Robert L. Swaim Systems Group Chairman

Transcription

1 NTSB INVESTIGATION INTO TWA FLIGHT 800 AGING SYSTEMS Robert L. Swaim Systems Group Chairman LINT & DEBRIS ON L-1011 GENERATOR CABLES.

2 TWA 800 Accident The primary function of the Safety Board is to promote safety in transportation. 49CFR 800.2(a) Cause-Related Findings Why did the fuel tank explode? Safety Issue Findings WHAT HAS BEEN FOUND?

3 NTSB WIRE INSPECTIONS Total Time Since New (TTSN) B B MD B B B B B B B B B B B AIRPLANE TOTAL TIME (HOURS) Accident Airplane B TWA 800 B-747 NTSB TRANSPORT AIRPLANE WIRE SURVEY

4 HYDRAULIC B-NUT 2 INCHES OF LINT ON CABLES PLASTIC NUTPLATE WRAPPER FOIL WRAPPER IN GEN. CABLES PAPER LOOSE HOSE CLAMP CTSB / NTSB L-1011 FINDINGS OF MARCH 17, 1991

5 SHORT CIRCUIT EFFECTS : Ignition of flammable surroundings, such as lint. Destroyed or interrupted system functions. Unintended system operation. Misleading flight crew displays. INSERT PHOTO OF Lint bridging A300 crkt brkrs. Paper Lint Rivet Tails A300B4

6 WIRE EXTERNAL AGING CONTAMINATION, SUCH AS WITH DRILL SHAVINGS MECHANICAL DAMAGE USAGE FORCES THERMAL CYCLES STRESS, SUCH AS REPETITIVE FLEX AGE-RELATED LEAKAGE DUCT LEAKS HEAT TANK & NEARBY MATERIALS O-RINGS LEAK FUEL INSIDE TANKS MATERIAL DEGRADATION MAINTENANCE CONSUMPTION COLLATERAL DAMAGE AGING AIRCRAFT SYSTEM FINDINGS

7 DESIGN THE GROUP SAW PHENOMENON OF: AGE (Usage & Chemical) 3 LEGGED STOOL MAINTENANCE

8 SHAVINGS AND CONTAMINANTS

9 747 FLOOR STRUCTURE REPAIR OVER WIRE BUNDLES WITH SHAVINGS REPAIRS ABOVE WIRES WITH DRILL SHAVINGS

10 PLACEHOLDER FOR : Boeing Standard Wiring Practices manual has no directions for how to clean wire.

11 HOLE WORN THROUGH WOVEN SLEEVE AND WIRE INSULATION

12 INSERT PHOTO OF NASA 757 WORN WIRES

13 DENTS 757 CWT COMPENSATOR & WIRE ABRASIONS 747 CWT FUEL PROBE & COMPENSATOR CWT COMPENSATORS

14 INSERT CHART FROM E-4B THAT SHOWS THERMAL CYCLES

15 UNDAMAGED AREAS OF AGED POLY-X DID NOT PASS MANUFACTURER SPECIFICATIONS, BUT : WOULD BE EXPECTED TO PERFORM ADEQUATELY IN THE SHORT TERM, PROVIDED THERE IS NO ADDED STRESS BEYOND WHAT IT HAS EXPERIENCED. TESTING OF DAMAGED AREAS WITH WATER, FLUID REACHED THE CONDUCTOR IN ABOUT 1 OUT OF 5 DAMAGED AREAS. POLY-X FAILED MORE TESTS THAN OTHER TYPES (FOUND IN 1970s to AGE 7X FASTER THAN KAPTON). (SAMPLE WIRES FROM PROTECTED FUSELAGE AREAS.) RESULTS OF TESTING AGED WIRES (RAYTHEON)

16 BOEING SL 747-SL DEGRADED MATERIALS

17 Residue visible on surface - high concentrations of silver, copper, and sulfur DAMAGE BETWEEN TERM. BLOCK WIRES Compression damage to PTFE insulation where wires were in tight contact B-747 N inch ACCIDENT AIRPLANE, N93119, WING TANK Teflon Wrap Fiberglass Lacing Braid NTSB FQIS IN-TANK FINDINGS 025i h

18 B-747 N93105 PTFE insulation thinned and split through to the conductor B-747 N inch Cross-sectional view of compression damage. This Section was taken where black film can be seen on the insulation surface in Figure inch WIRE DAMAGE AND SULFIDATION

19 TIMELINE: January 1998 July 1999

20 Maintenance damage. Wear (example - Pump conduits) Parts not approved by design (example - clamps) Chafes on thin wall fuel tubes. Lightning (bonding) straps degrade & separate. Electrically isolated metal components. MISC FUEL TANK FINDINGS

21 BOEING SL 747-SL OPEN AND OVERFILLED CLAMPS

22 OVERHEATED WIRE AT PLUG

23 BOEING 747-SL CHEMICAL DAMAGE

24 STRETCHED WIRES TORN THERMAL INSULATION BLANKET THERMAL BLANKET FAILURE

25 DATA FROM LECTROMECHANICAL DESIGN CO SHOWN FOR MIL-W (KAPTON) 60,000 HOURS REL. HUMIDITY TEMPERATURE SAMPLE WIRE DEGRADATION CURVE

26 DATA BY LECTROMECHANICAL DESIGN CO. MIL-W (KAPTON) WIRE DEGRADATION

27 Boeing production illustration shows bundle separation Boeing SWPM requires 1/4 inch separation WIRE SAGS AND CHAFES

28 Results of B-767 Wire Fire, LHR, January 9, 1998 SHORT CIRCUIT REMOTE SECONDARY DAMAGE TO THRUST REVERSER INDICATION CIRCUIT CARD EXAMPLE OF HIDDEN DAMAGE FROM SHORT CIRCUIT

29 PLACEHOLDER FOR ATE