilot from flying. Practically all drugs have side effects. These side effects, usually not critical for the average man in the


©A vex Air Training 1 0/2004


street, could be potentially hazardous to the pilot, eg the requirement to make split second decisions, exposure to hypoxia, abnormal acceleration forces, vibration, as well as conditions causing disturbance to normal vision or vestibular functions. Examples of some over the counter drugs with side effects on the nervous, circulatory, vestibular and other systems are:

Painkillers, decongestants and antihistamines. These can cause drowsiness or euphoria, and impair vision, balance and judgement.

Appetite suppressants. Many of these contain stimulants. Their withdrawal can often cause severe depression in an individual.

Preparations used to avoid nausea and vomiting. These drugs are classified as major tranquill isers, have a sedative effect and can cause blood pressure problems as well as tremors and irregular heartbeats.

Anti-diarrhoea preparations. Most of these contain atropine or codeine (a morphine derivative).

Other so called drugs, some of which may be purchased over the counter, can also cause problems of their own:

1 . COFFEE

Caffeine, found in coffee, is a stimulant and excessive intake can cause tremors and insomnia.

2. ASPIRIN

This can aggravate ulcers and also prolong bleeding.

3. ANTIHISTAMINES

These can cause drowsiness, which is aggravated by the simultaneous intake of alcohol.

4. SYSTEMIC DECONGESTANTS

These usually contain antihistamines and therefore may have a similar effect.

5. ALCOHOL

Besides having addictive potential, it can slow reflexes and induce a euphoric effect removing inhibitions. Chronic long term intake can cause irreversible liver damage, as well as damage to the brain, heart and so on. It is also a diuretic and can lead to dehydration. Organ damage due to excessive alcohol intake can occur before dependence develops and for both reasons alcohol use should be controlled. The currently accepted safe norm of alcohol intake is considered to be 21 units per week for men and 14 units per week for women, where one unit (containing approximately 1 0 gm of alcohol) is the approximate equivalent of 500 ml of beer or a single measure of spirits or wine. Recognition of alcohol dependence or alcoholism includes the following symptoms: secret drinking, shaking, loss of memory, a greater intake required before the effects are noticeable. Treatment includes recognition and acceptance of the illness by the sufferer, a positive attitude, total abstinence and professional counselling.

6. TOBACCO

Tobacco contains the dependence inducing drug nicotine, withdrawal symptoms from which may become apparent within as short a period as 20 minutes and usually present as irritability, aggression and even hostility. Nicotine is also a stimulant which acts on the central nervous system and depresses, or masks, the effects of fatigue. Haemoglobin, contained in the human body's red blood cells, has a great affinity for carbon monoxide, which is contained in tobacco smoke, and thus readily absorbs it into the blood stream in preference to oxygen, which adversely affects the body's production of energy. See Hypoxia. Cigarette smoking is considered a cause of lung cancer and cardiovascular diseases. The modern trend is to ban smoking in passenger carrying aircraft.

As a precaution, it is recommended that pilots consult their Aviation Medical Examiners (AME's) as to the possible side-effects of the medication they wish to take, and if taken the time delay before they are again fit to fly, because with only a few exceptions, the use of all drugs is unacceptable when flying.



MEDICATION IN COMMON USE


A wide range of non-prescription medication is available "over the counter". However, just because it is not a scheduled (prescription) drug, does not necessarily mean it can safely be used by pilots. Any preparations for coughs, colds, flu, sinusitis, hay fever or allergic conditions which contain antihistamines or codeine should be avoided because of their possible side effects. The following are examples of common brand names of prescription and non-prescription drugs available, which should not be used by pilots on active flying duty:

PAINKILLERS

Stilpane, Stopayne, Painrite forte, Betacod, Dolorol forte, Beserol, Betapyn.

DECONGESTANTS

Actifed, Sinutab, Cepacol, Degoran, Dristan.

COUGH MEDICINES

Benylin, Cepacol, Demazin, Linctifed, Phensedyl, Vicks formula 44.

ANTACIDS

Rubragel, Bisma-rex

ANTISPASMODICS

Probanthine, Colofac

ANTIDIARRHOEALS

Lomotil, lmodium

NAUSEA

Stugeron, Avomine

EYEDROPS

Afrin

CAUTION: ALL DRUGS HAVE A LIMITED LIFE AND SHOULD NOT BE USED AFTER THE EXPIRY DATE

The following is a list of some of the medication that may be used by flight crew.



TYPE

1 . Antihypertensive medication

(a) Thiazide diuretics (b) Beta blockers

2. Antigout medication (a) Allopurinol

3. Malaria prophylaxis

4. Oral contraceptive

5. Thyroid supplementation

6. Sodium chromoglycate

7. Cholestyramine

RESTRICTIONS/LIMITATIONS

Must submit a 6/1 2 U+E Only water solube, cardia-selective Beta blockers may be used.

Applicant unfit if symptomatic, or using additional medication

Applicant unfit if any side-effects occur (eg nausea, malaise).

After a 3 month trial period, in the absence of any side-effects

Applicant unfit if any side effects occur

FLYIN G AND HEALTH Page 8-10

Figure 8·1: Safe Medication for Air Crew

F. TOXIC MATERIALS

The nature of flight is such that the pilot is easily subjected to all manner of toxic hazards, some of which cannot be easily eradicated. Possibly the most common is carbon monoxide poisoning, which is present in engine exhaust gas and cigarettes and is colourless and odourless. Haemoglobin has a far greater affinity for carbon monoxide than it does for oxygen and will readily transport carbon monoxide in preference to oxygen. This results in oxygen starvation of the brain and the attendant decrease in mental fitness which can ultimately lead to death. Leaking exhaust systems, or exhaust heat exchangers used to provide cabin heat are ready causes of carbon monoxide poisoning. Symptoms include, headaches, nausea, lethargy, reduced mental agility and ultimately unconsciousness. Relief is obtained by removing the cause and breathing fresh air or pure oxygen. Most manufacturers of piston-engined light aircraft recommend opening the fresh air vents when using cabin heat or windshield de-misters. If fresh air is not available you should land immediately. Fluids carried in the aircraft such as aviation fuel, oil and hydraulic and de-icing fluid all emit vapours which are both irritant and toxic and termination of the flight is the logical solution. Aircraft interiors as well as passenger belongings contain plastic which gives off highly toxic fumes when burning, and inhalation of these fumes is considered to be the most common cause of passenger deaths in aircraft on the ground. Carriage of toxic materials in aircraft is strictly governed by Part 92 of the Civil Aviation Regulations, 1 997.

G. INCAPACITATION

Probably as a result of frequent and extensive medical examinations and a sense of responsibility regarding personal health, sudden incapacitation of pilots is extremely uncommon. We are, however, human and therefore subject to the same ills as everyone else and the degrees of incapacitation that may result.

1 . CAUSES AND SYMPTOMS

(i) Cardio-vascular

Sudden incapacitation and the unconsciousness which may follow, is probably the result of a massive heart attack (coronary thrombosis), which is usually preceded by chest pains and numbness in the arm and ends in unconsciousness.



(ii) Gastro-enteritis

FLYING AND HEALTH Page 8-1 1

This has been identified as one of the more common causes of incapacitation amongst pilots. Accompanied by vomiting, severe stomach pains or cramps, fever, diarrhoea, dehydration and even vision and balance disturbance, this condition can lead to total incapacitation.

