Accident
On 1 July 2013 at approximately 09:15 local time, a Eurocopter AS350 B3e helicopter, registration HB-ZMO, operated by Swiss Helicopter AG, collided with terrain in the area known as "Mändliteifi," about 430 meters southwest of Kröntenhütte, in the municipality of Erstfeld, Uri. The helicopter was destroyed by impact and subsequent fire. All four occupants—the pilot and three passengers—sustained fatal injuries.
Flight History
The pilot, a Swiss citizen born in 1980, held a commercial pilot license for helicopters with ratings for the AS350 B3 and mountain landings. He had accumulated 1443 flight hours total, with 1197 hours on the accident type. The flight was a commercial transport operation to support renovation work at the Kröntenhütte, a mountain hut of the Swiss Alpine Club.
Earlier that morning, the pilot had flown from Erstfeld with two flight helpers and a mechanic. After dropping the mechanic at Leutschachhütte and performing several rotations transporting materials at Göscheneralp and Andermatt, the helicopter refueled at Nätschen. Around 09:00, the pilot departed Andermatt overflying toward Erstfeld with the two flight helpers on board. En route, he was informed that the mechanic was ready for pickup at Leutschachhütte. He diverted there, picked up the mechanic, and proceeded toward Kröntenhütte to drop off one flight helper.
Accident Sequence
Approaching the basin south of Kröntenhütte, the helicopter crossed the Päuggenfurggi ridge at about 2450 m (8038 ft) and then the Steinchelen area with a high ground speed—the last recorded satellite navigation data indicated 135 knots (250 km/h). Several witnesses at Kröntenhütte, who had experience with helicopter operations, described the flight speed as extremely high. The helicopter was observed descending in a straight trajectory, then turning right along the terrain. It appeared to follow a descending ridge that bounds the basin to the north. Witnesses noted that the helicopter's bank angle became very steep, such that only its underside was visible. The helicopter then disappeared behind a ridge, and shortly afterward, smoke rose from behind it. No unusual sounds were reported.
Wreck and Impact
The wreckage came to rest on a ridge between Mändliteifi and Obersee, at an elevation of approximately 1950 m. Impact marks indicated a substantial forward speed and a descending flight path roughly parallel to the ridge, which slopes about 20° eastward. The crash site was located about 350 meters from Kröntenhütte, which lies at 1903 m. The helicopter caught fire immediately after impact, burning intensely.
Probable Cause
The accident was caused by collision with terrain following loss of control of the helicopter, most likely due to the occurrence of servo transparency during a right turn close to terrain. The risky flight tactic played a role in the accident.