Flight History
On the afternoon of 4 September 1980, the pilot of a SA 315 B Lama helicopter (registration HB-XEO) was conducting a commercial scenic flight with five passengers. The flight departed from the Air Glaciers SA heliport in Lauterbrunnen, Switzerland, and proceeded over the Wengernalp and Guggigletscher toward the Sphinx, which was circled in a wide right turn.
Accident Sequence
While flying at an altitude of approximately 3380 m near the Jungfraujoch, the pilot heard a sudden bang, followed by a slight pitching motion and weak vibrations. A scraping sound led him to initially suspect that the tail rotor had contacted a transport cable. He reduced pitch to prepare for a precautionary landing on the gently sloping firn glacier ahead. During the final approach, the pilot lowered pitch completely, intending to flare and slide uphill onto the glacier.
At that time, engine power seemed normal. However, as the helicopter descended to about five meters above the snow, the pilot heard a pumping noise. When he began to increase pitch for landing, he realized the engine was no longer delivering power. The helicopter touched down hard, and the tail section was severed. After the landing, the pilot shut down the engine and closed the fuel shutoff valve.
Injuries and Damage
The pilot was uninjured. Two passengers sustained serious injuries and were monitored in the hospital until the next day; three passengers received minor injuries and were released after outpatient treatment. The helicopter was heavily damaged. Components including the lattice tail boom, tail rotor drive shaft, and tail rotor blades were separated or damaged. All three main rotor blades were severely deformed.
Findings
The engine (Turboméca Artouste III B, serial number 1572) was disassembled and found to have a missing fixing screw for one of six labyrinth ring seals on the diffuser plate. This led to consequential damage that largely destroyed the axial compressor. The aircraft had valid certifications, and the pilot held a valid professional pilot license. The helicopter's weight and balance were within limits, but the seating configuration exceeded the approved capacity: the SA 315 B Lama is certified for one pilot and four passengers, yet on this flight there were five passengers, including a seven-year-old boy sitting on an adult's lap. Weather at the accident site was good, with 1/8 Cu clouds, unlimited visibility, light wind, and a temperature of 5°C.
Cause
The official report determined the cause as a failed precautionary landing due to sudden engine power loss.