National Transportation Safety Board Robert L. Swaim Robert L. Swaim Systems Engineering Systems Engineering National Resource Specialist National Resource Specialist FAA Workshop November 5, 2002
BACKGROUND TWA 800 & SW111 brought focus to electrical problems & vulnerabilities… National Transportation Safety Board
B-747 Fuel Tank Arrangement TWA 800 Explosions B-747 Fire/Explosions of 5/9/76 Dry Bay Area (3) 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 gallons Surge Tanks (2) National Transportation Safety Board
TWA800 ELECTRICAL INDICATIONS TWA800 ELECTRICAL INDICATIONS CVR background noise drop-outs before explosion Fluctuating fuel flow indicator Cabin light write-ups (co-routed bundles) Fuel quantity write-ups (co-routed bundles) National Transportation Safety Board 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) National Transportation Safety Board
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 National Transportation Safety Board
Example of improper wire repair, as found in TWA 800 fuel tank. Teflon W rap Fiberglass Lacing B raid National Transportation Safety Board
Structure from beneath floor of Structure from beneath floor of Structure from beneath floor of TWA800 had repairs over wire routes TWA800 had repairs over wire routes TWA800 had repairs over wire routes Structural metal repair National Transportation Safety Board
Drill shavings were found along Drill shavings were found along wire routes in TWA800 wreckage wire routes in TWA800 wreckage National Transportation Safety Board
Which led to NTSB Which led to NTSB (then FAA & ATSRAC) (then FAA & ATSRAC) inspections that found inspections that found contamination & drill contamination & drill shavings in other shavings in other airplanes airplanes National Transportation Safety Board Drill shavings and dirt in A300
Shavings On Top Of Wires And Coming Shavings On Top Of Wires And Coming Through Bundle (747) Through Bundle (747) National Transportation Safety Board
Problems that drill shavings can lead to: Problems that drill shavings can lead to: ( NTSB Short Circuit Test results) ( NTSB Short Circuit Test results) SHAVING IN WIRE BUNDLE •Shavings Cut through some Wire Insulation •Other Shavings were Shed by Insulation •Shavings Could Transfer Energy National Transportation Safety Board
Such short circuits have caused: •System Interuptions •Misleading Displays •Unintended Operations •In-Flight Fires 767 Wire Damage at London 767 Wire Damage at London National Transportation Safety Board January 9, 1998 January 9, 1998
…NTSB inspections also found.. …NTSB inspections also found.. Chafe between fuel gauge and galley power wires (747) Chafe between fuel gauge and galley power wires (747) National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Lack of Production Illustration configuration control Lack of Production Illustration configuration control Wires Loose in Tray (747), rather than tied into separate bundles National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Lint in Circuit Breaker Panel (A300) Lint in Circuit Breaker Panel (A300) National Transportation Safety Board
Contamination may represent two sides Contamination may represent two sides of a fire triangle of a fire triangle Ignition Fuel Oxygen National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Non-Aircraft Hardware Near Wiring Non-Aircraft Hardware Near Wiring Hardware Dinner Knife National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Damaged wires that can not be visibly inspected Damaged wires that can not be visibly inspected HOLE WORN THROUGH PROTECTION (747) National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Fluid Contamination (747) Fluid Contamination (747) National Transportation Safety Board
Hydraulic Fluid In Connector (747) Hydraulic Fluid In Connector (747) Damage To Rubber Grommet BOEING SERVICE LETTER 747-SL-20-048, DATED JANUARY 25, 1995 National Transportation Safety Board
Lavatory Fluid Stains (737) Lavatory Fluid Stains (737) Damaged Blue Lavatory Wire Fluid Sleeves Stains National Transportation Safety Board
NTSB sponsored wet-arc tests NTSB sponsored wet-arc tests Cut Wires In Bundle DRIP LECTROMEC COMPANY PHOTOGRAPH National Transportation Safety Board
Wet wires could arc without tripping Wet wires could arc without tripping circuit breakers for more than 20 circuit breakers for more than 20 minutes. minutes. National Transportation Safety Board
Evidence of a Wet-short Evidence of a Wet-short PHOTO OF POLY-X WIRES AFTER 5 MINUTES OF WET-SHORT (WIRES FROM 1970-ERA 747) National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Overheated Connector Pins (747) Overheated Connector Pins (747) National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. Degraded foam hanging from clamps (747) Degraded foam hanging from clamps (747) National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. That while most wires in a bundle might appear That while most wires in a bundle might appear to be new, some insulation materials would to be new, some insulation materials would crack and be difficult to find. crack and be difficult to find. Crack in aromatic polyimide insulation, National Transportation Safety Board
Wire insulation may degrade with atmospheric exposure 60,000 HOURS LIFE (HOURS) REL. HUMIDITY TEMPERATURE DATA FROM LECTROMECHANICAL DESIGN CO SHOWN FOR MIL-W-81381 (AROMATIC POLYIMIDE)
The rate of degradation will be different in various areas of the same airplane National Transportation Safety Board DATA BY LECTROMECHANICAL DESIGN CO. MIL-W-81381 (KAPTON) WIRE DEGRADATION
…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. National Transportation Safety Board
Principal Causes of Wire Degradation, Principal Causes of Wire Degradation, per Boeing Service Letter 747-SL-20-048, January 25, 1995 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 pneumatic duct ruptures) •Chemical contamination •Heat. National Transportation Safety Board
…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. National Transportation Safety Board
…NTSB inspections also found.. …NTSB inspections also found.. The Standard Wiring Practices Manual 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. National Transportation Safety Board
NTSB stated that the FAA inadequately responded to NTSB recommendations August 2000, TWA800 Board Meeting 1967 Debris in C/B panel 1991 Debris in Delta L-1011 1998 Debris found National Transportation Safety Board in NTSB-surveyed 747
NTSB TWA 800 Finding #23 NTSB TWA 800 Finding #23 of August 23, 2000, stated that: of 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. National Transportation Safety Board
Safety Recommendation A-00-108 Safety Recommendation A-00-108 August 2000, TWA800 Board Meeting Regardless of the scope of the ATSRAC’s eventual recommendations, address all of the issues identified in the Aging Transport Non-Structural Systems Plan... National Transportation Safety Board
Recommend
More recommend
