What happened
On September 14, 2007, at approximately 18:30, a Magni M 22 Voyager gyrocopter, identified as 74-VA, was conducting a local pleasure flight near Lake Geneva. The aircraft, operated by a private individual, departed from a private ultralight airfield at Thollon-les-Mémises at an altitude of 3,000 feet, carrying the pilot and one passenger.
After roughly thirty minutes of flight, the pilot initiated a climb to perform a standard vertical pass over the runway, followed by a left-hand downwind leg for landing. During the base leg, an observer on the airfield noted the aircraft flying at a low altitude with a steep left bank. The aircraft subsequently disappeared behind a line of trees. During the descent, the observer noted an increase in engine RPM. The gyrocopter struck the ground in a ravine approximately 150 meters from the runway threshold, resulting in a post-impact fire. The accident resulted in one fatality (the pilot) and one serious injury (the passenger).
The investigation
The investigation focused on the aircraft's flight path and the mechanical state of the rotor system. Examination of the wreckage revealed that the tail section struck the ground first with high vertical velocity. Notably, the rotor assembly showed minimal deformation, indicating that the rotor was spinning at a low speed at the moment of impact. No mechanical anomalies prior to the accident were identified.
Investigators also analyzed local meteorological conditions. At the time of the accident, winds were recorded between 6 and 15 knots, but witnesses reported recent gusts of approximately 40 km/h. The aircraft was operating near its maximum takeoff weight and was positioned on the leeward side of the nearby terrain.
Findings
The investigation established that the primary cause of the accident was the failure to detect or adequately react to a decrease in rotor RPM. The combination of the preceding climb and the presence of downdrafts caused by the mountainous terrain likely led to a gradual reduction in rotor speed. As the pilot applied a load factor during the landing maneuver, the rotor speed reached a critical threshold, leading to an irreversible decay in RPM and subsequent blade stall. Additionally, the pilot's insufficient consideration of local meteorological conditions, specifically the risk of downdrafts in the valley, contributed to the loss of control.