Introduction
On 16 April 2012, an Airbus A330-343, registration G-VSXY, operated by Virgin Atlantic Airways, was involved in an accident during an evacuation after a series of spurious cargo smoke warnings. The aircraft was operating a scheduled passenger flight from London Gatwick Airport to McCoy International Airport in Orlando, USA. On board were three flight crew, ten cabin crew, and 304 passengers, including three infants.
Incident and Evacuation
Early in the flight, the flight crew received a series of smoke warnings from the aft cargo hold. The commander decided to return to London Gatwick. The crew performed the appropriate emergency drills, including discharging the fire extinguishers into the aft cargo hold, but the smoke warnings persisted. The aircraft landed safely and came to a stop on the runway. After assessing conflicting information and with smoke warnings continuing, the commander ordered an emergency evacuation.
All passengers exited the aircraft within 90 seconds, but two passengers sustained injuries classified as serious. The aircraft itself sustained only very minor damage during the evacuation. Subsequent examination revealed that the smoke warnings were spurious; no evidence of fire, smoke, or heat damage was found in the aft cargo compartment.
Investigation Findings
The Air Accidents Investigation Branch (AAIB) conducted the investigation, with participation from the Bureau d’Enquêtes et d’Analyses (BEA) representing France as the State of Design and Manufacture, supported by Airbus and Siemens.
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 Controller Area Network (CAN) Bus fault and possible high levels of humidity in the cargo compartment due to the carriage of perishable goods, which together generated multiple spurious aft cargo compartment smoke warnings.
Contributory factors included: the thermal channel fault in 10WH was not detected by internal smoke detector temperature monitoring; and the proximity of the fire extinguisher nozzles to the smoke detectors.
The CAN Bus A wiring fault caused loss of redundancy in the smoke detection system at electrical power-up, resulting in single detection mode. The root cause of the CAN Bus A fault was not determined. Fifteen separate aft cargo smoke warnings were generated, 12 by smoke detector 10WH (likely all thermal alarms) and three optical alarms from detectors 6WH and 8WH due to fire extinguishing agent discharge.
Smoke detector 10WH and 9WH had compromised insulation resistance of their T1 thermistors due to damage to the insulating envelope, degrading electrical characteristics. The cause of the damage to the Kapton film could not be determined. Acceptance test procedures and internal temperature monitoring did not detect these faults.
Additionally, the escape slide at Door 4R did not fully inflate, rendering that exit unavailable during the evacuation. The partial inflation most likely resulted from a packing fold that caused early release of the primary restraint and non-release of the secondary restraint.
Safety Recommendations
The AAIB issued several safety recommendations addressing: passenger briefings to emphasize leaving hand baggage; improvements to visual aids for escape devices; Airbus to determine and eliminate erroneous CAN Bus faults; amendment of dispatch criteria for single CAN Bus faults; Siemens to improve fault detection of thermal channel hardware failures; Airbus to introduce a maintenance requirement for smoke detector examination following fire extinguishing system activation; and EASA to review certification requirements for fire extinguisher nozzle locations relative to smoke detectors.