What happened
On April 24, 2015, at approximately 15:00 local time, a private glider, registration HB-617, was performing a VFR takeoff at Grenchen Airport (LSZG) under aero-tow. During the initial climb, the pilot detected an unidentified noise originating from the rear section of the aircraft. In response to this sound, the pilot elected to abort the takeoff and released the tow rope at an estimated altitude of five meters.
Following the release, the pilot determined that the remaining runway length was insufficient to complete a standard landing on the paved surface. Consequently, the pilot executed a landing in a rapeseed field located just beyond the end of the runway. The aircraft entered a ground loop during the maneuver, resulting in damage to the rear fuselage, as well as the elevator and rudder.
The investigation
The investigation focused on the cause of the unusual noise and the subsequent decision-making process. The pilot suggested that the noise might have been produced by the tailwheel, which continued to rotate freely after the aircraft had departed the ground. The investigation confirmed that while the pilot was uninjured, the aircraft sustained significant structural damage to its tail section.