(iii) Epilepsy

This is a brain disorder during which there is a disruption of the electrical activity in the brain. Symptoms vary depending on the severity of the attack, which may be described as Major or Minor. A Major epileptic attack, marked by rigidly contracted muscles and convulsions followed by a loss of consciousness, may last from 2 to 5 minutes and is followed by a deep sleep. A Minor epileptic attack usually presents as a lapse of awareness and lasts less than a minute, following which the sufferer continues with whatever they were doing before the attack without realising anything has happened. The condition can occur from a very early age, but can be brought on by scar tissue in the brain as a result of a head injury. Both conditions prevent a person from holding a pilot licence.

(iv) Migraine

The more severe member of a family of headaches. Headaches as such do not involve the brain tissue or the bones of the skull which are, in fact, insensitive to pain. Rather it is associated with the nerves and blood vessels around the brain, as well as certain facial nerves, the mouth and throat, and muscles in the head and neck. Nerves in these areas that become either over stimulated, damaged or inflamed send pain signals to the brain and the victim experiences a headache. The exact cause of migraine attacks is not clear, but contributing factors include reduced blood flow to the brain, low blood sugar, high blood pressure, fatigue, stress, alcohol and flickering lights. Symptoms include severe pain on either one or both sides of the head, nausea and vomiting, loss of appetite, an increased sensitivity to light and sound and may last from a few hours to a few days. Some sufferers experience warning signs prior to the attack, including weakness, mental confusion, tingling sensations in arms and legs, a visual sensation of flashing lines and a blank spot in their vision. This condition may prevent a person from flying.

(v) Faints

Fainting is a condition which causes a loss of consciousness due to a reduction in the supply of blood to the brain, often caused by pooling of the blood in the lower limbs. Healthy people can suffer from this as a result of shock, loss of blood, lack of food and an abnormal posture. Isolated cases, if the cause is known, should not influence medical fitness to fly. If the symptoms are identified before the faint occurs, the person should be encouraged to sit with their head lowered between their knees. If unconscious, the person should be laid on the floor with the legs raised.

Incapacitation can be categorised as either sudden or insidious (gradual).

2. CATEGORIES

(a) Sudden Incapacitation

Unconsciousness brought on fairly rapidly as a result of the causes already mentioned.

In the case of single pilot operations, and providing the pilot recognises the symptoms quickly enough, the immediate action is to ensure the aircraft is at a safe height and flying in a constant direction before engaging the auto-pilot.

(b) Insidious Incapacitation

As the name implies this is more subtle and can occur slowly, so much so that the victim and his fellow crew may not be aware of it. Hypoxia is a classic example.

Pain or illness can be associated with this condition in the form of gastro-enteritis, otic barotrauma, migraine, sinus pain, side effects of drugs and food poisoning. Where the symptoms are recognised before flight then treatment is easy: do not fly. In the air the same action as for sudden incapacitation should be taken.



H . GENERAL HEALTH

1 . COMMON MINOR AILMENTS


This· includes normal day to day illness such as colds, influenza and gastro-intestinal upsets. Pilots who are suffering from any of these are effectively precluded from flying for two reasons; the illness as such will affect performance and the medication, whether prescribed or over-the-counter (OTC) drugs will have side effects which influence your abil ity to perform. The hours gained, the money earned or the perceived prestige is not worth risking your life or the lives of the passengers. If you are sick do not fly.

2. TROPICAL DISEASES

The most common of these result from inadequate sanitation and hygiene and include:

TYPHOID - transmitted by water contaminated by salmonella bacteria from faeces and urine, symptoms include serious bowel problems and fever which can lead to delirium. If not treated it can be fatal. It can be vaccinated against.

HEPATITIS - a viral infection of the liver which can be transmitted by infected water or food but more likely through body fluids such as blood and saliva. Symptoms include tiredness and fever which can lead to jaundice. Vaccination can provide short term protection.

CHOLERA - an epidemic disease spread by food and water contaminated by faecal bacteria. Symptoms include vomiting, cramps and diarrhoea. In particular dehydration can be fatal. Protection is best achieved by boiling water and cooking all food. Vaccination aids recovery but is of little use for protection against this disease.

Other diseases to which we may be subjected are:

MALARIA - a parasitic disease spread by an infected anopheles mosquito is currently the world's biggest killer. Symptoms appear between ten days and two weeks after infection and include headaches, intermittent fever and nausea. Certain areas of the Republic, namely the Lowveld and northern Kwa-Zulu Natal are known danger areas. Prevention can take the form of chloroquine-based medication although it should be noted that certain strains of malaria have become resistant to this type of medication. Pilots should also be aware that some of the medications currently used may have side effects such as headaches, dizziness, gastrointestinal disturbances such as nausea, vomiting and diarrhoea, and even blurred vision. Pilots should consult an Aviation Medical Examiner (AME) regarding the use of malaria prophylactics.

YELLOW FEVER - transmitted by insects and prevented by vaccination, which is effective for ten years and is often a prerequisite for entry into many countries.

Pilots who expect to fly internationally, particularly into Africa, should consult their AME for assistance regarding protection against local diseases which may be encountered.

I . SURVIVAL

In the event of a forced landing or ditching it may be necessary for crew and passengers to survive a period of time before rescue. The priorities in such situations are generally protection, location, water and food. Protection being the most important. The commonest cause of death in these conditions is exposure. Hypothermia in water and cold land conditions and heat exhaustion and dehydration in hot conditions. Common sense dictates the measure that should be undertaken in each of these situations.

Human beings are warm blooded and maintain body temperature very precisely between 36.2'C and 36.9'C. A minimal change in temperature of just a degree up or down will cause major physiological disturbances and drastically affect the individual's ability to function normally. The body uses the majority of the energy it produces to maintain its temperature between these very specific levels. The body is further able by specific means to increase or decrease heat loss, thus further enabling it to regulate its temperature when the external environment is hostile. Should heat loss be excessive in cold weather the body will generate heat by muscular contractions. This method of heat production works well but it is costly in terms of energy stores and can rapidly lead to exhaustion. Heat and therefore energy, can be conserved using additional layers of clothing. Where environmental temperatures are high, the body gets rid of excess heat by shunting blood to the skin where additional heat loss is obtained by convection and sweating. Dehydration rapidly becomes a problem if lost fluid is not adequately replaced. In aquatic conditions, the surrounding water can be very cold, and every effort should be made to get out of the water. Once out of the water, protection from the wind, also a cooling factor, is essential. In sub zero temperatures particular care must be taken of hands and feet to avoid frostbite. In excessively hot and or humid conditions, adequate fluid replacement must take place and all tasks requiring exertion should be left for the cooler part of the day or night.




J. CONTRA-IN DICATIONS TO TRAVEL BY COMMERCIAL AIRCRAFT

The following figures can be used as guidelines in terms of the minimum time interval for passengers between illness or surgery and flying, and even then only essential flights. Pilots may only resume flying duties with their AME's consent.

1 . Within 4 weeks of a heart attack; 2. Within 2 weeks of a stroke; 3. Within 2 weeks of eye, ear, nose or throat surgery; 4. Not at all while the jaw is surgically wired; 5. 2 Weeks after any abdominal or bowel surgery; 6. Pregnancy beyond 240 days or a threatening miscarriage;



QUESTIONS


1 . Acute stress i s considered to be:

(a) of long duration, (b) curable only through medication, (c) directly related to poor diet and obesity, (d) relatively short term.

