Introduction
On 23 May 1981 at 1030 local time, a helicopter SA 315 B Lama, registration HB-XDL, operated by Air Zermatt AG, was destroyed during an attempted autorotation landing at Raron airfield in Switzerland. The aircraft was owned by Berner Oberländer Helikopter AG.
Flight Details
The pilot, a Swiss professional helicopter pilot with 545 total flight hours, was accompanied by a mechanic and a flight assistant. The mechanic occupied the left front seat, and the flight assistant sat unrestrained on nets and ropes in the rear of the cabin. The flight had been performing transport operations prior to the accident.
Accident Sequence
During the final approach to Raron airfield, at approximately 50 meters above ground, the pilot intentionally moved the turbine power lever to idle without informing the occupants, with the intention of practicing a genuine autorotation to the ground. He then pushed the cyclic forward to increase speed, aiming to achieve optimal kinetic energy for a subsequent flare. The helicopter approached a 600-meter-long field parallel to runway 27 at 180 km/h. At the end of the field, there was a paved taxiway. The helicopter flew over the field at 10 meters above ground and then settled onto the taxiway from a low height. The main rotor struck the tail boom, causing the helicopter to rotate approximately 100° clockwise around its vertical axis. The flight assistant in the rear was ejected from the cabin and sustained minor injuries; the other occupants were uninjured. The helicopter was destroyed.
Investigation Findings
- The pilot held a valid commercial pilot license for helicopters.
- The helicopter was airworthy and certified for operations.
- Weight and balance were within limits.
- Weather conditions: high-pressure system, 1/8 cumulus with base at 2000 m, 2-3/8 cirrus, visibility >10 km, wind 090° up to 6 kt, temperature 15°C, dew point 4°C, QNH 1021 hPa, sun azimuth 99° altitude 36°.
- A witness noted the autorotation was conducted with a light tailwind, corroborated by the meteorological report.
- The flight assistant was not wearing a seatbelt.
- The flight manual for the SA 315 B Lama specifies autorotation procedures: reduce collective fully, do not push cyclic forward unless speed below 90 km/h, approach into wind at 90-110 km/h (50-60 kt), perform flare at about 20 m, then increase collective and flare for landing. The pilot's approach speed of 180 km/h was far outside the recommended range.
- The pilot had previously conducted autorotations with passengers on board and had been warned by the company management that such exercises should only be performed in the presence of experienced company pilots.
Cause
The accident was caused by the pilot's execution of an intentional autorotation with an excessively high approach speed, leading to a hard landing. A contributing factor was insufficient preparation for the landing.
Probable Cause
The pilot conducted a deliberate autorotation with too high approach speed.