What happened
On June 23, 2021, at approximately 16:52 local time, a GROB G 103 C “TWIN III ACRO” glider departed from the Stauffenbühl glider airfield in Germany. The aircraft was performing a winch launch with two occupants on board. Following the initial launch, the pilot completed three short circuit flights before beginning the final approach to runway 20 at 17:15.
During the final approach, at an altitude of approximately 30 meters above the ground, the forward cockpit canopy opened. The pilot attempted to hold the canopy or pull it closed, but this maneuver caused the aircraft to enter a steep dive. The glider struck the ground approximately 40 meters beyond the threshold of the runway. Both the pilot and the passenger sustained fatal injuries due to polytrauma.
The investigation
The BFU investigation examined the flight data, the wreckage, and video evidence. Analysis of the aircraft's flight path showed the glider had been flying in thermal lift west of the airfield prior to the accident. Examination of the wreckage revealed significant structural damage, including a broken tailplane boom, crushed cockpit structures, and broken seat shells. The investigation also reviewed the aircraft's maintenance history and the pilot's flight experience.
Crucially, video footage recorded by the passenger on a mobile phone during the flight provided evidence regarding the aircraft's configuration. The footage showed that during the winch launch, the locking lever for the forward canopy was in the vertical position, indicating that the canopy was not locked.
Findings
- The primary cause of the accident was the unsecured forward cockpit canopy, which opened during the final approach.
- The pilot's attempt to manage the opening canopy led to a loss of control and a steep descent.
- The pre-flight inspection failed to ensure the canopy locks were correctly engaged, as required by the aircraft's flight manual and standard operating procedures.