tcas recommendations

TCASRecommendations

Operational Liaison Meeting – Fly-By-Wire Aircraft 2004

Customer Services

TCAS - Recommendations © A

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Contents

• Introduction

• TCAS Presentation

• Resolution Advisory

• Review of TCAS Events

• Recurrent TCAS Questions

• Future TCAS Developments

• Conclusion


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Introduction

• Each year, numerous reports reveal that mid-air collisions are avoided by a whisker.

• Air Traffic Controllers (on ground) strive to avoid such events.

• The onboard Traffic Collision Avoidance System (TCAS)was developed to prevent mid-air collision, particularlyin case Air Traffic Controller guidance is incorrect.

• TCAS II has become mandatory:4Since 1986, in the US4Since 2000, in Europe

• TCAS II has a worldwide ICAO mandate as January 1st, 2003.


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Contents …

• Introduction






• Conclusion


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TCAS Presentation

TCAS:

• Detects any nearby aircraft that is equipped with anATC Transponder.

• Displays potential collision targets.

• Triggers vertical orders to avoid conflict.

Basic TCAS PrinciplesBasic TCAS Principles


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TCAS Presentation …

TCAS II

Mode S Address - Altitude

Reply

MODE SXPDR

Basic TCAS Principles …Basic TCAS Principles …

Interrogation

Interrogation

Reply

Mode S Address - Altitude

TCAS II

MODE SXPDR


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TCAS calculates the:

• Bearing (based on the direction of the received signal)

• Range (based on the time that the signal was received)

• Trajectory and speed (based on intruder position evolution)

• Relative Altitude (based on the signal received)



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PA VOLUMEPA VOLUME

TA VOLUMETA VOLUME

RA VOLUMERA VOLUME

OTHER VOLUMEOTHER VOLUME



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TCAS DisplayTCAS Display

-15

OTHER located 1500 feet below and climbing

PROXIMATE located 1200 feet above and

descending

+12

TA located 500 feet below and climbing

-5

RA located 300 feet above and descending +3


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Contents …

• Introduction






• Conclusion


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Resolution Advisory

• Amidst all the TCAS information, the most importantinvolves Resolution Advisories.

• TCAS calculates two types of Resolution Advisories (RA):

4Preventive Advisory ( “MAINTAIN VERTICAL SPEED – MAINTAIN”):

– Red sector appears on V/S scale, the V/S needle is in the grey area.

– The red square is displayed on the Navigation Display.

– No pilot action on the sidestick (maintain the current vertical speed).

BackgroundBackground


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Resolution Advisory

4Corrective Advisory:– The vertical speed needle is in the red

area.– The red square is displayed on the

Navigation Display


4Follow aural warnings.

4Follow vertical speed green sector on the PFD.


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Resolution Advisory

4Corrective Advisory (e.g. “ADJUST VERTICAL SPEED, ADJUST”):

– TCAS computes the best avoidance maneuver according to a model:

• Assumes pilots reaction within 5 seconds and accelerates with 0.25g in climb or descent until +/-1500 ft/min is reached

• V/S must be maintained until clear of conflict.


Smoothly and firmly follow green sector within 5 seconds


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Resolution Advisory

4Corrective Advisory


TAU

CPA

(Closest Point of Approach)

TAU

Vertical miss distance

« ADJUST VERTICAL SPEED, ADJUST »

Generally:– Deviation caused by a RA maneuver is between 300 and 500 ft– Vertical miss distance at the Closest Point of Approach is around 400 ft


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Resolution Advisory

4Corrective Advisory


Do not overreactDo not disregard a weakening RA

It could create another conflict with another aircraft

TAU

CPA

(Closest Point of Approach)

TAU

Relative altitude

« ADJUST VERTICAL SPEED, ADJUST »


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Resolution Advisory

4Additional Corrective Advisory (E.g.: “INCREASE DESCENT”)

– TCAS computes the best avoidance maneuver according to a model:

• Assumes pilots reaction within 2.5 seconds and accelerates with 0.35g in climb or descent until +/-2500 ft/min is reached

• V/S must be maintained until clear of conflict.


