What happened
On 8 July 2022, a Robin DR400-140B, registration HB-KBX, was performing a cross-country flight from Yverdon-les-Bains, Switzerland, to Lyon-Bron, France. While cruising at approximately 1,000 feet, the pilot noticed abnormal heat within the cockpit and observed the oil temperature indicator entering the red zone. Shortly thereafter, the engine ceased operation.
Unable to restart the engine, the pilot executed a forced landing in a cornfield near Culoz. During the landing sequence, the right wing struck the ground, causing the aircraft to tilt and eventually come to rest on its back. Both the pilot and the passenger escaped the wreckage without injury.
The investigation
Investigators examined the wreckage and found that the impact occurred with a shallow nose-down attitude and a right bank. The damage to the propeller, specifically one blade bent backward, supported the conclusion that the engine had shut down while in flight.
An inspection of the instrument panel revealed significant evidence of overheating and melting on the protective sleeves of the electrical wiring. This indicated that an overcurrent had occurred within the electrical system. The investigation determined that the melting of these sleeves created electrical continuity between the magneto cables and the aircraft ground, which effectively cut off the engine's ignition system.
Further examination of the electrical system revealed several unauthorized or non-standard modifications that did not comply with the manufacturer's specifications. These included:
- The addition of a cigarette lighter socket with overheating wiring.
- The use of non-standard cable types.
- The presence of redundant, unused cables.
- Failure to follow the manufacturer's established cable color-coding.
While the exact source of the overcurrent could not be identified, the investigation established that the electrical fault was the primary driver of the engine failure.