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.
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.
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
would have allowed air traffic controllers to divert the United Airlines
Boeing 767-300 to Stansted and away from the heavily populated capital.
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”.
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”.
electrical problems on the United Airlines aircraft occurred on a flight
from Zurich to Washington on January 9th 1998.
fault was discovered at 2.35pm, as the plane passed over Paris, when the
crew began to experience problems with their flight instruments.
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.
of reporting an emergency, however, he simply reported experiencing
technical faults, a decision strongly criticised in the report.
says that in future pilots must consider electrical system failures as a
fire hazard and declare an emergency so that their aircraft can be
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.
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.
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.
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
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.
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.
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.
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
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
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