What happened
On June 15, 2002, at approximately 14:45 local time, a Robin DR400-180R, registration HB-EUW, was performing a private glider tow operation in the Gantrisch region of Switzerland. The aircraft was towing a single-seat glider near the Morgetegrat ridge when the glider pilot initiated a release at an altitude of approximately 2,300 meters. Although the glider pilot radioed the release to the tow pilot, the tow pilot did not acknowledge the transmission.
Following the release, the Robin DR400-180R continued its climb briefly before entering a series of erratic maneuvers. Eyewitnesses described the aircraft performing extreme acrobatics, including steep spirals and alternating climbs and descents with high engine power and high RPM. The aircraft eventually struck the mountain slope at a nearly right angle with high velocity and a significant bank angle. The impact resulted in the total destruction of the aircraft and the fatal injury of the pilot.
The investigation
Investigators from the Swiss Transportation Safety Investigation Board (SUST) examined the wreckage and the flight dynamics of the accident. Technical analysis of the debris showed no evidence of pre-existing mechanical failures. Notably, the propeller showed evidence of high engine power at impact, with rock particles embedded in the blade surface and a broken crankshaft. The engine tachometer indicated a reading of 3050 RPM, exceeding the maximum allowable limit of 2700 RPM.
The investigation also noted that the tow cable remained fully extended and had not been retracted, suggesting the pilot did not operate the winch switch following the glider's release. To understand the aircraft's behavior, investigators conducted comparative flight tests. By releasing the control stick in a similar flight pattern, they replicated the erratic, uncontrolled flight path observed during the accident, confirming that the aircraft's movements were consistent with a lack of pilot input.
Findings
- The primary cause of the accident was a collision with terrain because the aircraft was likely no longer being piloted following the glider release.
- The pilot's engine settings remained unchanged after the release, as evidenced by the high engine RPM and power at impact.
- While an autopsy revealed significant coronary artery narrowing that could cause sudden loss of consciousness, medical evidence could not definitively prove that a medical event caused the loss of control during the flight.