Robert L. Swaim - The MITRE Corporation...Robert L. Swaim Systems Engineering National Resource...

National Transportation Safety Board

Robert L. SwaimSystems Engineering

National Resource Specialist

Robert L. SwaimSystems Engineering

National Resource Specialist

FAA WorkshopNovember 5, 2002


TWA 800 & SW111 brought focus to electrical problems & vulnerabilities…

BACKGROUND


B-747 Fuel Tank Arrangement

B-747 Fire/Explosions

of 5/9/76

TWA 800 Explosions

NO. 1 & 4 Reserve 500 US gallons

NO. 1 & 4 Main 4,420 US gallons

NO. 2 & 3 Main 12,240 US gallons

Center Wing Tank 12,890 US gallonsSurge Tanks (2)

Dry Bay Area (3)


TWA800 ELECTRICAL INDICATIONSTWA800 ELECTRICAL INDICATIONSCVR background noise drop-outs before explosionFluctuating fuel flow indicatorCabin light write-ups (co-routed bundles)Fuel quantity write-ups (co-routed bundles)

Wiring continues from bundles into fuel tanks


From the TWA 800 airplane:From the TWA 800 airplane:

• Damaged Wire Insulation (Mechanical Damage & Cracks)

• Repairs & Metal Shavings Along Wire Routes

• Repetitive Maintenance Write-ups (Refueling, Cabin Lights, Galley Leaks)


From TWA 800 maintenance, NTSB found:From TWA 800 maintenance, NTSB found:

• Improper hardware and practices used for a wing tank compensator

• Open-ended Splices in Wet Areas• Concentrations of Splices• Totalizer Repair Bridged Connector Pins• Tape-wrapped Splice From Wing Tank


Teflon Wrap

Fiberglass LacingBraid

Example of improper wire repair, as found in TWA 800 fuel tank.


Structure from beneath floor of TWA800 had repairs over wire routes

Structure from beneath floor of Structure from beneath floor of TWA800 had repairs over wire routesTWA800 had repairs over wire routes

Structural metal repair


Drill shavings were found along wire routes in TWA800 wreckageDrill shavings were found along

wire routes in TWA800 wreckage


Which led to NTSB (then FAA & ATSRAC) inspections that found contamination & drill

shavings in other airplanes

Which led to NTSB (then FAA & ATSRAC) inspections that found contamination & drill

shavings in other airplanes

Drill shavings and dirt in A300


Shavings On Top Of Wires And Coming Through Bundle (747)

Shavings On Top Of Wires And Coming Through Bundle (747)


•Shavings Cut through some Wire Insulation•Other Shavings were Shed by Insulation•Shavings Could Transfer Energy

SHAVING IN WIRE BUNDLE

Problems that drill shavings can lead to:(NTSB Short Circuit Test results)

Problems that drill shavings can lead to:(NTSB Short Circuit Test results)


Such short circuits have caused:•System Interuptions

•Misleading Displays

•Unintended Operations

•In-Flight Fires

767 Wire Damage at London767 Wire Damage at LondonJanuary 9, 1998January 9, 1998


…NTSB inspections also found..Chafe between fuel gauge and galley power wires (747)…NTSB inspections also found..Chafe between fuel gauge and galley power wires (747)


…NTSB inspections also found..Lack of Production Illustration configuration control…NTSB inspections also found..

Lack of Production Illustration configuration control

Wires Loose in Tray (747), rather than tied into separate

bundles


…NTSB inspections also found..Lint in Circuit Breaker Panel (A300)

…NTSB inspections also found..Lint in Circuit Breaker Panel (A300)


Contamination may represent two sides of a fire triangle

Contamination may represent two sides of a fire triangle

Fuel Ignition

Oxygen


…NTSB inspections also found..Non-Aircraft Hardware Near Wiring

…NTSB inspections also found..Non-Aircraft Hardware Near Wiring

DinnerKnife

Hardware


…NTSB inspections also found..Damaged wires that can not be visibly inspected…NTSB inspections also found..Damaged wires that can not be visibly inspected

HOLE WORN THROUGH PROTECTION (747)


…NTSB inspections also found..Fluid Contamination (747)

…NTSB inspections also found..Fluid Contamination (747)


Hydraulic Fluid In Connector (747)Hydraulic Fluid In Connector (747)

BOEING SERVICE LETTER 747-SL-20-048,DATED JANUARY 25, 1995

DamageTo RubberGrommet


Lavatory Fluid Stains (737)Lavatory Fluid Stains (737)

DamagedWire

Sleeves

Blue Lavatory

Fluid Stains


NTSB sponsored wet-arc testsNTSB sponsored wet-arc tests

DRIP

CutWires InBundle

LECTROMEC COMPANY PHOTOGRAPH


Wet wires could arc without tripping circuit breakers for more than 20

minutes.

