What happened
On August 11, 1966, a Piper L4-J3, registration HB-OGZ, departed from Lommis airfield for a training flight. The flight, part of a flight school course, was intended to practice simulated emergency landings. Shortly after takeoff, the instructor reduced power to initiate the maneuver, instructing the student pilot to perform an emergency landing. However, the engine failed completely during the glide.
In an attempt to restart the engine, the instructor applied significant nose-down pitch to increase airspeed. Due to the low altitude, the maneuver had to be aborted to clear trees and telephone lines. The instructor then executed a left-hand slip towards a nearby field. During the final pull-up, the aircraft, traveling at a low speed, struck a small earthen embankment formed by a field path. The impact tore away the landing gear, causing the aircraft to skid on its fuselage for approximately 20 meters before coming to a halt. There were no injuries to the instructor or the student.
The investigation
The investigation examined the engine performance, the aircraft's maintenance history, and the environmental conditions at the time of the accident. The Piper L4-J3 had undergone a 33-hour inspection just days prior and was considered airworthy. Investigators also looked into the possibility of carburetor icing, noting high humidity levels (90-95%) and the specific characteristics of the Continental A-65 engine, which is sensitive to rapid throttle reductions and low idle speeds.
Findings
- The engine failure was likely caused by a combination of factors, including a potentially lean fuel mixture due to operating temperatures, a rapid reduction in power, or carburetor icing.
- The instructor failed to notice the small embankment crossing the landing path, possibly due to the rapid sequence of events, low sun angle during sunrise, or light haze.
- The aircraft's low airspeed during the final stage of the maneuver contributed to the severity of the impact with the ground obstacle.