What happened
On July 4, 2012, an Eurocopter AS350B3, registration F-OHOR, was performing a series of transport flights near Cayenne, French Guiana. During the initial engine start of the day, the pilot observed a red "GOV" warning light, indicating a malfunction in the turbine's automatic fuel regulation system. This warning electronically prevents the engine from starting.
Lacking an on-site mechanic, the pilot attempted an unauthorized troubleshooting method by toggling the "AUTO/MAN" selector switch. By switching to manual and then back to automatic, the pilot was able to clear the warning and proceed with the flight. This pattern repeated during subsequent flight legs. Upon arriving at Régina, the warning light reappeared during a hover. After several unsuccessful attempts to restart the engine using the same manual override technique, the pilot eventually managed to restart the turbine and decided to proceed with the return flight to the base with three passengers.
Approximately twenty minutes into the final leg, the "GOV" warning light illuminated again while in flight, signaling a total failure of the automatic regulation. The pilot attempted to manage the fuel flow manually using the collective pitch knob. However, during the final approach, the rotor RPM dropped significantly. The pilot attempted an autorotation, but insufficient altitude prevented a successful recovery. The helicopter struck the ground, bounced, and slid into a concrete platform, causing the aircraft to overturn and sustain heavy damage.
The investigation
The BEA examined the wreckage, the Digital Engine Control Unit (DECU), the Vehicle and Engine Multifument Display (VEMD), and the Hydro-Mechanical Unit (HMU). Investigators also analyzed video footage recorded by a passenger on a mobile phone.
Technical analysis of the DECU revealed that an electronic component—a capacitor—was failing. This specific failure mode was known to be addressed by an optional Service Bulletin (SB), but the F-OHOR had not yet undergone the recommended modification. The investigation also looked into the pilot's decision-making process and the operational pressures of the mission, which involved transporting funds.
Findings
- The primary cause of the accident was the pilot's decision to continue flight operations despite a known engine regulation alarm.
- The pilot used an unauthorized troubleshooting technique (toggling the AUTO/MAN switch) that bypassed the DECU's internal self-tests, effectively masking a developing hardware failure.
- A failing capacitor in the DECU caused the automatic regulation to fail during flight, forcing the pilot into a difficult manual regulation mode.
- During the final approach, the pilot failed to adequately synchronize fuel flow adjustments with collective pitch movements, leading to a critical loss of rotor RPM.
- The mission's nature, involving the transport of funds, may have contributed to the pressure to complete the flight despite the technical malfunction.