Wet wires could arc without tripping circuit breakers for more than 20

minutes.


PHOTO OF POLY-X WIRES AFTER 5 MINUTES OF WET-SHORT(WIRES FROM 1970-ERA 747)

Evidence of a Wet-shortEvidence of a Wet-short


…NTSB inspections also found..Overheated Connector Pins (747)

…NTSB inspections also found..Overheated Connector Pins (747)


…NTSB inspections also found..Degraded foam hanging from clamps (747)

…NTSB inspections also found..Degraded foam hanging from clamps (747)


…NTSB inspections also found..That while most wires in a bundle might appear

to be new, some insulation materials would crack and be difficult to find.

…NTSB inspections also found..That while most wires in a bundle might appear

to be new, some insulation materials would crack and be difficult to find.

Crack in aromaticpolyimide insulation,

REL. HUMIDITYTEMPERATURE

60,000 HOURS

DATA FROM LECTROMECHANICAL DESIGN COSHOWN FOR MIL-W-81381 (AROMATIC POLYIMIDE)

LIFE

(H

OU

RS

)

Wire insulation may degrade with atmospheric exposure


MIL-W-81381 (KAPTON) WIRE DEGRADATIONDATA BY LECTROMECHANICAL DESIGN CO.

The rate of degradation will be different in various areas of the same

airplane


…NTSB inspections also found..…NTSB inspections also found..

While most wires in a bundle might appear to be in new condition…

…knicks, cuts, and other mechanical damage were found in almost every airplane inspected, regardless of age.


Principal Causes of Wire Degradation,per Boeing Service Letter 747-SL-20-048, January 25, 1995Principal Causes of Wire Degradation,per Boeing Service Letter 747-SL-20-048, January 25, 1995

•Vibration•Maintenance (proper and improper)•Indirect damage (damage resulting from events

not directly related to wiring, such as pneumaticduct ruptures)

•Chemical contamination•Heat.


…NTSB inspections also found..In General

• No guidance on degradation beyond physical damage criteria

• No requirements for periodically retesting materials

• Wire insulation (Poly-X) aging problems were documented in 1975, but the material is still acceptable for use.


…NTSB inspections also found..The Standard Wiring Practices Manual…NTSB inspections also found..

The Standard Wiring Practices Manual

• Should contain acceptable materials and practices,

• FAA stated that the guidance is too general,

• Bulky and difficult to extract data.


NTSB stated that the FAA inadequately responded to NTSB recommendations

1998 Debris found in NTSB-surveyed 747

1967Debris in

C/B panel

1991 Debrisin Delta L-1011

August 2000, TWA800 Board Meeting


NTSB TWA 800 Finding #23of August 23, 2000, stated that:

NTSB TWA 800 Finding #23of August 23, 2000, stated that:

The condition of the wiring system in the accident airplane was not atypical for an airplane of its age,

and the airplane was maintained in accordance with prevailing industry practices.


Safety Recommendation A-00-108Safety Recommendation A-00-108

Regardless of the scope of the ATSRAC’seventual recommendations, address all of the issues identified in the Aging Transport Non-Structural Systems Plan...

August 2000, TWA800 Board Meeting


The FAA issues (not initiatives) in ATNSSP to be addressed were:

The FAA issues (not initiatives) in ATNSSP to be addressed were:

Physical conditions, such as…

…deterioration of wiring components……contamination……metal shavings…

…excessive dust and various fluids……cracking of…insulation in some wire types…

…ground terminal resistance……corrosion on connector pins…


…& Systemic Problems:“Current maintenance practices do not adequately address wiring components”

“…criteria is too general…details pertaining to unacceptable conditions are lacking…”

“Airlines report shortcomings in manufacturer’s maintenance and repair manual on wire”

“…Wire replacement criteria may be inadequate”

“…improper installation and repair of wiring”

The FAA issues (not initiatives) to be addressed were:

The FAA issues (not initiatives) to be addressed were:


Industry (as the ATSRAC)inspected airplanes older than 20 years,documented similar conditions, then stated that:

Industry (as the ATSRAC)inspected airplanes older than 20 years,documented similar conditions, then stated that:

“None were airworthiness concerns…”


More than 30 AD’s did result, in which the FAA stated that “safety of flight” was affected and…

Some items documented by NTSB & FAA inspections were not noted in the ATSRAC report, such as:

More than 30 AD’s did result, in which the FAA stated that “safety of flight” was affected and…

Some items documented by NTSB & FAA inspections were not noted in the ATSRAC report, such as:

Example: Chafe between fuel gauge and galley power wires (747)


ATSRAC generally inspected airplanes older than 20 years. Why inspect airplanes newer than 20 years?

