What happened
On June 27, 2015, an ASK 21 glider, registration HB-1962, was performing a flight instruction session at Bex aerodrome (LSGB). The flight was being conducted under Visual Flight Rules (VFR) via aero-tow, with a Piper PA18 acting as the tug aircraft.
Following takeoff from runway 33, the instructor began a series of maneuvers designed to demonstrate extreme towing positions to the student. The sequence involved positioning the glider below the tug to introduce turbulence, followed by moving to the right and climbing to a position slightly above the tug. During these maneuvers, the instructor noted the aircraft drifting left and corrected the position to stay slightly above and aligned with the tug's axis.
As the instructor attempted to move the glider to the left side of the tug to continue the exercise, the tow rope began to slacken. Recognizing the developing danger, the instructor initiated a release of the rope. However, the released rope struck the right wing of the glider before breaking. A portion of the rope became entangled in the partially extended airbrake on the right wing. The instructor subsequently navigated the glider toward runway 33, announcing the intention via radio, and performed an emergency landing in a field adjacent to the runway, eventually coming to a stop on the runway itself. Both occupants remained uninjured.
The investigation
The investigation focused on the mechanics of the rope release and the subsequent impact with the glider's airframe. Investigators examined the flight path, the specific maneuvers being performed at the time of the release, and the physical state of the aircraft, specifically the damage to the right wing caused by the rope impact.