What happened
On March 29, 2006, an ATR 42-320 cargo flight, operating as FAT6932 for FARNAIR, was on final approach to Geneva Airport using the ILS 23 approach. While the aircraft was at an altitude of approximately 450 feet, the crew heard a loud popping sound followed by the activation of the Master Caution warning.
The crew immediately declared an emergency due to a fire developing within the cockpit. Despite the fire, the pilots managed to land the aircraft normally and utilized the Charlie rapid exit taxiway to vacate the runway. However, the aircraft was unable to continue taxiing as the crew reported a near-total loss of all onboard electrical systems. Airport rescue and fire services (SSA) met the aircraft on the ground and instructed the crew to shut down the engines. The fire lasted only a few seconds and did not require external firefighting intervention.
The investigation
The Swiss investigation into the serious incident examined the aircraft' and the flight data recorder (FDR) and cockpit voice recorder (CVR) to reconstruct the sequence of events. Investigators worked alongside electrical system specialists from the aircraft manufacturer to inspect the 120VU compartment. The investigation focused on the electrical harness and the physical condition of the wiring supports and cables.
Findings
The investigation established that the fire was triggered by a short-circuit resulting from several installation errors. Specifically, the following factors were identified:
- The lower terminal of a bonding cable was incorrectly installed, placing it in direct contact with the electrical wire bundle, violating the required minimum clearance of 12.5 mm.
- A tubular support for the wiring harness was deformed, which altered the guidance of the wires and compromised the necessary spacing between the structure and the cables.
- The cable ties securing the wire bundle to the tubular support were insufficiently tight.
- The diameter of the wire bundle had increased due to the addition of extra wires following previous service bulletins, further reducing the available clearance.
Safety action
Following the incident, the manufacturer conducted an investigation across the ATR 42 and ATR 72 fleets, which revealed that this specific installation error had occurred on multiple aircraft. Consequently, the European Aviation Safety Agency (EASA) issued Airworthiness Directive 2006-0283. This directive mandated that all affected ATR 42 and ATR 72 aircraft undergo inspections of the 120VU electrical harness installation by the end of 2006 to ensure compliance with approved design standards.