jim page, 2007 chapter 7: hardware systems investigations mina handbook

Jim Page, 2007Jim Page, 2007

Chapter 7: Hardware Systems Investigations

MINA Handbook


Systems Investigation

Did the system contribute to or cause the mishap?

Jim Page, 2007Jim Page, 2007 The Systems Investigation Process

– Collect system technical data, schematics, operating and maintenance manuals.

– First review the mishap site for general conditions. Determine what systems might be involved or important. Know what systems should have been working at the time of the mishap.

– Document the “as found” condition of each system and component.– Verify

• Nomenclature• Manufacturer's part numbers• Serial number

– Tag, index and photograph all components as required.


The Systems Investigation Process

– Record the apparent functioning or malfunction of each system. Verifying that a system is ok as important as identifying failure.

– If a system is suspect, go through it subsystem by subsystem, part by part.

– Recover and identify all parts of the system. Be alert for missing components.

– Do not disassemble, if possible, until entire system is verified.

Jim Page, 2007Jim Page, 2007 Investigation Guidelines

1. Look for indicators of desired operating conditions switches on/off, value position, etc.

2. Review maintenance records for repeat write-ups or recent problems.

3. Be generally familiar with how the system works. Look for evidence of usual malfunctions. Get technical help if necessary.

4. Document as found condition and position of values, switches and other components.

5. Look for missing components.6. Verify that the system components are correct – right size, rating

and part number. Make sure that there are no extras.7. Verify compliance with service bulletins and technical orders.8. Look for what's different, color, smell, shape, location, position,

general appearance, damage. Compare to a similar system. Obvious is sometimes hardest to find.

Jim Page, 2007Jim Page, 2007 Investigation Guidelines

9. Evaluate work on connecting systems and reports from lab. 10. Review your observations, isolate important ones, positive or negative. Does anything need amplification? Several weak or inconclusive observations may provide circumstantial evidence of causation. 11. Will indications in another system reveal condition of the one you're investigation? 12. Combine observations of all systems and try to develop a pattern or trend. 13. For unrelated or contradictory evidence try introducing a time element. Try to imagine a malfunction that explains the evidence. 14. Test your observations and theory on others. Welcome criticism of your ideas. 15. Make sure your theory is solidly supported by hard evidence including testing if possible.

Jim Page, 2007Jim Page, 2007 Part Failures

– Evaluate normal operations

– Did part exceed normal parameters?• Time in service• Range of motion• Speed or capacity

– If not:• Design adequate for current operations?• Maintenance adequate for mission?• Inspections adequate for known failures?

Jim Page, 2007Jim Page, 2007 Teardown Deficiency Reports (TDR)

– Priority TDR through SPD or IM– Do not attempt disassembly– Protect the exhibit

• Custody pending shipment• Shipping instructions• Mishap event number referenced• Final disposition instructions

Jim Page, 2007Jim Page, 2007 Power Systems Investigation


– The most important step is to determine if the power system was developing power at the time of the mishap.

– This can be done by examining rotating parts and shafts. If there is severe rotational damage, it is probable that the system was producing torque at impact.


Some Key Indicators of Power on at Impact

– Torsional shaft displacement or shearing. There will be damage to shafts indicating sudden stoppage under load.

– Gear splines will be bent or fall opposite the direction of rotation. There may be symmetric scoring or rubbing on the inside of the gear casing.

– If an exhaust or hot section has at high operating temperature you would expect ductile bending rather than brittle failure under load.

– There may be massive internal damage to the engine due to sudden stoppage at impact.


– There are two categories of failure:• Failure due to breakage• Failure due to loss of power

– Failure due to breakage – conduct an overload/stress fatigue investigation

– Failure due to loss of power – trace sources of fuel, electricity, air, examine scheduling of each of the above. Examine ignition sources.


Lubricating Systems Investigation

Jim Page, 2007Jim Page, 2007 Lubricating Systems Investigation

– There are three main problems:• Too much lubricant• Too little lubricant• Contaminated or incorrect lubricant

– Discoloration, distortion and extreme wear are indicators of lack of lubricant. The worst case may be actual seizure of the moving parts.

– If bearings show a bluish color they may have been overheated from too much lubricant. In this case, the bearings churn in the lubricant instead of turning. Look for this problem in manually lubricated systems.


– In modern systems contamination of lubricants or improper lubricants are a serious problem.

– Mechanical contaminants include sand, dirt and metal bits.• Evidence will be scoring or scratching of surfaces

– Chemical contaminants include the wrong lubricant as well as other materials such as oil, fuel, hydraulic fluid, cleaners or solvents.• In some cases, the contaminant attacks the seals or tubing,

in others it may affect the metallic parts themselves.


– Carefully secure a clean sample of lubricant from the system and, if available, a sample from the supply source.

– Gather any details available about possible sources of contamination.

– Have a lab do the appropriate chemical analysis for type and amount of contamination.

Jim Page, 2007Jim Page, 2007 Investigating Bearing Failures

– The most common causes of bearing failure are lubrication-based.• Loss of lubrication results in overheated bearings and is the

most common bearing failure.• Insufficient cooling results from both too much or too little

lubricant.• Lack of lubrication can cause race skidding, identified by skid

marks on the balls or rollers.• Fatigue failure of bearing is very unusual, not usually

lubrication related, but may initiate the sequence.• Fatigue of bearing is usually the result of repeated shock or

improper installation.


