What happened
On 16 April 2012, an Airbus A330-343, registration G-VSXY, was operating at London Gatwick Airport when the flight crew received repetitive and intermittent smoke warnings from the aft cargo compartment. Following an assessment of the situation, the commander decided to initiate an emergency evacuation. During the evacuation process, several passengers sustained injuries. Additionally, one of the aircraft's escape slide-rafts failed to fully inflate, rendering the R4 exit unavailable to passengers.
The investigation
AAIB investigators examined the aircraft's smoke detection system and the circumstances surrounding the cargo compartment warnings. The investigation focused on the functionality of the smoke detectors and the impact of the fire extinguishing agent discharge. Technical analysis of the smoke detectors revealed that the primary source of the warnings was a specific detector, identified as 10WH.
Engineers also investigated the failure of the R4 slide-raft. It was determined that a packing fold within the unit likely caused the primary restraint to release prematurely while the secondary restraint remained engaged, preventing full inflation. The investigation also looked into the electrical integrity of the smoke detectors, specifically examining the thermistors used for temperature monitoring.
Findings
- The intermittent cargo smoke warnings were caused by a latent fault on the T1 thermistor of smoke detector 10WH, which, when combined with a CAN Bus fault and potentially high humidity from perishable goods, created sufficient conditions for spurious alarms.
- The thermal channel fault within the detector was not identified by the aircraft's internal monitoring systems prior to the event.
- The discharge of the halon fire extinguishing agent caused secondary optical alarms and degraded the humidity sensors in other detectors due to temperature drops and chemical exposure.
- The failure of the R4 escape slide-raft was attributed to an error in the packing process.
- The investigation could not definitively determine the cause of the CAN Bus fault, though the manufacturer noted a high rate of similar issues across the global A330 fleet.