Accident Overview
On Thursday, 4 October 1962, at approximately 1515 MEZ, a Piper L-4 (registration HB-OGZ) departed from Lommis airfield in the canton of Thurgau, Switzerland, for a private flight. The pilot, born in 1941, held a private pilot license issued on 5 May 1960, valid until 23 December 1962, with about 70 total flying hours, of which 60 were on type. His passenger, born in 1903, was his father and had no aviation experience.
Flight and Accident
After a normal warm-up and preparation, the pilot took off from the dry grass runway, which was 525 meters long. The aircraft lifted off in the second half of the runway normally. The pilot intentionally kept the aircraft low to gain speed, but at that point engine power dropped significantly. Moving the throttle had no effect, forcing an immediate landing. The aircraft overran the airfield boundary, jumped a stream about eight meters wide and 2.5 meters deep located 150 meters west of the runway end, and came to rest on its belly in the takeoff direction. The landing gear was sheared off during the stream crossing.
Damage and Injuries
Both occupants were uninjured. The aircraft sustained serious damage. Before the investigator arrived, the wreckage was recovered and the engine was run on the ground by private parties; no discrepancies were found. The same engine subsequently flew about 20 hours without any issues.
Investigation
The investigation found no pre-existing condition to explain the power loss. The weather was fine with a temperature of 20°C and relative humidity of 60%. The runway was dry. The aircraft was a Piper Cub J-3/L-4 built in 1944, with a 65 hp Continental A-65 engine and a wooden propeller. It was owned by the Motorfluggruppe of the Thurgau section of the Aero-Club of Switzerland and had a valid permit to fly until 18 June 1963.
Discussion
The commission considered possible causes such as carburetor icing or insufficient fuel flow, but given the temperature and humidity, carburetor icing was unlikely. Other possibilities included a fuel shutoff valve not fully open or a temporary blockage of the carburetor jet by debris or water. However, no definitive evidence supported any specific cause.
Conclusion
The investigation commission concluded unanimously that the accident was caused by a sharp drop in engine power during takeoff, but the exact reason for the power loss could not be determined.