FLYING AND HEALTH · QUESTIONS Page 8-01

2. In the event of a forced landing or ditching, generally the priorities for survival, in a hostile environment in order of importance, are:

(a) water, food, protection and location, (b) protection, location, water and food, (c) water, protection, location and food, (d) food, location, water and protection.

3. Acute fatigue in pilots is:

(a) best treated by medication to make you sleep, (b) best treated by restful and uninterrupted natural sleep, (c) best treated by not flying for at least 48 hours, (d) incurable.

4. Paradoxical or REM sleep is characterised by:

(a) high levels of brain activity, (b) decreasing brain wave activity, (c) very low frequency brain waves, (d) slow, rolling eye movements.

5. Chronic stress is considered to be:

(a) directly related to poor diet and obesity, (b) curable only through medication, (c) of long duration and may be related to problems associated with lifestyle, (d) relatively short term.

6. The stage of Orthodox sleep known as slow wave sleep:

(a) is characterised by high levels of brain activity, (b) is the sleep period which rejuvenates the brain, (c) occurs every 90 minutes, (d) is characterised by very low frequency brain waves and is associated with physical restoration.

7. The sleeping disorder known as narcolepsy:

(a) is an inability to fall asleep as a result of nervous excitement, (b) would preclude a person from pursuing a flying career, (c) is an inability to fall asleep as a result of a disturbance in circadian rhythms, (d) would not preclude a person from pursuing a flying career providing that a suitable medication is

used.

8. Jet lag, a disturbance in body (circadian) rhythms, often manifests itself in the form of:

(a) acute insomnia, (b) sleep apnoea, (c) narcolepsy, (d) nervous insomnia.



9. Chronic fatigue in pilots:

(a) can only be treated by medication, (b) is best treated by restful and uninterrupted natural sleep, (c) requires a long recovery period, (d) is incurable.

FLYING AND HEALTH · QUESTIONS Page 8-02

1 0. Circadian dysrhythmia, or jet lag, is a disturbance in body rhythms which is more pronounced:

(a) on flights from east to west, (b) on flights from north to south, (c) on all flights which are conducted at night, (d) on flights from west to east.

1 1 . In terms of stress management:

(a) a defence mechanism is the best method of dealing with stress, (b) alcohol is an ideal method of handling stress, (c) defence mechanisms are unacceptable methods of dealing with stress, (d) medication is the only method of dealing with stress.



CHAPTER 9 HUMAN INFORMATION PROCESSING Page 9-1

HUMAN INFORMATION PROCESSING A. INTRODUCTION

Flying an aircraft is an exercise in which the pilot's sensory perception, that of balance, vision, touch and hearing, combined with the decision making process creates the required co-ordinated physical reaction necessary to control the aircraft. The same holds true for a person driving a motor car or riding a bicycle. In order to understand how we process information it is first necessary to have some knowledge of the systems involved in the task.

B. THE GENERAL SYSTEM

1 . THE CENTRAL NERVOUS SYSTEM

THE BRAIN

(a) Function

Earlier we referred to the brain as the body's "computer" and in a l imited sense, this is so. The abil ity to think, speak, judge, reason and learn are all functions of the human brain. But more than just these intellectual activities, the brain also directs our breathing, metabolism, voluntary and involuntary movements, regulates and co-ordinates all the sensory impressions we receive and the emotions we feel.

(b) Location

The brain is housed in a rigid bony skull which provides protection along with three different types of membrane or meninges. A clear colourless fluid called the cerebrospinal fluid surrounds the brain acting as both lubricant and shock absorber and also assists the bloodstream in bringing nutrients to the brain and removing waste products. This latter task is of particular importance in that it protects the brain from contamination by waste products carried by the blood.

(c) Composition

(i) Cerebrum

This, the largest and most highly developed part of the brain, is located in the area immediately under the skull. It is concerned with the more complex functions of the brain such as thought, memory, sensory perception, voluntary movement and as such is the structure which separates humans from other animals. The outer surface of the cerebrum, called the cerebral cortex, is responsible for controlling the sensory organs (eyes and ears) as well as motor activities such as walking and running.

The cerebrum is divided down the middle from front to back into two halves or hemispheres, each of which is responsible for controlling the activities of the opposite side of the body, for example the left hemisphere controls the right side of the body. Although similar in appearance there are very clear functional differences between them, for example the development and use of language, speech and writing is carried out in the left hemisphere, whilst the right hemisphere is responsible for creativity and spatial orientation.

(ii) Cerebellum

About the size of a peach, or roughly one-eighth the size of the cerebrum, the cerebellum is considered the most primitive part of the brain and is responsible for balance, or equilibrium, and muscular coordination.

(iii) The Brain Stem

The brain stem comprises several parts, the functions of which include linking the spinal chord to the higher parts of the brain, controlling the heartbeat, blood pressure, breathing, body temperature, facial movement and sensation, eye muscle control, sex drive, pleasure, pain, hunger and thirst.



THE SPINAL CHORD

HUMAN INFORMATION PROCESSING Page 9-2

The spinal chord is contained within, and thus protected by, the backbone or spinal column which is made up of small bones called vertebrae. Each vertebra is constructed like a solid ring, separated from the above and below vertebrae by a cushioning layer of cartilage called a disc. Attached to the rear of each vertebra is a bony arch-like structure called the spinal canal, within which is housed the very fragile spinal chord. Openings between the vertebrae allow nerves to enter and leave the spinal chord as they pass to and from the arms, legs and trunk. The spinal chord serves as the major link passing messages to and from the brain and the body.

Together, the brain and the spinal chord comprise the central nervous system. See Figure 9-1.

Cerebrum Spinal Chord

Cerebellum

Spinal Chord

Vertebra

(a) Central Nervous System (b) Vertebra and Spinal Chord

Figure 9-1: The Central Nervous System

2. PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system, which connects the central nervous system to the body organ systems, comprises the somatic and autonomic systems.

The somatic system includes sensory nerves which carry messages from the sense organs and other body receptors to the brain for processing.

The autonomic system, or biological control system, includes nerves which are only motor nerves, the purpose of which is to regulate bodily functions such as breathing, sweating, heart rate and the blinking of the eyes. No conscious thought is required for this system to function.

Reflexes are another example of the functioning of both the somatic and the autonomic systems. If you inadvertently touch something which is hot you will automatically pull your hand away without your brain telling you to. It is the link between the sensory nerve, which feels the heat, and a motor nerve, which directs the response.

3. SENSE AND SENSITIVITY

It was the Greek philosopher Aristotle who classified the five senses as sight, sound, smell, taste and touch. Today, of course, we know that there are indeed many more; the more pertinent, perhaps, from our point of view being vestibular (accelerations, balance, gravity) , kinesthetic (the abil ity to detect motion through our muscles, tendons and joints) and the skin's ability to distinguish cold and warmth as well as pain and pressure.

It is through sensory reception that we react to changes in the body's internal and external environment. The body organs associated with the senses contain highly specialised sense cells or receptors which are excited by a particular stimulus. The sensitivity, that is its abil ity to respond to a stimulus, of the receptors in the various organs is different. Photoreceptors {in the eyes) are sensitive to light, mechanoreceptors (in the skin and ears) are sensitive to touch, sound and equilibrium, chemoreceptors (in the nose and mouth) are sensitive to smell and taste, whilst




thermoreceptors constantly monitor the body's temperature. Stimulation of a receptor causes a nerve impulse to be transmitted to the relevant part of the brain where it is processed and interpreted and a response issued.