Firmly follow green sector within 2.5 seconds


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Resolution Advisory …

• The following diagram illustrates the number andevolution of RA alerts since 1999 ( Based on Eurocontrol source) :

0

500

1000

1500

2000

2500

3000

3500

1999 2000 2001 2002 2003

RAs alerts

Evolution of RA AlertsEvolution of RA Alerts


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• Statistics in Europe for 2000 ( Based on Eurocontrol source)

0

5

10

15

20

25

30

35

Takeoff Climb Cruise Descent HLD Approach FinalApproach

RAs repartition

Evolution of RA Alerts…Evolution of RA Alerts…

%


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• Statistics in Europe for 2000 ( Based on Eurocontrol source)

4Pilots followed RA in 95% of reported cases4Decision not to follow an RA was based on additional

information:– Intruder visually acquired–Traffic information and/or ATC avoidance being issued by

ATC.

Evolution of RA Alerts…Evolution of RA Alerts…


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• 2003 results are incomplete:4Still missing information from some countries

• Globally, however, the number of alerts is decreasing:4Less reports from pilots4The introduction of TCAS Change 7 reduces the number

of RAs by a factor of 2.

• However, since there are still a significant number of RAs:

Pilots must be well-trained and informed on how to react when faced with an RA TCAS order.

Evolution of RA Alerts …Evolution of RA Alerts …


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Contents …

• Introduction






• Conclusion


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Review of TCAS Events


Always follow TCAS RA orders,even if not in accordance with ATC orders.

• The previously-shown TCAS figures, includes cases where TCAS RA orders were not always followed.

• Some such cases have been reported, and include:4Various missed mid-air collisions.4The tragic “Constance Lake” event of July 1st 2003.


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Review of TCAS Events …

• Aircraft 1 and Aircraft 2 were both at FL 70.

• Aircraft 2 was instructed, late, to descend to FL60.The distance between Aircraft 1 and Aircraft 2 is 5 NM

• The TCAS triggered coordinated RAs:4“DESCEND, DESCEND” RA order for Aircraft 14“CLIMB, CLIMB” RA order for Aircraft 2

• Aircraft 24Followed the ATC order (“Descend to FL 60”)4But, NOT the TCAS order.

• Aircraft 14Followed the “INCREASE DESCENT, INCREASE DESCENT”

TCAS order.

• This induced a new TCAS conflict with Aircraft 3 at FL 50 .

Event N° 1Event N° 1


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Simultaneousvertical and horizontal

crossing at less than 1 NM

FL 70

FL 50

« DESCEND, DESCEND »

RA

« CLIMB, CLIMB »

RA

AIRCRAFT 1

AIRCRAFT 2

AIRCRAFT 3

« INCREASE DESCENT, INCREASE DESCENT »

RA

AIRCRAFT 2descendFL 60.

Event N° 1 …Event N° 1 …


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• The FCOM has been slightly revised to further emphasize the fact that pilots must follow the TCAS order:

The previous FCOM 3.04.34 page:

New FCOM 3.04.34 page (January Revision):

FCOM UpdateFCOM Update


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• Aircraft 1: Was approaching FL 260

• Aircraft 2: Was cruising at FL 270

• Aircraft 1:4Received an “ADJUST VERTICAL SPEED, ADJUST” RA.4Reacted by increasing, rather than decreasing, the

vertical speed.4Reached FL 271, before returning to FL 260

• Aircraft 2:4Received and followed a “CLIMB, CLIMB” RA.

Event N°2Event N°2


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Event N°2 …Event N°2 …

AIRCRAFT 1

FL 270

FL 260

Minimum crossing margin:300 feet, 0.8 NM!!!

« ADJUST VERTICAL SPEED,

ADJUST » RA

« CLIMB, CLIMB »

RA

AIRCRAFT 2


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• Following this event, the FCOM was revised to further clarify the “ADJUST VERTICAL SPEED, ADJUST” RA:

Previous FCOM 1.34.80 page:

New FCOM 1.34.80 page (March Revision):

FCOM Update …FCOM Update …


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• Aircraft 1: Was cleared to FL 370.

