What happened
On 21 December 2009, a DHC-8-402 Dash 8, registration G-JEDI, was performing a scheduled passenger flight from London Gatwick Airport to Düsseldorf. During the initial climb through 5,900 ft, the flight crew observed a drop in standby hydraulic system pressure, followed by multiple warnings on the aircraft's caution and warning panel. The loss of the AC electrical system was accompanied by several simultaneous indications, including the failure of both AC buses and both generators.
As the aircraft climbed toward FL120, the pilots requested a descent to avoid icing conditions. During this maneuver, the crew declared a "PAN PAN" urgency message and requested a diversion back to Gatwick. While the aircraft was able to maintain flight, the electrical failures were significant. Upon landing at Gatwick, the aircraft was found to have sustained damage to the left centre-wing section, specifically involving a wiring loom.
The investigation
Investigators examined the aircraft' and found that the failure originated in a wiring loom located in the trailing edge of the left centre-wing. The investigation focused on the physical condition of the wiring and the components of the support bracket. Engineers discovered that the wiring loom had suffered extensive fire and overheat damage, with evidence of arcing between the wires and between the wiring and the aircraft structure.
Further analysis of the wiring revealed localized mechanical damage, including abrasions containing particles of cadmium and iron. The investigation also involved testing the removed AC generators and Generator Control Units, which were found to be serviceable, suggesting the issue was not a mechanical failure of the generators themselves but rather a result of the electrical shorting caused by the damaged wiring.