AAIB investigation to Airbus A330-323, N276AY
Emergency evacuation at parking stand after APU failure filled cabin with smoke, London Heathrow Airport, 26 June 2016.
Summary:
The cabin filled with smoke whilst the aircraft was on stand after boarding. The cabin crew were unsuccessful in making contact with the commander, and one of the flight attendants (FAs) initiated a passenger evacuation.
Several passengers exited using the emergency slides from the two aft doors, but most left using the jetbridge at exit 2L. Passengers opened the two emergency exits situated immediately aft of the wings (exit 3L and exit 3R). Exit 3L had not been armed, so the slides did not deploy and the passengers did not use the exit. Exit 3R was armed and opened by a passenger and the slide deployed, but this exit was not used either.
The commander attempted to halt the evacuation, (because he believed he had isolated the source of the smoke) which caused some confusion until the FAs encouraged all remaining passengers to exit via the jetbridge.
Air Traffic Control (ATC) observed the incident and alerted the emergency services, which reached the scene quickly. Three passengers and several FAs received treatment for the effects of smoke inhalation and one passenger suffered a minor leg injury while using an escape slide.
The source of the smoke was traced to a failure of the Auxiliary Power Unit (APU) load compressor carbon seal that allowed hot oil to enter and pyrolyse in the bleed air supply. Metallic debris in the shared oil system compromised the load compressor bearing, leading to the failure of the load compressor carbon seal.
The APU manufacturer has taken action to address this type of event, and the relevant section of the Master Minimum Equipment List (MMEL) has been reviewed and amended. Six Safety Recommendations are made in the areas of interphone design, passenger briefings and the co-ordination of pilot and cabin crew training. A further two Safety Recommendations are made concerning modification to enhance automatic APU shut-down protection in the event of lubrication system contamination.
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Safety Recommendation document: