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The Air Accidents Investigation Branch (AAIB) was notified of this occurrence by Virgin Atlantic Airways shortly after it happened and the investigation was started the same day.
The occurrence was initially classified by the AAIB as a Serious Incident. However, when it became clear that two passengers had incurred injuries defined as Serious, the occurrence was reclassified as an Accident, in accordance with ICAO Annex 13 and the United Kingdom’s ‘Civil Aviation (Investigation of Air Accidents and Incidents) Regulations 1996’. This classification as an Accident does not reflect the state of the aircraft, which sustained only very minor damage, during the evacuation.
In accordance with established international arrangements, the Bureau d’Enquêtes et d’Analyses (BEA) in France, representing the State of Design and Manufacture of the aircraft, appointed an Accredited Representative and was supported by a team which included advisors from Airbus, the aircraft manufacturer, and Siemens, systems manufacturer. The aircraft operator has co-operated with the investigation and provided expertise as required. The Civil Aviation Authority (CAA) and the European Aviation Safety Agency (EASA) have been kept informed of developments.
The aircraft was operating a flight from London Gatwick Airport to McCoy International Airport in Orlando, USA with three flight crew, 10 cabin crew and 304 passengers on board including three infants. Early in the flight the crew received a series of smoke warnings from the aft cargo hold and the commander elected to return to London Gatwick. The crew carried out the appropriate emergency drills, including the discharge of the fire extinguishers in the aft cargo hold, but the smoke warnings continued. The aircraft landed safely, the crew brought it to a halt on the runway and endeavoured to establish the extent of any fire. This produced conflicting evidence and, with smoke warnings continuing, the commander ordered an emergency evacuation.
The passengers all left the aircraft within 90 seconds but two injuries, classed as ‘Serious’, were incurred. Subsequent examination of the aircraft and its systems showed that the smoke warnings had been spurious.
The investigation identified that injuries were sustained during the evacuation of the aircraft. The evacuation was initiated based on the commander’s assessment of the available sources of information, including the repetitive and intermittent nature of the aft cargo smoke warnings.
The investigation identified the following causal factor for the intermittent cargo smoke warnings:
- A latent fault on the T1 thermistor channel of smoke detector 10WH, in combination with a CAN Bus fault and possible high levels of humidity in the cargo compartment due to the carriage of perishable goods, provided circumstances sufficient to generate multiple spurious aft cargo compartment smoke warnings.
The investigation identified the following contributory factors for the intermittent cargo smoke warnings:
The thermal channel fault in 10WH was not detected prior to the event by the internal smoke detector temperature monitoring.
The proximity of the fire extinguisher nozzles to the smoke detectors.