• Aircraft 2: Was also cleared to FL 370 by mistake.

• Controller discovered the mistake and instructedAircraft 2 to descend to FL 350.

• Aircraft 1:4Incorrectly interpreted the clearance which was not

applicable to its aircraft4Started to descend.4TCAS issued a “CLIMB, CLIMB” RA.4Did not follow the “CLIMB, CLIMB” RA, as it had visual

acquisition of Aircraft 2.

Event N°3Event N°3


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• Aircraft 2:4Received a coordinated “DESCEND, DESCEND” RA4Followed the RA4Stopped descending, when it noticed that

Aircraft 1 was also descending.

• At the very last moment, Aircraft 1:Performed a sudden and violent escape maneuver, that resulted in injury to flight attendants and passengers.



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« DESCEND, DESCEND »

RA

« CLIMB, CLIMB » RA

AIRCRAFT 2Descendto FL 350.

AIRCRAFT 1 passes slightly below AIRCRAFT 2, with no lateral

separation !!!

FL 370

Order incorrectly

interpreted by AIRCRAFT 1


AIRCRAFT 2

AIRCRAFT 1


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• For TCAS RA orders, the FCOM 3.04.34 was revised to delete the “visual acquisition of the intruder” line.

• For RA Alerts, the FCOM 3.02.34 and QRH TCAS procedures were also revised by deleting the“Attempt to see reported traffic” line.

Previous FCOM 3.04.34 page:

New FCOM 3.04.34 page (January Revision):

FCOM Update …FCOM Update …


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Previous FCOM 3.02.34 page New FCOM 3.02.34 page


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ATC versus TCAS information:

• ATC Radar:4An update rate of several seconds (from 4 to 10).4Altitude data in 100-foot increments.4Sudden vertical maneuvers are not immediately displayed.

TCAS Information is:- Updated 4 to 10 times faster- 4 times more accurate

Additional informationAdditional information

• TCAS:4Interrogates all surrounded transponders every second.4Mode S-equipped aircraft provide TCAS information in 25-foot

increments.


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Visual acquisition limitations:

• At high altitudes, it is difficult to assess:4The range4The heading4The relative height

Additional information …Additional information …

• At low altitudes, it is difficult to assess :4Whether the aircraft is climbing or descending.

• The traffic in contact MAY NOT BE the one that causes the RA to trigger.


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• Other, more or less, serious events have occurred due to the fact that the crew did not follow TCAS orders.

• All such events emphasize the importance of the following:

- Always follow TCAS RA orders.

- Do not try to visually acquire intruders, in case of RA orders.

ConclusionsConclusions


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Contents …

• Introduction






• Conclusion


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Recurrent TCAS Questions

• As of today, the following cases require TA mode selection:

4Engine failure4Dispatch with landing gear down4Known nearby traffic, which is in visual contact4Closely-spaced runways, converging runways,

low terrain along the final approach…

• Recurring questions concerning TA mode selection:

4Emergency descent4Engine failure4Aircraft at its maximum ceiling altitude



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Recurrent TCAS Questions …

• Most often due to rapid decompression.

• Performing an emergency descent in a busy airspace increases the risk of generating traffic conflict.

• A “CLIMB, CLIMB” RA order is not always requested:4An “ADJUST VERTICAL SPEED, ADJUST” RA

can be triggered (decrease the V/S).

Emergency DescentEmergency Descent


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Emergency Descent …Emergency Descent …


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ADJUST VERTICAL

SPEED, ADJUST

DESCEND, DESCEND


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In case of an emergency descent,Airbus does not recommend selecting TA mode.


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• In case one engine fails, the TCAS must be set to TA mode to comply with AC 20-131:

• After an engine failure, aircraft performance is degraded.

• When TA is selected:4Affected aircraft not requested to perform an RA maneuver.4No additional stress generated by a TCAS alarm

in a stressful environment.

Engine FailureEngine Failure


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• Airlines often complain that TA mode is sometimes too restrictive, in particular for the A340-500/600, which is a:4 Powerful aircraft4 Fly-by-wire aircraft, not subject to stall in normal law.

• For the following reasons, it is not recommended tomaintain TA/RA, in case of an engine failure:

4To have a common procedure for all aircraft4If the intruder is TCAS-equipped:

–They will see that you are in TA mode.–They will perform an RA maneuver.

Engine Failure …Engine Failure …


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• In addition:4The ECAM’s ENG SHUT DOWN Procedure requests the crew to

select TA TCAS mode.

Airbus recommends the selection of TA mode,in case of an engine failure.

4Airworthiness Authorities have approved this TA mode selection, in case of an engine failure.

Engine Failure …Engine Failure …


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• AC 20-131A defines the maneuvers that the aircraft must be able to perform.

• In particular, the aircraft must prove that it can respond to a TCAS RA CLIMB order, even whenit is at its maximum altitude.

Aircraft at its Maximum Ceiling AltitudeAircraft at its Maximum Ceiling Altitude


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Time (s)V/S (feet/minute)

Speed (knots)

Aircraft at its Maximum Ceiling Altitude …Aircraft at its Maximum Ceiling Altitude …

Time (s)


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• These graphs show that the aircraft can follow:4A “CLIMB, CLIMB” TCAS RA order (1500 feet/minute)4An “INCREASE CLIMB, INCREASE CLIMB” TCAS RA order

(2500 feet/minute).

• Always below VMO/MMO and above VLS:4A330 aircraft, at 41000 feet, initial speed is M 0.82 (243 knots)

The maximum weight is 177 tons.4The Final Speed is 228 knots

(Buffet Speed is 212 knots at 42000 feet)

RA climb orders can be followed.

Airbus does not recommend selecting TA mode,when the aircraft is at its maximum ceiling altitude.

Aircraft at its Maximum Ceiling Altitude …Aircraft at its Maximum Ceiling Altitude …


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Contents …

• Introduction






• Conclusion


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Future TCAS Developments

• Most vertical deviations for each aircraft (following aTCAS RA order) are often greater than 300 feet.

• Very large altitude changes often lead to conflictwith other aircraft in a busy airspace.

• Due to excessive pilot reaction, uncomfortableload factors are reached.



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Future TCAS Developments …

10 20 30 40 50 600 seconds

REAL PATH

«CLIMB, CLIMB»

0

1

«CLIMB,CLIMB»

3500

2«MONITOR

VERTICAL SPEED»

3800

3

«MONITORVERTICAL SPEED»

2000

4«CLEAR OFCONFLICT»

-700

5

IDEAL PATH

1000 feet

Background …Background …


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• In addition, some operators have reported difficulty in distinguishing the V/S needle, when it is red and in the red vertical speed sector (mainly on EIS1 screens).

Improvements are anticipated in this area to help apply a TCAS RA order.

Background …Background …


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• To facilitate QUICK RESPONSE to TCAS RA orders.

• To help AVOID OVERREACTION.

• To develop an awareness to maneuver only to the extent necessary to avoid intruder aircraft.

– Improvements are currently being reviewed and developed.– Will provide pilots with pitch attitude information.– For long range aircraft, improvement is anticipated for 2006.

Planned ImprovementsPlanned Improvements


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Contents …

• Introduction






• Conclusion


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Conclusion

4Even if the number of TCAS alerts decreases,there are still missed mid-air collisions each year.

4 Pilots must always follow TCAS RA orders.

4Some improvements are envisaged and are being developed to further assist pilots in effectively responding to TCAS warnings.


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This document and all information contained herein is the sole property of AIRBUS S.A.S. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS S.A.S. This document and its content shall not be used for any purpose other than that for which it is supplied.

The statements made herein do not constitute an offer. They are based on the mentioned assumptions and are expressed in good faith. Where the supporting grounds for these statements are not shown, AIRBUS S.A.S. will be pleased to explain the basis thereof.

AN EADS JOINT COMPANYWITH BAE SYSTEMS

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