| http://www.herald.ns.ca/swissair/Swissair.html
Recent Repairs, Wire Arcing Eyed in B767 ETOPS Diversion James T. McKenna/Washington British investigators are assessing whether recent maintenance and the use of polyimide-insulated wiring contributed to an inflight electrical fire on a United Airlines ETOPS 767. The U.K.'s Air Accidents Investigation Branch (AAIB) is running the investigation into the Jan. 9 incident, which led to the diversion of the Zurich-Washington flight to London. The U.S. National Transportation Safety Board is participating. The problems on United Flight 965 began shortly after takeoff from Zurich for a transatlantic flight to Washington's Dulles International Airport, when a series of apparently unrelated electrical problems began occurring, the flight crew told investigators. When the aircraft was west-northwest of Paris, the flight crew was approaching the point at which they had to decide whether to continue the extended-range, twin-engine overwater operations (ETOPS) flight over the Atlantic. ETOPS rules permit twin-engine aircraft to operate on routes 180 min. or more from the nearest emergency landing airport only if the aircraft's systems meet strict conditions. Given the electrical problems, the crew opted to abort the flight and divert to London's Heathrow International Airport. After an uneventful landing at Heathrow, flight attendants reported smoke in the first-class cabin and galley. The captain ordered an evacuation after he brought the 767 to a stop on a taxiway. There were a handful of minor injuries during the evacuation. AAIB investigators examining the aircraft found about 10 circuit breakers open in the cockpit. It is not clear whether the breakers opened in flight or on the ground. They also found a roughly 7-in.-long section in a bundle of more than 100 wires that was severely burned and melted. The bundle was in the electrical and electronics (E&E) bay of the 767-322ER, directly below the first-class galley. About three dozen wires in the bundle were damaged by heat or fire. The twisted strands in one wire were fused into a single strand of copper, indicating its exposure to sustained high temperatures. There were copper globules in the damaged area, indicating active arcing occurred there. All of the damage to the bundle occurred on the inside bend of the bundle's curve over the top and down the side of a refrigeration unit. There is no evidence that the fire or heat extended up around the circumference of the bundle to the top of the bundle. The exterior of wires on another bundle about an inch away suffered thermal damage, as did foam on the rear wall of the refrigeration unit. The unit, an 86-lb. chiller for the first-class galley, had recently undergone maintenance. Investigators are trying to determine whether mechanics may have nicked insulation on a wire in the damaged bundle in the process of maneuvering the chiller out of or into its perch in the E&E bay. Most of the wires in the damaged bundle used ETFE insulation, but all of the individual damaged wires used Kapton, a type of polyimide-film insulation. Polyimide insulation has been known to break down under ``arc tracking'' if it has been previously damaged or mishandled. In arc tracking, a short circuit arcs the polyimide insulated wire and another conductor. This chars the insulator, making it conductive and capable of sustaining the arc. Sustained arcs have been shown to propagate along the wire through continuous insulation charring, triggering arcing in other polyimide- insulated wires in a bundle. Photograph: After the United Airlines 767 flight crew diverted to Heathrow, investigators found concentrated fire and heat damage in one wire bundle in the aircraft's electronics compartment. Bill Hough photo. -AW&ST 2/9/98 |
| David et al, I received this from Jim Bergquist this morning. I knew about it but not all of the details. It's a good thing that the captain made the decision to make an emergency landing when he did, or we might have had another 111 crash over the ocean. The cardinal rule was broken: YOU DON'T MIX TYPES OF WIRES!!! How many airlines and their maintenance mechnics know about this rule?? The 767 is wired with X-LINK TEFZEL (Raychem's BMS 13-48 wire) but they mixed it with KAPTON WIRE from the chiller. It would be interesting to find out, HOW MANY AIRLINES HAVE KNOWLEDGE THAT YOU DO NOT MIX DIFFERENT TYPES OF WIRES? In looking over the video tape that Swiss TV made, when I was interviewed, I saw some wire bundles in an overhanging panel in a MD-11. They were blue wires and they were DOUBLED OVER and held in that position with white plastic ties. 111 was wired with KAPTON WIRING. KAPTON insulation is brittle and can shatter, like glass, if stressed like bending over, (180 degrees), and under VIBRATION from the airplane. Another cardinal rule was broken!!! Maximum bending of A/C wire is MAXIMUM 90 degrees. I believe the whole damn air industry must be made aware of how you handle wire. They should have to pass a FAA CERTIFICATION EXAM. Make some random interviews of mechanics and maintenance supervisors and see how knowledgable they are about handling and make wire installations. You might be very surprised and yet wire is so crucial to flying SAFE, that all personnel should know how to safely handle wire. -PATRICK PRICE 
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