Background
On 1 May 1966, a Beechcraft Bonanza N-35, registered F-BNTB, was stationed at Lausanne-La Blécherette aerodrome in Switzerland. The aircraft was owned and operated by Aéro-Club J.D. The pilot, born in 1929, held a private pilot license issued on 13 May 1958 and had a total flight experience of 276 hours 43 minutes, including 68 hours on the Bonanza N-35. The aircraft carried four passengers: two adults (born 1930 and 1926) and two children (born 1957 and 1958). The weather at the time was excellent, with 1/8 cumulus cloud cover, 8 km visibility, a variable surface wind of 5 knots, temperature 20°C, and QNH 1022 mb.
Accident Sequence
At approximately 1617 hours local time, the aircraft began its takeoff roll on grass Runway 19. The pilot reported using 12° of flaps and applying full throttle. After rolling about 350 meters, the aircraft sank onto its landing gear, the right wing struck the ground, and the aircraft executed a half-turn to the right on its belly before coming to rest at the edge of the runway. The pilot stated that he did not manipulate the landing gear controls and that the aircraft never left the ground. Two witnesses, an airfield duty officer and an air traffic controller, described a steep pitch attitude and possible stall before the right wing dropped.
Investigation Findings
Technical examination revealed that the landing gear retraction system had been activated: the electric actuator motor had run, the gear was three-quarters retracted, and the system's fuse had blown when the gear became blocked. The electrical system was later tested and found to be in working order. The pilot had not confirmed during pre-takeoff checks that the landing gear control switch was in the down and locked position. The aircraft was within weight and balance limits, and no mechanical defects were discovered. The grass runway had a slope of approximately 11 meters over the first 500 meters, which the report considered favorable for takeoff.
Probable Cause
The accident was attributed to the landing gear retracting prematurely during takeoff, the pilot having likely not ensured that the landing gear controls were in the down and locked position.
Damage and Injuries
The aircraft sustained serious damage, estimated at 20% of its value, including a partially retracted landing gear, crushed lower fuselage, twisted engine mount, and damaged propeller. All four passengers and the pilot exited the aircraft without injury.