There are, however, limits to the effectiveness of the various receptors, a sensory threshold below which a receptor cannot detect a stimulus. A common example of this, which is pertinent for pilots, is sound (either very soft, perhaps outside of our frequency range or hearing loss due to age). The sensory threshold serves as an indication of the sensitivity of the sense organs and the testing of eyes and ears forms an important part of the aviation medical examination.

Repetitive stimulation of a receptor can lead to adaptation, a condition where there is a gradual decrease in the response to that stimulus to the extent that you become completely unaware of it. A typical example is wearing a wristwatch, even though it is touching your skin, and may even be fairly tight, you will soon become unaware of it. You may be similarly affected by constant exposure to sound.

C. MEMORY

1 . DESCRIPTION

Memory could be loosely defined as the brain's ability to store and recall information and is considered essential for intelligent behaviour, for without it we would be unable to learn. It is still not fully understood how the memory works, but in simple terms memory storage follows a chemical change between the nerve cells or neurones of those parts of the brain associated with memory -the cerebral cortex, thalamus and hippocampus. Each time we learn something new this chemical change creates new pathways or memory traces, which we can activate at any time to reproduce a memory.

2. TYPES

Whilst we tend to think of memory as just being the ability to recall events, thoughts or facts motor-skill memory is used to learn or remember motor skills such as riding a bicycle, driving a car and, yes, flying an aeroplane. This ability makes it possible for us to perform many functions without conscious thought. Factual memory allows us to recall more complex things such as poetry, identity numbers, telephone numbers, faces of people we knew a long time ago and so on. Basically there are three levels of memory:

(a) Sensory or Immediate Memory

The sheer volume of stimuli to which our senses are subjected means that it is only necessary for the brain to retain these sensory inputs for a few seconds, or just long enough for the brain to decide which of the stimuli to act upon. It is, perhaps, interesting to note each sense has its own memory store and that the time span of each varies, for example a visual image probably lasts for a second, whereas sounds may be retained for as much as eight seconds.

(b) Sort-term or Working Memory

This is the ability to retain information in temporary storage or, if necessary, work with it for a slightly longer period. Whilst in terms of capacity, it is generally agreed that the sort-term memory is able to hold up to seven types of unrelated information, the period of retention appears to vary according to opinion from between 1 0 - 20 seconds, to 30 seconds, to a few minutes. Certainly information decays very rapidly unless we consciously rehearse, or repeat it, or use it. From the pilot's perspective the danger of the short term memory is its inability to retain a lot of information for a long period, which underlines the necessity of writing down, for example, an IFR departure clearance. Another example of the limitation of the short-term memory would be where you are given a telephone number to dial - as soon as you have finished dialling it you will probably have forgotten most of the number unless you continually repeat it in your mind. A method used to try to increase the capacity of the short-term memory is "chunking", or grouping together items of information to remember them as one unit, for example combining both the frequency and identification of a radio navigation beacon as one item, rather than two separate ones. The use of mnemonics is practised in flying to remember checks, for example downwind checks (BUMFFH).

The short-term memory also functions as a working memory in that new information can be actioned or alternatively information can be drawn from the long-term memory for use. In this way, the short-term memory acts as a way station, processing information in an attempt to remember it either by rehearsal (repetition, or rote) or by encoding (understanding or linking new information to some already acquired information) before transferring it to the long-term memory. Encoding or understanding information is deemed the more successful method of retaining



HUMAN IN FORMATION PROCESSING Page 9-4

information. Rehearsal or rote learning, like cramming for an examination, seldom results in long term retention.

(c) Long-term Memory

The long-term memory, the brain's "hard drive", is where the greatest capacity for storing information exists. Here information can be stored for a few months, a few years or an entire lifetime - the capacity almost defies belief. If not used regularly, information stored here does decay with time, although evidence suggests that information is never fully forgotten, it merely becomes more difficult to retrieve. Prior to storage, information is classified into two areas:

(i) Semantic Memory

Semantic or meaning memory deals with the storage of information in word form and is associated with ability and understanding, such as driving a car or flying an aeroplane and the use of language or remembering how to spell a word. Clearly, if we are to store information here we need to understand it, an action that requires concentration and total attention and one that is not the product of rote learning. We can help ourselves by associating new information with that already stored or by learning new information in the environment where it will be practised, for example an experienced flying instructor will suggest to a student that he sits in the parked aeroplane while learning a sequence of checks rather than in a comfortable chair at home.

(ii) Episodic Memory

Episodic or the event memory is responsible for storing events or episodes which have been experienced during our daily lives. It is quite common that such events are not stored completely accurately but are influenced or modified by our own attitudes and expectations. The testimony of a person, who is an expert in a particular field and may have witnessed an incident in his area of expertise, may be coloured by his own opinion of what occurred rather than be an exact account of what actually happened.

3. REMEMBERING AND FORGElTING

Once information has been stored in the memory it can be retrieved or recalled at any time and in different ways. Recollection means that we are able to recover or reproduce information that we have stored in our memory. Another method of using memory is recognition - the identification of information or material that we have encountered previously. It often happens that we might recognise someone's face but are unable to remember their name - a classic example of good recognition but bad recollection. Another example of which is the difficulty in remembering a particular word. These lapses in memory are still not fully understood but serve to illustrate the complex procedures involved in memory storage and recollection. Methods used to improve memory include:

(a) the use of checklists (b) mnemonics (c) practice and repetition (d) association with stored data

Forgetting, which is perhaps considered a bad thing, actually serves an important function and may be classified in three different ways:

(a) The Effect of Time

The natural attrition due to the passage of time. Information which is not used or is no longer useful tends to be discarded.

(b) Interference

This theory suggests that new information which is added to the memory interferes with similar information which is already stored.

(c) Motivated

This refers to the desire to forget something because you want to. Unpleasant or traumatic memories are stored by the brain in a way that makes them difficult to recall and in the process spare you unnecessary mental anguish.



4. AMNESIA


This term refers to the loss of the ability to remember. It can apply to old or new memories, can be total or partial, permanent or only temporary, can be as a result of brain damage, or concussion, disease, drugs or psychological trauma. Most commonly it affects episodic memory only, so that events are forgotten but the person is able to speak coherently. The different types and causes include:

(a) Age

This is a common cause, possibly due to deterioration in the cardio-vascular system which results in too little blood and possibly too few nutrients reaching the brain. Since memories are stored in different parts of the brain it often happens that old memories are retained but more recent events are forgotten. The degenerative diseases of old age are also responsible for deterioration in memory and amnesia. Older men are susceptible to transient global amnesia, which can cause loss of memory for minutes or hours.

(b) Alcoholism

Long term alcoholism results in the gradual deterioration of brain cells and thus memory. Very heavy drinkers are unable to remember the events that took place while they were intoxicated.

(c) Head Injuries

One of the effects of a head injury is temporary amnesia, with the memory loss occurring from the time just before the injury until just after. Usually memory returns as the injury heals.

(d) Classic or Hysterical Amnesia

This is usually the result of emotional stress where the sufferer is so overwhelmed that amnesia provides the escape from reality. The person may believe they are in a strange place, not know their name, from where they come or to where they are going. Invariably, though, they have retained a knowledge of language and social customs.

(e) Other Types of Amnesia

Less common types of amnesia include Auditory Amnesia, in which there is no memory for words and Visual Amnesia, which is the inability to recognise objects that were once familiar and even printed words.

