What happened
On 22 June 2017, a Robin DR401-140B (registration F-HVAN) was performing local flight circuits at Daix aerodrome. The flight was being conducted by two instructors accompanied by a passenger to familiarize themselves with the aircraft's diesel engine and validate new checklist procedures.
During the second takeoff and circuit, the crew observed a slight variation in engine RPM, which they attributed to atmospheric turbulence. Following a full-stop landing, the crew proceeded with a third takeoff. At approximately 400 feet during the initial climb, the engine suddenly shut down. The more experienced pilot took control and executed a forced landing in a field of high crops. During the landing, the pilot applied heavy right rudder to avoid trees, causing the aircraft to yaw violently. Because the passenger had unbuckled their seatbelt prior to the aircraft coming to a halt, they were projected through the rear window, resulting in one injury.
The investigation
The BEA examined the wreckage, the engine's FADEC (Full Authority Digital Engine Control) data, and the aircraft's electrical wiring. Investigators discovered that the engine's power supply to the two independent engine computer channels (ECU A and ECU B) had been incorrectly wired. Specifically, 5A circuit breakers had been installed in series with the power supply lines due to an error on the surge suppressor mounting plate.
Technical tests revealed that the tripping threshold of these circuit breakers was sensitive to both current intensity and ambient temperature. On the day of the accident, high outside temperatures (32°C) caused the circuit breakers to trip more readily. The investigation also found that the aircraft manufacturer had not updated its electrical wiring diagrams to reflect recent modifications made by the engine manufacturer regarding the surge suppressor plate.
Findings
- The primary cause of the engine shutdown was the loss of power to both ECU channels due to the tripping of 5A circuit breakers.
- The initial failure of ECU A occurred during the second takeoff; however, the crew did not realize the change had occurred because the erroneous wiring prevented the FADECA warning light from illuminating.
- The crew's decision to continue the flight was influenced by the lack of a cockpit indication and their belief that the RPM variation was due to turbulence.
- The severity of the passenger's injury was aggravated by the fact that the passenger had released their seatbelt before the aircraft had stopped.