What happened
On August 8, 1975, a pilot was conducting a supervised training flight in a single-seat ASK 14 motor glider, registration HB-2001, at Grenchen Airport. The flight was intended to be a routine training maneuver. During the approach to the grass runway, the pilot shut down the engine and maintained a nose-heavy trim setting.
As the aircraft crossed the airport road on short final, the propeller moved into a vertical position. Believing the propeller needed to be horizontal for landing, the pilot attempted to manually rotate the propeller using the starter trigger with his right hand while holding the control stick with his left. During this maneuver, the pilot released the control stick prematurely before his right hand had returned to the stick. This caused the nose-heavy aircraft to pitch forward abruptly, resulting in a hard impact with the ground at a 20 to 25-degree longitudinal pitch.
The investigation
Investigators examined the aircraft and the pilot's flight history. The ASK 14 was found to be airworthy, with its weight and center of gravity within permissible limits at the time of the accident. The investigation focused on the pilot's actions during the final moments of the flight and the aircraft's trim configuration.
Technical analysis revealed that the propeller pitch remained in the takeoff position rather than being moved to the gliding position after the engine was shut down, which contributed to the propeller's rotation. Furthermore, the impact caused the central wheel's mounting to break, forcing the wheel upward against the pilot's seat. Because the pilot was secured by shoulder harnesses, this upward movement of the seat resulted in severe spinal injuries.
Findings
- The pilot maintained a nose-heavy trim throughout the flight, which contributed to the aircraft's instability when the control stick was released.
- The pilot failed to switch the propeller to the gliding position after engine shutdown, causing the propeller to move out of the horizontal plane.
- The decision to manipulate the starter trigger to reposition the propeller at such a low altitude was improper and unnecessary, as the landing gear was extended.
- The primary cause of the accident was the loss of control resulting from improper handling of the flight controls and an incorrect trim configuration.