(f) Fugue State

This is a psychiatric condition, which may last from a few days to a few weeks, in which a person suddenly loses all recollection of their personal identity and past life, during the course of which they may move to another area, assume a new identity and employment, totally unaware of any change in their normal existence. Equally suddenly, the condition passes leaving the sufferer distressed and confused as to how they came to be in this new environment and unable to remember anything that occurred while in the fugue state. This conditions tends to affect only those with hysterical personalities, or a background of character disorder, and is generally caused by a very intense emotional experience.

D. INFORMATION PROCESSING

1 . ATTENTION AND VIGILANCE

The abil ity of humans to process information is effectively determined by two factors: the attention span, and the short term memory, with the l imited amount of information which it can retain. The control that we have over our attention is limited and no matter how vigilant we may try to be, we can be easily distracted by other sights or sounds. Human attention can be categorised as follows:

(a) SELECTIVE ATTENTION

This is simply a system of exammmg and prioritising the sensory input stimuli. Those stimuli which are pertinent to the task at hand are retained whilst the remainder just fade away. Stress plays an important role in the retention of stimuli, where stress levels are not too high excess capacity allows the person to be aware of other stimuli such as someone calling you, or in the case of the pilot of an aeroplane, audible warning signals or ATC communication. Where stress levels are high a greater demand is placed on our attention and it is possible that important information can be overlooked or discarded. For example, the pilot of an aircraft joining a very




busy circuit at high speed, trying to look out for traffic, listen to ATC and complete landing checklists arrives on final approach only to find the landing gear still retracted!

(b) DIVIDED ATTENTION

Even though our attention might be focused on one task, it is still possible for other stimuli to intrude and divide our attention. This ability should not be confused with motor programmes which allow us, without conscious thought, to carry out several physical tasks at once, such as walking whilst swinging a walking stick with one hand and eating food held in the other. Divided attention in the thought process is part of a more complex information processing system conducted by the brain. This facility is commonly referred to as the "cocktail party effect", in that if you are in a group of people you might be concerned with one conversation only but still have the capacity to overhear your name being called. It can be both good and bad. The ability to divide our attention is both useful and necessary in many activities and from the aviation point of view is what enables us to carry out secondary tasks, such as changing radio frequencies or aircraft configuration and communicating with ATC whilst still flying the aircraft. However, the negative side is that it allows our mind to wander onto other matters, for example what we might be doing once the flight is over.

2. STRESS AND AROUSAL

Stress and arousal (alertness) tend to go hand in hand. The more stressed we are the more alert to the cause of the stress we are, almost to the exclusion of other events which require attention. This reduction, or even failure, in divided attention is often the cause of mishaps because important information has been missed, for example the gear up warning signal. The ability to divide your attention is an important skill for pilots and generally improves with competence and experience.

3. INFORMATION COLLECTION AND PROCESSING

(a) THE FUNCTION OF THE BRAIN

Commonly referred to as the Central Decision Maker, the brain is central to the human information processing system. Information which is gathered by the senses is transmitted by the nervous system to the brain where it is evaluated, a course of action decided upon or stored as part of the learning and remembering process. We have often referred to the brain as a computer simply because in many respects it functions the same; it has memory, controls functions and systems, and provides solutions to problems. This incredible device has a greater processing and memory capacity than any computer yet built but as a decision maker has a major limitation: it has only a single channel capacity. In other words it is only able to process one thing at a time and the decisions which are arrived at are not simultaneous, but rather a series produced one after another.

(b) STRUCTURE

The method of information processing by humans follows a series of phases which can best be explained by using a model diagram which shows, in simple terms, the sequence of events involved.

Sensory Short term/ Central

stimuli working Decision memory Maker

Action

I Motor programmes

I Feedback :·

Figure 9-2: The Model of Information Processing

(i) THE STIMULUS OR PERCEPTION

This is the first phase in the process and is provided by our senses. These stimuli, or incoming signals, are transmitted via the peripheral nervous system and the central nervous system to the




short term sensory store. At any time during the course of normal daily activity we are faced with a veritable barrage of stimuli, but only that which is pertinent to the task at hand is filtered out, as a function of our attention mechanism (selective), and the rest is discarded.

EXAMPLE

In level flight the pilot, whilst scanning the flight instruments, observes a decrease in height, and a gain in speed.

(ii) PROCESSING OR ANALYSIS

In this, the second phase, the information is now analysed and compared with that already stored in the memory to form a mental model and a decision is made by the central decision maker to either act or file it away in the long term memory (remember), which is how experience is acquired. This process is more commonly known as thinking.

EXAMPLE

By comparison with known conditions stored in the memory, the brain decides that the aircraft's attitude is incorrect (nose low).

(iii) ACTION AND FEEDBACK

ACTION

Once the brain has decided on a course of action it sends out electrical signals via the motor nerves to the appropriate muscles which react in response.

EXAMPLE

Using the elevator the pilot adjusts the aircraft's attitude to the level position.

FEEDBACK

Feedback on the decision (correct/incorrect) is provided by our senses from which further corrective action can be taken.

EXAMPLE 1

The pilot observes that the aircraft has stopped descending and speed is constant, the correct control change was made, no further action required.

EXAMPLE 2

The pilot observes that the aircraft is now gam1ng height and losing speed, from stored information the brain determines that the aircraft is nose high and signals the muscles to respond accordingly.

(iv) This method of information processing, ie receive, process, action, feedback is called the closed loop system since the central decision maker is continually involved in the process because of feedback. Through feedback the response to an action can be identified and, if necessary, further action initiated, as in the examples given, which allows us to maintain continuous control over the operation.

(c) M ENTAL OR MIND SET

One of the dangers of inexperience is expectation or mental set. For example, hearing what you want or expect to hear can influence the perception stage of information processing. The inexperienced pilot who took off on runway 03 and returned to the airfield an hour later expects to land on the same runway and may even approach the airfield to join in an appropriate position for runway 03. Instructions to join for runway 21 were not expected and confusion results. In this case being inexperienced has increased stress levels and the anticipation of a joining procedure, which is good, has lead to a mental set which is not good! Stress has the effect of diminishing perception and explains why radio calls go unanswered and the gear gets left up despite the warning signal.



(d) ERRORS IN PERCEPTION


The correct decision can only be made if the information received is correct. Errors in perception, the process of receiving and analysing information, have already been described elsewhere in this book, and include vestibular and non-vestibular illusions, (see Chapter 4) .

(e) RESPONSE TIME

This refers to the time period between perceiving the stimulus and responding to it. The actual time period depends on just how complex the problem is and whether the brain, as central decision maker, is involved. If the response to the stimulus is through a motor programme only, the response time is very short, but where the response requires conscious thought and decisions by the brain the response time may increase substantially.

4. THE MULTI-FUNCTIONING BRAIN

Although the brain can be accurately described as a single-channel decision maker, its power is such that we are able to carry out a variety of functions at the same time. This is made possible by the different levels of mental activity of which the brain is capable, the most advanced of these being conscious thought or cognition.

(a) THINKING

This is the process of conscious decision making based on information received through sensory stimulus which is analysed and perhaps compared with that which is already stored in the memory (knowledge). following which a decision is made and action initiated.

(b) MOTOR PROGRAMMES

There are many tasks which we perform in everyday day life which have become repetitive to the point that we are able to accomplish them automatically without conscious thought. Such actions are the result of motor programmes, the benefit of which is that, without the need for direct involvement, the brain is able to concentrate on the decision making tasks whilst at the same time we are able to perform other functions simultaneously. Some conscious monitoring will, however, be required. Driving a car, riding a bicycle, walking, speaking and even tying your shoe laces are all examples of motor programmes, but at the same time, however, it should be stressed that a motor programme is only as good as the time spent practising it. If you have not ridden a bicycle for a few years the initial attempt will be shaky, but the skill returns with repeated practice.