ATSRAC generally inspected airplanes older than 20 years. Why inspect airplanes newer than 20 years?

Thai 737 fuel tank explosion/fire at Bangkok, March 3, 2001Photo from Reuters


While 20 years was selected as a starting point by ATSRAC, wire samples from the

<11 year-old Thai 737 exhibited:

While 20 years was selected as a starting point by ATSRAC, wire samples from the

<11 year-old Thai 737 exhibited:

Numerous sites of mechanical damage.Displaced insulation & possible wire-wire abrasion.

Cracks in aromatic polyimide insulation,

Intact portions of non-polyimides generally passed tests.


ATSRAC is developing recommendations for FAA:

ATSRAC is developing recommendations for FAA:

As an exemplar issue, the FAA ATNSSP cited “…improper installation and repair of wiring.”

The FAA established the ATSRAC, which created WG 8 to address training.

A sample syllabus was developed.

ATSRAC recommended that training be left to operators.

Currently, FAA considering what and how to implement.


The FAA EAPAS plan has six topics:The FAA EAPAS plan has six topics:

• Training• Maintenance• Design• Research and Development• Wire Reporting• Information Sharing and Outreach


Through EAPAS, the FAA does have…

Through EAPAS, the FAA does have…

Established research in issue areas,

Plans for inspection of airplanes newer than 20 years of age.

Rulemaking in progress,but no action to-date


Through incidents and sister-ships, investigations inspect a cross-section of the fleet:

As-is,In-service,Various operators,Various types,Various countries

Through incidents and sister-ships, investigations inspect a cross-section of the fleet:

As-is,In-service,Various operators,Various types,Various countries

Bashkirian TU-154M sister-ship, Freiderichshafen, Germany, July 2002


Providing NTSB with regular wire exams.Example: Aft lav harness from Dalian, China, MD-82, May 7, 2002

LABORATORIES USED INCLUDE:NTSB Materials Lab,AFRL,NASA Huntsville,Raytheon Indianapolis,Manufacturer labs,Contract labs

1. Find, recover, & identify wreckage

2. Examine at site3. Submit samples


December 2001, and10 days out of C-check:

February 2002

Over 66 months (~5½ years)

since TWA80064 months since

TWA800Photos show lint & dirt at 737 rudder pedals seen in two airplanes

since NTSB TWA800 Finding #25Photos show lint & dirt at 737 rudder pedals seen in two airplanes

since NTSB TWA800 Finding #25

The bottom line is thatno changes have been seen in recent investigations…


Nov 2000, turn-back at ATL when fire from area of wire bundle burned through skin. Evidence of lavatory fluid found in bundle and connectors.

…and final FAA action is not complete. Rulemaking will need implemention time...

…and final FAA action is not complete. Rulemaking will need implemention time...

…while in-flight problems continue.


The initiatives called for by the 1998 FAA ATNSSP plan were to be in place by October 2000 (with one exception).

Current EAPAS end-dates discussed are in 2017.

Estimated Completion:Estimated Completion:


The FAA already has regulations, AC’s, and Handbook items that

apply to cracked insulation, wear, contamination, and similar issues.

The FAA already has regulations, AC’s, and Handbook items that

apply to cracked insulation, wear, contamination, and similar issues.

The FAA can take action NOW


You don’t have to waitYou don’t have to waitMost operators already have cleanliness (motherhood) statements to refer to.

The airplanes are designed and built to standards that have an approval. Wire insulation cracks and other damage typically do not meet manufacturer or FAA approved standards that already can be cited (refer to SWPM).


THREE SUMMARY POINTSTHREE SUMMARY POINTS1. Conditions found to create previous

electrical problems continue to exist.- FAA has plans to address the issues.- FAA research has had positive results.- FAA rulemaking & implementation yet unseen.

2. Basic assumptions need to be continually revisited. - Example: Electrical systems damage exists in

airplanes of less than 20 years age.

3. Action can be taken NOW.

Robert L. Swaim - The MITRE Corporation...Robert L. Swaim Systems Engineering National Resource...

Documents

Transcript of Robert L. Swaim - The MITRE Corporation...Robert L. Swaim Systems Engineering National Resource...