What happened
On December 1, 1977, a pilot operating a Zlin 526 L, registration HB-TRZ, departed Triengen for Speck-Fehraltorf to have the aircraft's electrical system inspected. Shortly after takeoff, the pilot noticed that the elevator was sticking. After circling the airfield to check the control functionality, the pilot decided to return to Triengen for an emergency landing.
During the final approach, the pilot attempted to check the elevator's movement by manually manipulating the control stick. While attempting to push the stick forward, the control failed to move sufficiently. This maneuver caused the aircraft to lose airspeed and bank to the left. Approximately 103 meters past the runway threshold, the left wing struck the ground. The impact caused the left landing gear to shear off, and the aircraft eventually came to a halt about 59 meters after the initial contact. The pilot survived the accident, but the aircraft was heavily damaged.
The investigation
Investigators examined the wreckage of the Zlin 526 L and discovered that the rear enclosure between the cockpit and the rear fuselage was missing. Upon dismantling the upper and lower rear fuselage skinning, investigators located a metal spring clip—a tool often used as a temporary fastener during maintenance—wedged under the elevator drive mechanism.
Forensic analysis by the Zurich City Police Scientific Service determined that the clip had likely been inside the fuselage for some time, moving between the elevator drive and the fuselage tubes. This object caused intermittent resistance when pulling the control stick, though it did not completely lock the mechanism. The investigation also noted that the landscape was covered in snow, creating a lack of visual contrast between the horizon and the sky, which complicated the pilot's perception of the aircraft's attitude.
Findings
- The primary cause of the accident was the aircraft falling below its minimum flying speed due to an excessive pitch-up maneuver near the ground.
- The interference of a foreign object (a spring clip) with the elevator controls contributed to the accident.
- The pilot was distracted and irritated by the malfunctioning elevator controls during the critical landing phase.