Ultimately, some aspects of flying an aeroplane also become a motor programmes. The early stages of flying training require almost total concentration, but as progress is made and new skills are learned and developed by continual practice more space becomes available for other aspects such as using the radio, keeping a navigation log, reading a map and so on. The motor programme for flying is being developed. One of the negative aspects of a motor programme is that without direct or conscious thought they are prone to error or action slips, for example releasing the manual flap lever instead of the park brake prior to taxiing or retracting the gear instead of the electrically operated flaps. Motor programmes such as these are called open loop systems, since the brain is not directly involved and no feedback is given. It becomes clear that some motor programmes require the brain to adopt a monitoring role, or in other words, think before you act.



HUMAN INFORMATION PROCESSING - QUESTIONS Page 9-01

QUESTIONS


1 . A motor programme is an action which:

(a) is accomplished through selective attention, (b) is accomplished through divided attention, (c) required conscious thought, (d) is accomplished without conscious thought.

2. A fugue state is a condition which:

(a) may last from a few days to a few weeks, (b) causes total amnesia, (c) causes memory loss due to the passage of time, (d) allows actions to be made without conscious thought.

3. Semantic memory is memory which deals with:

(a) the storage of events which have occurred during life, (b) the storage of information in word form, (c) the temporary storage of information, (d) chunking.

4. A closed loop system is a method of processing information which:

(a) is used by motor programmes, (b) includes feedback, (c) excludes feedback, (d) stores data in the semantic memory.

5. The task of examining and prioritising sensory input stimuli is a function of:

(a) a motor programme, (b) divided attention, (c) selective attention, (d) semantic memory.

6. The ability to focus on one task but still be alert to other stimuli is a function of:

(a) divided attention, (b) selective attention, (c) motor programmes, (d) adaptation.

7. Information processing which involves action and feedback is:

(a) called adaptation, (b) an example of a motor programme, (c) called chunking, (d) referred to as a closed loop system.

8. The process of grouping together items of information to remember them as one unit is referred to as:

(a) cramming, (b) adapting, (c) chunking, (d) grouping.



HUMAN INFORMATION PROCESSING - QUESTIONS Page 9-02

9. The ability of the short term or working memory to process unrelated information is limited to:

(a) between 1 0 and 20 types, (b) 7 types, (c) 30 types, (d) between 2 and 5 types.

1 0. Chunking is:

(a) the ability to focus on one task but still be alert to other stimuli, (b) the storage of information in word form, (c) a method which can be used to increase the capacity of the long term memory, (d) a method which can be used to increase the capacity of the short term memory.

1 1 . A task which is accomplished without conscious thought is referred to as:

(a) chunking, (b) adaptation, (c) a motor programme, (d) a closed loop system.

1 2. Adaptation is:

(a) a gradual decrease in the response to receptor, (b) the ability to focus on one task but still be alert to other stimuli, (c) an action which is accomplished without conscious thought, (d) stimulation of the short term memory to increase its capacity.



CHAPTER 1 0 HUMAN BEHAVIOUR Page 1 0-1

HUMAN BEHAVIOUR A. INTRODUCTION

Human beings differ from one another not only physically and intellectually, but also in their personality characteristics. It is these differences which not only identify and set us apart as individuals, but in many respects determine how we interact with one another.

B. GENERAL CONCEPTS

1 . PERSONALITY

Personality is the term which is used to describe the characteristics of a person's behaviour, attitude and feelings. It is often a source of attraction between two individuals who recognise in each other those characteristics which are similar to their own. Indeed, each time we meet someone new we either consciously or sub-consciously start to evaluate their personality, identifying those characteristics which largely determine how we will react towards them.

(a) CHARACTERISTICS

The development of a person's personality is considered to start at an early age and many characteristics, such as temperament, extroversion, introversion, aggression, anxiety and independence may, according to opinion, be inherited. Those which remain stable and resistant to change are referred to as personality traits, and are usually already well established by the age of six. Other influences such as environment, family life and culture also contribute. Personality traits are very difficult to change and if an attempt is to be made, intensive psychotherapy would be required.

(b) INDIVIDUAL DIFFERENCES

Personality characteristics and traits form an important part of pilot selection, particularly for multi-crew operation where cockpit conflict must be avoided. Personality assessment takes many forms, from personal interview to written tests or questionnaires which are based on a procedure known as factor analysis. This method involves asking several thousand people a series of questions concerning their opinions, habits, likes and dislikes. Correlation of the responses identifies established patterns in personality characteristics: people who enjoy rave clubs and disco-dancing are hardly likely to be found in a museum or a l ibrary! At the most basic level, personality can be expressed in one of two ways; extroversion/introversion and anxiety.

An extrovert is an outgoing person with recognised traits of being impulsive, dominant, assertive, uninhibited and sociable. The introvert is conservative, cautious and shy. Anxiety manifests itself in extremes from emotional instability to guilt, fear and worry and can apply to both extrovert and introvert. Most people are well balanced and can thus be referred to as average, but as the personality moves further away from this average so the characteristics become more pronounced; above the average - initially stable, responsive and easygoing, becoming more aggressive, anxious and changeable. Below the average - introverted, initially stable, thoughtful and controlled, becoming anxious, sober and pessimistic.

It becomes clear now why certain personalities are better suited to certain types of work; the anxious extrovert is not likely to be an accountant or bank manager, the anxious introvert would probably not be a good salesman. Civil aviation pilots tend to fall into the stable extrovert category, ready to take calculated risks without being impulsive thrill seekers.

(c) ATTITUDES

A person's attitude stems from personal belief, feelings or some knowledge of a subject and is often expressed either as an opinion or by behaviour. Although acquired early in life they are less fixed or rigid than a personality trait and can thus be modified or changed fairly easily by more informed knowledge, or in the case of pilots by extensive training. Almost on a daily basis we are subjected to advertising, political rhetoric, religious preaching, family pressure and a host of other influences all of which can modify or change our attitudes. Pilot attitudes towards cockpit management and risk-taking can be easily modified through training. Crew Resource Management (CRM) training is aimed more at changing or developing attitudes in order to improve team decision making, rather than at changing personalities. Attitudes are measured or assessed by various tests or by interview with the aim of identifying possible hazardous attitudes, of which five have been identified.



(i) The Anti-Authority Attitude

HUMAN BEHAVIOUR Page 10-2

This attitude manifests itself in the person who for no apparent reason dislikes being told what to do and refuses to obey the rules. It is common among a certain type of motorist and dangerous in an aircraft cockpit.

Solution:

Rules are created for a reason and not by some control freak. Too many people fly by the rules and live to retire, for them to be wrong. Accept and comply.

(ii) The Impulsive Attitude

Impulsive people tend to act or react without conscious thought in the belief that something must be done immediately and as a result usually create a bigger problem than they already have.

Solution:

Think before you act.

(iii) The Invulnerability Attitude

The "it will never happen to me" syndrome. This fearless VFR pilot believes there is blue sky at the end of this cloud, a runway to land on and only other people become disoriented and crash aeroplanes.

Solution:

It can happen to you. Accept that as a human being in an aeroplane you are vulnerable and should have a viable alternative course of action.

