What happened
On Saturday, October 18, 2003, at 17:15, a private flight involving three autogyros departed from the Bois-de-la-Pierre ultralight airfield in Montégut-Bourjac, France. The pilot was leading a formation flight at an altitude of approximately 300 meters, heading southwest. During the flight, the group performed two circles over a residential area to fly over family members working at a nearby construction site.
As the pilot navigated around the construction site, witnesses observed the pilot waving with his left hand. Shortly after this gesture, observers noted parts of the aircraft's structure separating from the airframe. The W31-SP then fell vertically, with the main rotor having ceased rotation. The aircraft struck the ground at the Boulbenes site, resulting in the death of the pilot and the total destruction of the amateur-built autogyro.
The investigation
The investigation focused on the debris field and the mechanical state of the aircraft, which was powered by a 100-hp Rolls Royce engine. Investigators found fragments of the propeller distributed in a 50-meter radius and identified a severed horizontal stabilizer and a rudder separated at the hinges. The main wreckage was located 70 meters from the initial debris.
Key mechanical findings included:
- The wooden propeller blades were broken at the hub.
- The engine had become detached from the airframe.
- The main rotor blade flapping stops were found bent.
- The rotor blades showed impact marks consistent with striking the tail section and the propeller.
- The throttle mechanism lacked a feature to maintain engine RPM when released.
Findings
The accident was triggered when the pilot released the throttle to wave to bystanders. Because the throttle lacked a hold mechanism, it automatically returned to the idle position, creating a nose-down pitching moment. In an attempt to correct this, the pilot likely applied a sudden increase in power.
On this highly responsive aircraft, this surge in power caused a steep climb. The resulting flight path induced a decrease in load factor and rotor speed, leading to rotor blade flapping. The blades moved beyond the limits of the flapping stops, striking the tail assembly and the propeller. This impact caused the main rotor to stall and the engine to lose propulsion, resulting in the vertical descent and fatal impact.