What happened
On July 18, 2018, a Schempp Hirth Nimbus-4DM, registration HB-2384, was performing a self-launch at the Amlikon (LSPA) glider airfield. The flight was intended to be a cross-country flight, with the pilot and an instructor prepared for a self-launching procedure using the aircraft's retractable engine. The pilot, while experienced in flying the aircraft type, had never previously performed a self-launch in this specific model.
During the takeoff roll on runway 27, the aircraft's left wingtip initially touched the ground due to the lack of external personnel to steady the wing. As the aircraft accelerated, the instructor adjusted the flaps from position -1 to +2. Shortly after lifting off at approximately 85 km/h, the aircraft entered a sink condition and began to bank slightly to the left. The glider then struck the ground heavily on its main wheel and slid south of the runway. While the pilot escaped without injury, the instructor sustained a fractured spinal vertebra.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight data from the aircraft's flight computer, reviewed maintenance and training records, and analyzed the aircraft's flight manual. The investigation confirmed that the aircraft's weight and center of gravity were within permissible limits and that there were no pre-existing technical defects. The investigation also focused on the pilot's training history, noting that while the pilot had completed training in touring motor gliders (TMG), he had not yet completed the specific requirements for self-launching privileges in retractable-engine sailplanes.
Findings
- The primary cause of the accident was that the pilot failed to ease the elevator backpressure after takeoff to allow the aircraft to accelerate, leading to a loss of airspeed and subsequent loss of control.
- The pilot lacked prior experience in performing self-launches in retractable-engine sailplanes.
- The instructor had very limited experience flying the Schempp Hirth Nimbus-4DM.
- There was a lack of risk awareness regarding the complexities of the self-launch procedure.
- The investigation identified a systemic safety risk: using TMGs for dual instruction to qualify for self-launching privileges is insufficient preparation, as these aircraft do not share the same operational characteristics or risks as retractable-engine sailplanes.
Safety action
SUST issued a safety recommendation to the European Union Aviation Safety Agency (EASA) to ensure that training for self-launching in retractable-engine sailplanes is specifically adapted to address type-specific risks, such as sudden pitch changes during engine failure.