(iv) The Macho Attitude

This risk taker is not interested in being part of a team because he is better than everyone else put together and will try and prove it. If he is part of a crew and something goes wrong it is everyone else's fault and not his.

Solution:

Learn responsibility. Recognise and accept your limitations.

(v) The Resignation Attitude

Quiet, perhaps withdrawn, this person feels he has no control over his fate, has nothing to offer and goes with the flow. Easily dominated, often threatened, by others who have different opinions, he prefers the role of "Mr Nice Guy".

Solution:

Stand up and be counted. You have a contribution to make. Recognise your own ability.

(vi) Complacency

This is a condition which tends to creep in without the pilot being aware of it. Its cause may be related to confidence created by experience and training. As the pilot becomes more familiar with, for example, a new aircraft type the nervousness or stress associated with learning new systems, performance and aircraft handling dissipates to be replaced by confidence followed ultimately by complacency. One of the symptoms is a reluctance to remain proficient, abandoning good pre-fl ight planning to playing the flight "as it comes".

Bad attitudes can be countered by good attitudes. Part of pilot training involves developing not just flying skills but also the right approach to the task. This includes:

* recognising your own ability and therefore vulnerability; * avoiding actions which become risks because of poor judgement; * obeying the rules; * learning from other people and accepting their opinions; * thinking about and assessing situations before making decisions. * being confident, but realistically so.



(d) BEHAVIOUR

HUMAN BEHAVIOUR Page 1 0-3

The term behaviour defines how we interact with other people which in turn determines how people respond to us: if we are polite and friendly people generally respond in a similar manner. Behaviour types can be categorised as follows:

(i) Aggressive Behaviour

The aggressive person is concerned only with themselves and their own interests, usually at the expense of others. They are argumentative, domineering, abusive and rude and are unsuited for the multi-crew environment where the emphasis is on teamwork.

(ii) Assertive Behaviour

Assertion is a more subtle form of aggression. A person who is assertive is able to manage their concern for themselves without being abusive or having to dominate or ignore another person's rights.

(iii) Submissive Behaviour

Submission expresses your concern for someone else at your own expense. The submissive person either does not express his own opinions or ideas and allows others to dominate him, or alternatively does, but in so apologetically a manner that he is all but ignored.

(iv) Supportive Behaviour

Being supportive means that you can express your concern for someone else without abandoning your own rights and opinions.

In the multi-crew cockpit assertive and supportive styles are ideal requirements.

(f) MOTIVATION

Motivation is the force from within ourselves that drives us to behave in certain ways. Because the product of motivation is reaction it is considered to be a positive force in that at least we are driven to do something. Simple examples of physiological motivation are the drives of hunger, thirst, sleep etc. Psychological drives are more complex; some people are driven by achievement, some by power, others by money or security. Managing or manipulating motivation is viewed as a means of controlling, and therefore improving, performance. In the multi-crew environment, encouraging members to take part in decision making is seen as a positive role in motivation and in turn job satisfaction. Rewards, be it financial or job promotion, are also positive methods of motivating people to perform. Boredom has a negative effect on motivation. A lack of mental stimulus, or interest, poor pay, an apparently meaningless task or being excluded from decision making have the effect of causing complacency and reducing performance.

2. BEHAVIOUR AND SKILLS

The term behaviour can also be used to describe the manner in which we accomplish various tasks. There are three categories.

(a) Skill-Based Behaviour

Earlier we spoke about the brain as the Central Decision Maker and its role in conscious decision making. We also spoke about motor programmes. A motor programme is an example of skil l-based behaviour. By constant repetition or routine we are able to acquire certain skills, which become stored in the skills memory, which we are able to execute without the constant attention of the brain. Certainly the brain will direct that such an action must be taken, but thereafter the motor programme directs the operation. A simple example is lowering the undercarriage in an aeroplane. The brain decides that the aeroplane is in a position where this must be done but concerns itself with other matters whilst the hand reaches for the lever and selects gear down. This ability to be able to carry out multiple tasks simultaneously is extremely beneficial and manifests itself in everyday life. However, it can also be the cause of error. Even though the brain is not controlling the task, ideally it should be monitoring what is happening. In a busy cockpit environment, this is not always possible; you might be trying to complete landing checks whilst communicating with ATC. It is here that mistakes or errors can occur; perhaps selecting flap down instead of gear. This type of error is called an "action slip".

"Environmental Capture" is the term given to another type of error associated with skill-based behaviour and is the result of an often repeated skill, which has become a habit associated with a particular environment. A classic aviation example is the routine "gear down and locked" call




associated with activating the gear lever without the gear actually being lowered. You enter the circuit at a speed above gear extension, you are on downwind and the gear should be lowered but being aware of the high speed you complete downwind checks leaving the gear up. Because this is a motor skill the brain is not monitoring the process and the error goes unnoticed.

By its very nature skil l-based behaviour is so entrenched that it becomes very difficult to modify and conscious thought about the process often upsets the completion of the task. Invariably the skill has to be learnt all over again. Errors associated with it are more common among experienced pilots.

(b) Rule-Based Behaviour

Rule-based behaviours are simply that: sets of rules which are laid down to cater for predictable situations. As such they are stored in the long-term memory and unlike skil l-based behaviour require the conscious involvement of the brain. Simple examples include the forced landing procedure to be followed in the event of an engine failure in the case of a single-engined aeroplane, or the action to be taken in the event of one engine out in a multi-engined aircraft. Such behaviours may be memorised or committed to paper in the form of a checklist to be used in a multi-crew environment and if practised regularly can be considered very reliable providing that the problem has been correctly identified. Legends abound of aircrew shutting down the wrong engine. Another area for errors is having correctly identified the problem to then depart from the procedure established to rectify it.

(c) Knowledge-Based Behaviour

Theoretically the more reliable of the three, knowledge-based behaviour relies on the active involvement of the brain, the use of information stored in the memory as well as that which is obtained from the person's environment. In other words decision-making based on thought and reason. It is what sets us apart from a computer but exposes the human frailty, which can result in error. Factors which can influence this type of behaviour include:

* ambiguous information - misinterpretation can lead to error; * structured thinking and an unwillingness to test or look at information in a different way; * a reluctance to test both positive and negative aspects of an idea; * a tendency to disregard negative aspects of an assumption in preference for positive aspects

(also called confirmation bias) ; * the natural influence on an assumption or conclusion of personal wishes or desires.

3. HUMAN ERROR AND RELIABILITY

It is often said that to make mistakes is human. Any machine, be it human or otherwise, is only as reliable as the component parts: motor cars do break down, the vestibular system can provide false information. Human error is broadly divided into two types; Functional and Cognitive.

(a) Functional Error

This includes items such as:

(i) Error of omission - failing to do something which should be done, e.g. forgetting to lock the door on the way out.

(ii) Error of commission - doing something that should not be done, e.g. putting diesel in your tank instead of petrol.

(iii) Random error - mistakes which do not appear to follow a pattern. (iv) Systematic error - mistakes which do follow a regular pattern.

(b) Cognitive Error

These are errors which are the result of a fault in the thought process and include, false sensations (vestibular), memory lapses, poor judgement, incorrect reasoning and divided attention.

Preventing mechanical errors is achieved by continual testing, for example flight testing. Human errors can be limited by training, maintaining a high level of arousal, monitoring by crew members or equipment such as altitude alert and ground proximity warning systems.



