What happened
On November 1, 1997, a Pilatus PC6 B2-H2, registration F-GHXS, departed from Laon-Chambry aerodrome to perform a series of parachute jumps. The flight was part of a routine operation following a 100-hour inspection. After several successful jumps, the aircraft took off again at 11:40 UTC carrying eight passengers.
Shortly after takeoff, witnesses observed the aircraft flying in level flight at approximately 1,000 feet. The aircraft then appeared to bank to the right and entered an increasingly steep dive. Within moments, the aircraft struck the ground nearly vertically in a marshy area about 1.5 km from the airfield. The impact was so severe that the left wing detached from the fuselage before hitting the ground. All nine fatalities (the pilot and eight passengers) were confirmed.
The investigation
The investigation focused on the aircraft's flight controls, specifically the horizontal stabilizer mechanism. Because the aircraft was not equipped with flight recorders, investigators utilized 8mm video footage from cameras worn by passengers to reconstruct the final moments of the flight.
Technical examinations were conducted on the stabilizer actuator and the control cables. The investigation also compared the handling characteristics of this specific model, which uses manual controls, with the pilot's recent experience on a similar Pilatus model equipped with electric actuators.
Findings
Investigators established that the accident was caused by a loss of pitch control resulting from the horizontal stabilizer being moved into a full-nose-down position.
Key contributing factors included:
- The pilot interrupted the flap retraction sequence after takeoff to manipulate the manual stabilizer crank.
- The pilot and a passenger focused their attention on the stabilizer handle, leading to the stabilizer being set to a position that prevented the pilot from maintaining pitch equilibrium.
- The combination of the stabilizer position, flap settings, and engine power created extreme aerodynamic forces on the control column, making recovery impossible.
- The pilot's recent training had been conducted on a PC6 B2-H4, which features electric controls, whereas the F-GHXS required manual manipulation of the stabilizer.
- The pilot was likely unaware of the specific aerodynamic phenomenon where certain manual stabilizer adjustments can lead to an aerodynamic lock, which may have been misinterpreted as a mechanical failure.