What happened
On 15 March 2009, an Airbus A319-131, registration G-EUPZ, was preparing for a commercial flight from London Heathrow to Edinburgh. During the engine start sequence, the crew successfully started engine No 2, but as engine No 1 came online, the aircraft experienced a sudden loss of power to the primary flight display and navigation display. This was accompanied by a master caution aural warning and a visible dimming of both cockpit and cabin lights.
Following the ECAM (Electronic Centralised Aircraft Monitoring) procedures, the crew attempted to reset generator No 1. During this reset, a loud noise emanated from behind the right circuit breaker panel, followed by a noticeable smell of electrical burning. Although no smoke was visible, the crew elected to return the aircraft to the parking stand. After the aircraft was parked, the crew noted that the electrical system had experienced significant faults, including messages regarding AC bus 1 and the electrical generator.
The investigation
The AAIB investigation focused on the area behind the 123VU circuit breaker panel. Examination of the aircraft revealed extensive heat damage, including a hole melted through the aluminium structure and significant sooting. The investigation found that the AC Bus 1 busbar had suffered severe damage, with melting of copper terminals and evidence of electrical arcing.
Investigators also analyzed the presence of a specific type of dust found on the exposed busbar terminals. This dust contained metallic flakes and organic matter, and laboratory tests indicated that high chloride levels could increase its conductivity, potentially facilitating electrical tracking. While the investigation could not definitively identify the exact initiating event due to the destruction of the area by the fire, the evidence pointed toward a transient short circuit.
Findings
- The electrical fire and initial fault likely originated from a short circuit or transient arc occurring between circuit breaker 11QA and AC Bus 1.
- The fire was intense, with temperatures estimated to have exceeded 1084°C, causing significant damage to the busbar and surrounding structure.
- The presence of conductive dust on the terminals may have contributed to the propagation of the fire by reducing the creepage distance between phases.
- It is possible that a loose, conducting article entered the area and caused the initial short, though no such object was recovered as it likely vaporized during the event.
Safety action
- The implementation of updated Electrical Wiring Interconnection Systems (EWIS) requirements and enhanced maintenance and training programs is expected to reduce the risk of electrical faults caused by foreign objects and debris.