C. JUDGEMENT AND DECISION MAKING

1 . PILOT JUDGEMENT


Pilot error or poor judgement are the two terms most frequently associated with accident or incident reports. Very seldom is an accident the result of poor flying skills. Fortunately judgement can be learned and the first step is to understand what it means. Judgement is the mental process which results in decision making and can be divided into two extreme types:

(a) Perceptual Judgement

This comprises learned skills involving visual perceptions such as judging distance, height or an approach to land, in other words experience. Once the skill has been learned it becomes almost automatic requiring very little thought.

(b) Cognitive Judgement

This is a far more complex process in that it involves thinking. This means taking information from a variety of sources, evaluating it and responding with a course of action. Inevitably the process requires time, there may be alternative courses of action and risk assessment is not easy. To make matters worse, this type of judgement is affected by factors which include stress and fatigue.

Clearly the more time available to think, the less chance there is of error. To this end, training aims at improving the flying tasks which initially require a great deal of conscious attention to the point where they become learned or semi-automatic skills thus allowing the brain more time for cognitive judgement.

2. DECISION MAKING

Decisions are the logical conclusion to cognitive judgement. How good the decision is depends upon a number of factors including experience, your knowledge, your ability to understand and think as well as your flying ability. Good decision making requires the following:

(a) Information

Decide what information is required, collect it, analyse it, compare it with stored information gained from experience.

(b) Facts

Ensure that what you are dealing with are really the facts and not hunches or what you would like to believe.

(c) Alternatives

Always consider alternative courses of action bearing mind the priorities of a situation as well as the advantages or disadvantages of the alternatives. Fuel and weather are two factors which will influence alternative actions.

(d) Action

Once the decision has been made, put it into action with confidence.

(e) Follow Up

Confirm that the response to your action is having the desired effect.

3. SITUATIONAL AWARENESS

Situational awareness means knowing what is happening around you. Given today's advanced navigation equipment and cockpit systems it is very easy to become complacent and assume that everything is normal. In order to maintain a high level of situational awareness the following points should be considered:

(a) Pre-flight planning - the more time spent on the ground planning the flight and considering the options the easier the flight will be, and the easier it will be to make en route decisions.

(b) Make sure that you have all the relevant information, consider it carefully and then decide on a course of action.

(c) Take time to make the decision.



HUMAN BEHAVIOUR Page 10-6

(d) Do not assume, establish the facts. Assumption is the mother of all mistakes. (e) Having decided on and initiated a course of action, check to see if it is producing the desired

results. (f) Force yourself to be alert and avoid distractions. (g) Perhaps most important of all, see things as they are and not as how you want them to be. Plan

for the worst, but hope for the best.



QUESTIONS


1 . Decision making based on thinking is called:

(a) perceptual judgement, (b) cognitive judgement, (c) selective judgement, (d) automatic judgement.

2. Decision making based on experience is called:

(a) cognitive judgement, (b) applied judgement, (c) selective judgement, (d) perceptual judgement.

HUMAN BEHAVIOUR • QUESTIONS Page 1 0-01

3. A tendency to disregard negative aspects of an assumption in preference for positive aspects is an example of:

(a) skil l-based behaviour, (b) perceptual judgement, (c) confirmation bias, (d) submissive behaviour.

4. Avoiding complacency and knowing what is happening around you is an important part of:

(a) situational awareness, (b) cognitive judgement, (c) perceptual judgement, (d) rule-based behaviour.

5. An action slip is:

(a) a situation where a pilot lowers the gear but does not physically check to see if it is down, (b) a situation where a pilot decides to raise the flaps after landing but raises the gear instead, (c) a tendency to disregard negative aspects of an assumption in preference for positive aspects, (d) failing to do something which should be done.

6. The term "environmental capture" is used to describe an error:

(a) such as lowering the gear instead of the flaps, (b) caused by a tendency to disregard positive aspects of an assumption in preference for negative

aspects (c) associated with skil l-based behaviour and is the result of an often repeated skill, (d) such as failing to do something which should be done.

7. The type of behaviour associated with a person who is concerned only with themselves and their own interests, usually at the expense of others is called:

(a) aggressive behaviour (b) assertive behaviour, (c) submissive behaviour, (d) supportive behaviour.

8. When a skill has been learnt by repetition or routine and can be executed without the constant attention of the brain is is regarded as:

(a) rule based behaviour, (b) knowledge based behaviour, (c) functional behaviour, (d) skill based behaviour.



HUMAN BEHAVIOUR - QUESTIONS Page 1 0-02

9. A person who is able to manage their concern for themselves without being abusive or ignoring another person's rights is exhibiting:

(a) submissive behaviour (b) assertive behaviour, (c) aggressive behaviour, (d) supportive behaviour.

1 0. A tendency to disregard negative aspects of an assumption in preference for positive aspects is referred to as:

(a) cognitive error, (b) environmental capture, (c) confirmation bias, (d) situational awareness.



CHAPTER 1 1

ANSWERS CHAPTER 1 - THE AVIATION ENVIRONMENT

1 . (a) 2. (d) 3. (c) 4. {b) 5. {b)

CHAPTER 2 - THE HUMAN MACHINE

ANSWERS Page 1 1 -1

1 . (a) 2. (a) 3. (b) 4. (b) 5. (d) 6. (b) 7. (c) 8. (a) 9. (b) 1 0. (c) 1 1 . (b) 1 2. (a) 13. (d) 14. (a)

1 5. (d) 1 6. (c)

CHAPTER 3 - THE LUNGS

1. (c) 2. (b) 3. (b) 4. (d) 5. (c) 6. (a) 7. (a) 8. (d) 9. {b) 1 0. (c) 1 1 . (c) 1 2. (c) 13. (d) 14. (c)

1 5. (a) 1 6. (d) 1 7. (b)

CHAPTER 4 - THE EARS

1 . (a) 2. (d) 3. (c) 4. (a) 5. (b) 6. (a) 7. (b) 8. (d) 9. (c) 1 0. (d) 1 1 . (b) 1 2. (a) 13 . (c) 1 4. (d)

15 . (a) 1 6. (b) 17. (d) 1 8. (b)

CHAPTER 5 - THE EYES

1 . (b) 2. (a) 3. (b) 4. (d) 5. (b) 6. (b) 7. (d) 8. (a) 9. (c) 10. (a) 1 1 . (b) 1 2. (d) 13. (c) 1 4. (a)

1 5. (b)

CHAPTER 6 - PRESSURE

1 . (d) 2. (d) 3. (a) 4. (c) 5. (b) 6. (a) 7. (b) 8. (d) 9. (c) 1 0. (d) 1 1 . (a)

CHAPTER 7 - ACCELERATION AND VIBRATION

1 . (c) 2. (a) 3. (b) 4. (d) 5. (c) 6. (b) 7. (a)

CHAPTER 8 - FLYING AND HEALTH

1 . (d) 2. (b) 3. (b) 4. (a) 5. (c) 6. (d) 7. (b) 8. (a) 9. (c) 1 o. (d) 1 1 . (c)

CHAPTER 9 - HUMAN INFORMATION PROCESSING

1. (d) 2. (a) 3. (b) 4. (b) 5. (c) 6. (a) 7. (d) 8. (c) 9. (b) 1 0. (d) 1 1 . (c) 1 2. (a)

CHAPTER 1 0 - HUMAN BEHAVIOUR

1 . (b) 2. (d) 3. (c) 4. (a) 5. {b) 6. (c) 7. (a) 8. (d) 9. (b) 1 0. (c)



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