Accident Boeing 767-322ER N653UA, Friday 9 January 1998
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Date:Friday 9 January 1998
Time:05:00 LT
Type:Silhouette image of generic B763 model; specific model in this crash may look slightly different    
Boeing 767-322ER
Owner/operator:United Airlines
Registration: N653UA
MSN: 25391/460
Year of manufacture:1992
Fatalities:Fatalities: 0 / Occupants: 92
Other fatalities:0
Aircraft damage: Unknown
Category:Accident
Location:London-Heathrow Airport (LHR/EGLL) -   United Kingdom
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Zürich-Kloten Airport (ZRH/LSZH)
Destination airport:ZRH
Investigating agency: AAIB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
Whilst in cruising flight near Paris during an ETOPS flight from Zurich to Washington, DC, abnormal warnings appeared on the flight deck instrumentation and circuit breakers began tripping.
The commander, in consultation with the operator's maintenance control centre at London-Heathrow Airport, decided to divert and land at Heathrow. The aircraft subsequently landed safely, but during the landing ground roll the right thrust reverser failed to deploy fully and smoke appeared at the forward end of the passenger cabin. As a result, the commander ordered an evacuation when the aircraft was on the taxiway, adjacent to the landing runway. During the evacuation, the right off-wing escape slide failed to deploy and several minor injuries occurred.
A confusion in communication between the aircraft and various Air Traffic Control units resulted in the Heathrow Airport Tower controller being unaware that the aircraft was landing with technical problems until the evacuation was announced, whereupon the emergency services were alerted.

The investigation identified the following causal factors:
1. The tripping of multiple circuit breakers had been caused by the occurrence of electrical arcing and associated thermal damage to a wiring loom adjacent to the aft/upper inboard corner of the forward galley chiller unit within the Electronic and Equipment (E&E) bay, with resultant thermal damage to an adjacent loom and smoke generation.
2. Prior damage to the wiring loom insulation adjacent the aft/upper corner of the chiller unit had occurred due to contact with such units during associated removal and installation; this chiller unit had been replaced on the day before the accident.
3. Aluminium alloy swarf was present within the E&E bay prior to the accident and had probably assisted the onset of arcing between adjacent damaged wires in the loom.
4. Incorrect installation of the chiller unit, with its heat exchanger exhaust fitted with a blanking plate, would have caused warm exhaust air to discharge from an alternative upper vent which was capable of blowing any aluminium swarf around the wiring looms.
5. The crew were unaware of the potentially serious arcing fire in the E&E bay during the flight due to failure of the bay smoke warning system to activate on the flight deck, because the density of smoke emitted by the arcing wiring in the bay was not apparently sufficient to be detected by the only smoke sensor, which was located in the card and rack cooling system exhaust duct.
6. The jamming of a severely worn latch, associated with the right off-wing slide compartment, prevented that escape slide from operating during the evacuation; such latches exhibited vibration induced wear on other aircraft.

Accident investigation:
cover
  
Investigating agency: AAIB
Report number: DCA98RA016
Status: Investigation completed
Duration:
Download report: Final report

Sources:

AAIB
https://www.gov.uk/aaib-reports/5-2000-boeing-767-322er-n653ua-9-january-1998

History of this aircraft

Other occurrences involving this aircraft

17 June 2006 N653UA United Airlines 0 Washington-Dulles International Airport, DC (IAD/KIAD) sub

Revision history:

Date/timeContributorUpdates
25-Mar-2023 11:53 ASN Update Bot Added

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