Accident
Last updated: 21 December 2014
Estado:Final
Fecha:lunes 26 febrero 2007
Hora:10:00 UTC
Tipo:Silhouette image of generic B772 model; specific model in this crash may look slightly different
Boeing 777-222ER
Operador:United Air Lines
Registración: N786UA
Numéro de série: 26938/52
Año de Construcción: 1997-03-23 (9 years 11 months)
Horas Totales de la Célula:43519
Ciclos:6622
Motores: 2 Pratt & Whitney PW4090
Tripulación:Fatalidades: 0 / Ocupantes: 20
Pasajeros:Fatalidades: 0 / Ocupantes: 185
Total:Fatalidades: 0 / Ocupantes: 205
Daños en la Aeronave: Menor
Consecuencias: Repaired
Ubicación:London-Heathrow Airport (LHR) (   Reino Unido)
Fase: En Espera (STD)
Naturaleza:Vuelo Internacional Programado
Aeropuerto de Salida:London-Heathrow Airport (LHR/EGLL), Reino Unido
Aeropuerto de Llegada:?
Descripción:
The accident occurred during engine start after pushback from the stand. After the right generator came online an electrical failure occurred in the right main bus. The failure resulted in severe internal arcing and short circuits inside the two main power contactors of the right main bus. The heat generated during the failure resulted in the contactor casings becoming compromised, causing molten metal droplets to fall down onto the insulation blankets below. The insulation blankets ignited and a fire spread underneath a floor panel to the opposite electrical panel (P205), causing heat and fire damage to structure, cooling ducts and wiring. The flight crew responded to the bus failure and a burning smell by shutting down the right engine and taxiing to a nearby stand. The Airfield Fire Service attended the aircraft when it arrived on stand and entered the Main Equipment Centre where they discovered significant smoke but no fire. The passengers were evacuated uneventfully via steps.

CAUSAL FACTORS:
1. An internal failure of the Right Generator Circuit Breaker or Right Bus Tie Breaker contactor on the P200 power panel inside the Main Equipment Centre resulted in severe internal arcing and short-circuits which melted the contactor casings. The root cause of contactor failure could not be determined.
2. The open base of the P200 power panel allowed molten metal droplets from the failed contactors to drop down onto the insulation blankets and ignite them.
3. The aircraft’s electrical protection system was not designed to detect and rapidly remove power from a contactor suffering from severe internal arcing and short-circuits.
4. The contactors had internal design features that probably contributed to the uncontained failures.

Fuentes:

Official accident investigation report
investigating agency: Air Accidents Investigation Branch (AAIB) - United Kingdom
report status: Final
report number: AAIB AAR 2/2009
report released:16-FEB-2009
duration of investigation:721 days (1 year 11.9 months)
download report: Report on the accident to Boeing 777-222, registration N786UA at London Heathrow Airport on 26 February 2007 (AAIB AAR 2/2009)
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