What happened
On July 7, 1968, at approximately 12:53 local time, a Mooney M-20 E, registration HB-DET, was performing a private VFR flight from Speck-Fehraltorf to Birrfeld. The aircraft was carrying the pilot and two passengers.
During the takeoff roll on the grass runway, the aircraft traveled approximately 350 meters before encountering a small undulation in the terrain perpendicular to the runway axis. In an attempt to prevent the aircraft from touching the ground again, the pilot maintained back elevator pressure. This action caused the aircraft to exceed a critical angle of attack, leading to a sudden left bank at an altitude of only 1 to 1.5 meters. The pilot was unable to recover the attitude, and the wing struck the ground. The aircraft subsequently impacted the ground heavily on its main landing gear, performed a partial roll, and came to rest in a field approximately 480 meters from the start of the runway.
The investigation
The investigation examined the aircraft's condition, the pilot's experience, and the environmental factors at the time of the accident. The aircraft, a four-seat low-wing design, was found to be in an airworthy condition prior to the event. The investigation also reviewed the takeoff performance data provided in the flight manual. While the aircraft's takeoff roll was within the theoretical limits for a hard, level runway, the investigators noted that the use of an uneven grass runway significantly altered the required performance.
Findings
- The aircraft encountered a terrain undulation during the takeoff roll.
- The pilot attempted to maintain altitude by applying elevator back pressure before the aircraft had reached a safe flying speed.
- This maneuver caused the aircraft to reach a critical angle of attack, resulting in a loss of control.
- The use of an uneven grass runway, as opposed to a smooth hard surface, contributed to the deviation from standard takeoff performance.