What happened
On July 9, 2020, a PZL-Bielsko SZD-59 ACRO glider, registration OY-RUX, was performing a cross-country flight from Vesthimmerland (EKVH) under Visual Flight Rules. The flight began with a normal winch launch, though the pilot noted that retracting the landing wheel felt more difficult than usual. After approximately three hours of flight, the pilot began a descent toward the airfield.
During the final approach, the pilot discovered that the aircraft battery was flat. While attempting to extend the landing wheel for landing on the grass runway, the pilot found the control handle would only move approximately 25% of its required range before jamming. Due to the critical low altitude and the presence of other aircraft and ground activity on the grass runway, the pilot decided to divert to the asphalt runway. The aircraft subsequently performed a wheel-up landing on the asphalt, resulting in substantial damage to the lower fuselage and landing wheel doors.
The investigation
The investigation focused on the mechanical failure of the landing wheel system and the electrical state of the aircraft. Technical examinations of the OY-RUX in a jig revealed that while the handle functioned normally when positioned horizontally, any slight rotation of the handle tube caused the mechanism to jam.
Inspectors found that a nut used to secure the rod end to the landing wheel handle tube was loose. Furthermore, the tab washer intended to lock this nut in place was not properly bent, allowing the tube to rotate around its longitudinal axis. Additionally, the investigation noted that the pilot had reinstalled the battery after a period of charging, assuming it was sufficient, though the battery remained discharged during the flight. The investigation also found that the pilot's ability to communicate the emergency was hindered by the dead battery and a lack of clarity regarding the battery switch labels.