What happened
On March 28, 2005, a DG-500 ELAN Trainer glider, registration PH-939, departed from the southwest strip at Terlet for a local flight. The aircraft was occupied by a pilot, who was an instructor in training, and a student acting as a passenger. After the winch cable was released at an altitude of approximately 450 meters, the aircraft entered a period of flight within cloud cover.
Upon emerging from the clouds, the pilot initiated a left turn and increased speed to approximately 230 km/h. The pilot then executed a right-hand turn with a steep bank angle between 70 and 80 degrees, intending to complete a 180-degree turn under high G-loading, estimated at approximately 5G. During the attempt to level the wings, the pilot encountered significant control forces and was unable to reduce the bank angle to below 45 degrees. Despite various control inputs, the aircraft's responsiveness was minimal. The glider subsequently entered a series of roughly four circular paths, losing altitude continuously, before impacting forested terrain east of the A50 motorway. Both occupants sustained injuries.
The investigation
The investigation examined the aircraft's technical condition, the pilot's flight history for the day, and the environmental conditions. At the time of the accident, visibility was poor due to misty weather, making the horizon difficult to discern. The investigation noted that the pilot had performed a similar high-speed, high-G maneuver earlier that same day.
Technical examination of the PH-900 wreckage provided no evidence of mechanical failure that could explain the incident. While the pilot reported extreme control forces, the investigation could not confirm if the aircraft's structural or aerodynamic limits had been exceeded, though the aircraft was certified for aerobatic flight with a limit of +7.0G.
Findings
- The pilot's inability to recover the bank angle and the subsequent circular flight paths suggest the aircraft may have entered a spiral dive, which the pilot failed to recognize or correct using proper recovery procedures.
- The high G-loads experienced during the maneuver could have contributed to spatial disorientation, especially given the poor visibility and the difficulty in identifying the horizon.
- The maneuvers performed had no specific training objective and provided no added value to the pilot's instruction.
Safety action
- Performing high-speed, steep-bank maneuvers at low altitudes under conditions of poor visibility is unsafe and should be avoided.
- The investigation raised concerns regarding the appropriateness of exposing passengers to the inherent risks of high-G, high-speed maneuvers during training flights.