Hydraulic Systems Investigation



1. Examine general condition of the system including external line, internal passages and oil plugs.

2. Review servicing and maintenance records for problems and T.O. compliance.

3. Check hydraulic pumps for condition – bench check if suspect.4. Check fluid for proper type, contamination. Look at filters.5. Check system for operation, if possible. Include all associated

subsystems, actuators, etc.6. Cap, plug or seal all disconnected lines or open components to

prevent contamination.



– CAUTION! Extremely high pressures may be present. A very small pin hole in a line can cut your hand and pressure inject toxic hydraulic fluid under your skin.

– Never investigate operating hydraulic systems without proper PPE.

– Some relief valves contain powerful springs – use proper procedures when disassembling.


Electrical Systems Investigation

Jim Page, 2007Jim Page, 2007 Electrical Systems Investigation

– The first problem is to determine if electrical power was present at the time of the mishap.

– Detailed investigation is necessary only if electrical power was not available or incorrect.

– One clue to power availability is rotational damage in generators or alternators. Major rotational damage indicates power on at the time of mishap.• Look at the commulator of an alternator for rotational scoring.

Jim Page, 2007Jim Page, 2007 Electrical Systems Investigation

– Examine transmission of power, wires, switches, circuit breakers, connectors.

– Examine generators for overload – conditions generate heat and discolor components. There may be distortion and warping of components and rotational damage. The ultimate clue is fire.

Jim Page, 2007Jim Page, 2007 Wire Failure Analysis

– Tools• Magnifying glass (10X suggested)• Multimeter

– Wires of interest• Potential ignition sources• Contributed to system failures• Mishap scenario information


Cup and Cone Fracture

• Ductile Material Tensile Loading Exceeds Tensile Strength

• Mechanical Failure


– Look for any Non-Uniform damage• Insulation damage or discoloration• Conductor melting• Beaded wire ends• Chaffing

– Documentation• Photograph before removal• Diagrams (as manufactured, as found)


Wire Failure Analysis

• When Cutting Wire for Removal

– Tag and Label Both Ends

• Unique Identification Number

• Reference in Diagrams and Photos

– Remove Largest Section Practical

• Provides Useful Undamaged Comparison Materials

• Bundles and Connectors Removed in Their Entirety End to End, if Possible


Wire Failure Analysis

• If Suspect Area is at Point of Equipment Connection

– Equipment Removed With Wire Attached

– Interconnections Demand Extreme Care in Removal

• Effective Resistance Can Be Dramatically Altered

– Corroded

– Loose

– Partially Welded Connections


• When cutting wire for removal– Tag and label both ends

» Unique identification number» Reference in diagrams and photos

– Remove largest section practical» Provides useful undamaged comparison materials

• Bundles and connectors removed In their entirely, end to end, if possible


– If suspect area is at point of equipment connection• Equipment removed with wire attached• Interconnections demand extreme care in removal

– Effective resistance can be dramatically altered» Corroded» Loose» Partially welded connections

Jim Page, 2007Jim Page, 2007 Light Bulbs & Switches Analysis

Jim Page, 2007Jim Page, 2007 Switches


Single-Pole, Single Throw Lever-Lock

Single-Pole, Double Throw Electrically Held

Guarded

TYPES OF SWITCHES

Jim Page, 2007Jim Page, 2007 Light Bulbs

Jim Page, 2007Jim Page, 2007 Significant Light Bulbs

– Warning lights – ABS, Emergency brake, etc– External lights – Headlights, tail lights, brake lights, fog

lights, etc– Interior lights – Overhead light, map light, etc– Instrument illumination – Is it set for proper illumination

level?– System status lights - Television, DVD, computer– Light circuitry similarities


On or Off?

• “On” at Impact– Stretching of Filament– Possible Globe Discoloration

• “Off” at Impact– Shattering or Brittle Filament

Fractures– Deformation without Stretching– No Deformation– Clean Bright Breaks

(Microscopic)


Light Bulb Analysis

Jim Page, 2007Jim Page, 2007 Factors Affecting Bulb Analysis

– Cold sinks at posts or filament supports– Bulb age – “Notching”– Axis of impact forces– Broken globes– Burned out bulbs – Melted globules on filament ends


Light Bulbs: Failure Characteristics

– Filament Deformation• Most important factor in investigation• Usually indicates lamp was ON at impact

– Filament Fracture• Can occur in either ON or OFF state• Brittle fracture – lamp probably OFF• Melted fracture – lamp probably ON

– Oxidation• Oxidation indicates lamp was ON

– Filament Burnout– Resonance and Entanglement

Jim Page, 2007Jim Page, 2007 Evaluation

– Document position as found– Consider impact forces/vector– Involved in fire– Proximity to other switches

• Same design, different function• Visually identified versus touch• Effect of incorrect activation


Circuit


Circuit Breaker

Jim Page, 2007Jim Page, 2007 Investigation Procedures

– When To Investigate• To determine source of ignition of a fire• To understand a system failure• To provide information about mishap scenarios

– Documentation• Record function, rating and location of breaker• Photograph and/or sketch front and rear of panel

– Removal• Mark wires and cut several inches from breaker• Loosen hardware and remove

jim page, 2007 chapter 7: hardware systems investigations mina handbook

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