What happened
On August 18, 2013, a Robinson R22 helicopter, registration F-GHHT, was performing a general aviation flight from Mâcon Charnay to Bourg Ceyzeriat. While flying at 2,200 ft and 80 kt, the pilot heard a "LOW RPM" alarm. In response, the pilot applied carburetor heat and observed that the visual alarms had deactivated.
During the maneuver, the aircraft experienced a right yaw. The pilot applied rudder corrections, lowered the collective pitch, and noted that the audible alarm stopped and flight controls regained effectiveness. However, the pilot observed that the engine tachometer needle was at zero while the governor switch remained in the "ON" position. Believing the engine had failed, the pilot initiated an autorotation toward the south. The flight ended with a hard landing and the aircraft tipping onto its right side, resulting in the destruction of the helicopter.
The investigation
The BEA examined the aircraft's engine and mechanical systems, finding no malfunctions capable of explaining the accident. The investigation focused on the interaction between the pilot and the helicopter's governor system. On this model, if the pilot grips the power control handle firmly, the automatic coordination between pitch and power provided by the governor is inhibited, requiring the pilot to manually coordinate these inputs.
Findings
- The pilot likely gripped the power control handle tightly due to increased workload and stress while approaching the aerodrome.
- This action involuntarily inhibited the automatic pitch/power coordination provided by the governor.
- Because the pilot was no longer aware that manual coordination was required, the rotor RPM dropped, triggering the low RPM alarm and causing yawing motions.
- The pilot misinterpreted the engine power indicator (which showed values at the bottom of the dial) as an indication of total engine failure.
- The subsequent autorotation was performed based on the mistaken belief of an engine outage, leading to a late flare and the subsequent impact.