09 Jan 98    (A Workup for Swissair 111?)

The captain of an airliner that flew over London despite having serious electrical problems which could have caused a fire, will be criticised this week by the government air safety watchdog.

The Air Accidents Investigation Branch describes how the pilot was forced to order an emergency  evacuation because of smoke and the risk of fire seconds after making an unscheduled landing at Heathrow.

Its report says that the captain, who had already decided it was too dangerous to continue on his scheduled route across the Atlantic, should have reported an emergency on board his aircraft before touching down in London.

That would have allowed air traffic controllers to divert the United Airlines Boeing 767-300 to Stansted and away from the heavily populated capital.

The report also points out that the captain’s failure to raise the alarm meant there were no fire tenders or other emergency services on hand when the aircraft landed at Heathrow, placing passengers at further risk.  The AAIB, which will publish its findings on Thursday, blames the incident on an electrical fault known as “arc-tracking”.

It also lists other incidents caused by the same problem, including one in which an RAF Nimrod crashed into the Moray Firth and another in which a fire broke out in the first class section of a Virgin 747 jumbo flying over Halifax, Nova Scotia.  On that occasion the blaze “self-extinguished”.

The electrical problems on the United Airlines aircraft occurred on a flight from Zurich to Washington on January 9th 1998.

The fault was discovered at 2.35pm, as the plane passed over Paris, when the crew began to experience problems with their flight instruments.

The captain, who is described as a 47-year-old male, but not named in the report, decided that it was too dangerous to fly over the Atlantic and opted instead for a London diversion.

Instead of reporting an emergency, however, he simply reported experiencing technical faults, a decision strongly criticised in the report.

It says that in future pilots must consider electrical system failures as a fire hazard and declare an emergency so that their aircraft can be diverted.

Ed Block, vice-Chairman of the International Aviation Safety Assn, a member of the United States Federal Aviation Administration’s aircraft wiring committee, and an expert on “arc-tracking”, said that there had been a serious risk of the United Airlines jet crashing.  “If that plane was in mid-Atlantic it was gone.  I think it was divine providence it didn’t come down in London”, he said.

Arc-tracking occurs when the insulation of a type of wiring known as Kapton breaks down because of age or damage.  This creates a very high temperature short circuit that ignites and destroys anything around it.

More than 60 wires were destroyed in the United incident, though to have been caused when engineers fitting a refrigerator in Washington the previous day damaged the insulation.

Numerous fatalities have been attributed to arc-tracking electrical fires.  In 1981, a Lockheed TriStar returned to Riyadh airport in Saudi Arabia after the pilot reported a fire on board.  The aircraft landed safely, but more than 300 passengers died.  A Kapton fire is suspected.

A crash off the Canadian coast involving a Swissair MD11, which killed all 229 on board, has also been blamed on arc-tracking that slowly deprived the plane of its power, radio, and controls.

The crash of a TWA Boeing 747, which blew up after take-off from New York, has also been attributed to a wiring short, which caused an explosion in the aircraft’s fuel tank.

The majority of the world’s passenger fleet contains Kapton wiring, including all Airbuses, most Boeings built before 1993, and the BAe 146, three of which are used to fly the Royal family and the Prime Minister.

A spokesman for United Airlines said the company was unable to comment until it had received and studied the air investigators’ report.



Recent Repairs, Wire Arcing Eyed in 767 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 over-water 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



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

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