What happened
On August 29, 1987, at approximately 10:40 local time, a student pilot was conducting a navigation exercise over the Glarus region in Switzerland. The flight involved a Hughes 269C helicopter, registration HB-XKD, operated by Fuchs Helikopter based in Schindellegi.
The aircraft had been positioned on the roof of a manufacturing hall in Schindellegi before being flown down to a designated refueling spot on the factory grounds near fuel pumps. After landing, the pilot reduced the engine power to 2000 RPM and tightened the locknut on the throttle twist grip. He then exited the aircraft to refuel the main tank.
While the student was holding the fuel nozzle in the tank opening, preparing to activate the flow, the helicopter unexpectedly lifted off the ground. It touched down again a few meters away and tipped over. The pilot, who was alone at the site, managed to escape injury after attempting to restrain the moving aircraft.
The investigation
The Swiss Transportation Safety Investigation Board (STSB/SUST) examined the operational context and mechanical state of the helicopter. The student pilot held a valid learner permit and had logged 23 hours of flight time, all in the accident model. His instructor was not present during the pre-flight preparations or the refueling process.
Technical findings confirmed that the rotor clutch engages automatically when engine speed reaches 1500–1600 RPM and remains engaged if power is reduced to 2000 RPM. Crucially, the main pitch control lever is equipped with a friction brake. In this instance, the friction brake had not been tightened before the pilot exited the aircraft.
Weather conditions were calm with no wind, a temperature of 15°C, and high pressure (1620 hPa QNH). The helicopter was airworthy and certified for flight.
Findings
The accident resulted from the student pilot leaving the helicopter in a state that did not prevent unintentional lift. Because the friction brake on the pitch control lever was loose, the lever gradually moved upward due to engine vibration and mechanical forces. This increased the angle of attack of the rotor blades until sufficient lift was generated to raise the unloaded aircraft.
The investigation noted that while the specific friction brake design on this Hughes 269C model relies on a spring-loaded hand lever which may not provide absolute security against movement, standard aviation practice requires securing the aircraft against unintended motion. The operator’s handbook stated that during engine operation, a responsible person should remain in the pilot's seat, or if exceptions are made for work flights, the rotor must be disengaged and all friction brakes secured.
Safety action
The report highlighted the critical importance of securing pitch controls and ensuring the rotor is disengaged or the aircraft is otherwise immobilized when leaving an engine-running helicopter. No further external safety recommendations were issued in this specific historical context, as the primary finding was attributed to procedural non-compliance by the pilot.