What happened
On April 24, 2017, a PA-22-150 aircraft, registered as HB-OPL, was conducting a technical test flight at Langenthal Airport (LSPL) in Switzerland. The flight was intended to verify the aircraft following a partial restoration completed earlier that year. The pilot and a passenger, both involved in the restoration process, prepared the aircraft for a visual flight rules (VFR) operation.
During the takeoff roll on runway 23, the aircraft lifted off after approximately 180 meters. The pilot reported that the aircraft climbed steeply and unexpectedly, coinciding with a gust of wind. In an attempt to correct the pitch and prevent the steep climb, the pilot pushed the control column forward and simultaneously adjusted the elevator trim. However, the aircraft' and the pilot's actions led to a rapid loss of airspeed, with the plane climbing at only about 30 knots up to an altitude of roughly 10 meters.
As the aircraft reached this low altitude, it entered a stall and rolled over the right wing, striking the ground. While there was no fire, the impact caused significant damage to the aircraft. Both occupants managed to exit the aircraft via the right door; the pilot was uninjured, but the passenger sustained a fractured eleventh lumbar vertebra.
The investigation
SUST investigators examined the aircraft's mechanical condition, the pilot's actions, and the cockpit configuration. The investigation confirmed that the aircraft's weight and center of gravity were within permissible limits and that the engine and flight controls were functioning correctly. There were no evidence of pre-existing technical defects that could have caused the accident.
Investigators specifically analyzed the elevator trim mechanism, which is operated by a hand crank located in the cockpit ceiling. While the pilot initially believed the trim was in a neutral position, post-accident inspection revealed the trim was actually set near the "UP" (nose-up) position. The investigation determined that the pilot had inadvertently moved the trim in the wrong direction during the critical moments of takeoff.
Findings
- The aircraft experienced a loss of control due to a stall immediately after takeoff.
- The primary cause was the pilot manipulating the elevator trim in the wrong direction, which increased the nose-up tendency and rendered the elevator controls less effective.
- The aircraft's unexpected steep climb was exacerbated by the trim being set in a position that caused an earlier-than-usual liftoff.
- Local wind gusts may have contributed to the initial instability during the climb phase.