What happened
On May 1, 1966, a Beechcraft Bonanza N-35, registration F-BNTB, was preparing for a local flight from Lausanne - La Blécherette airport. The aircraft was carrying a pilot and four passengers, including two children. The weather conditions were excellent, with clear skies and light winds.
During the takeoff roll on the grass runway 19, the aircraft traveled approximately 350 meters before the right wing suddenly dipped toward the ground. The aircraft then performed a right-hand ground loop on its belly, coming to a stop at the edge of the runway. While the aircraft sustained heavy damage to the fuselage, engine mount, and propeller, all occupants evacuated the aircraft without injury.
The investigation
The investigation focused on why the aircraft's landing gear began to retract while the plane was still on the ground. Technical examination of the wreckage revealed that the electric actuator had functioned, moving the gear to a position where it was three-quarters retracted before a fuse blew.
Investigators examined the landing gear control system, which includes a safety switch designed to prevent gear movement while the aircraft is on the ground and the left strut is loaded. The investigation also considered the pilot's pre-flight checks and the possibility of an accidental manual manipulation of the gear lever during the takeoff roll.