What happened
On May 9, 1977, at approximately 16:06, an Alouette III helicopter, registration HB-XFF, was conducting organized sightseeing flights near Wilderswil, Switzerland. The operation was part of a sponsored event for a local association, with passengers being picked up from a nearby path and brought to the aircraft located in a forest clearing.
To maintain efficiency and reduce mechanical wear on the rotor brake and clutch, the pilot elected to keep the main rotor running during the boarding process. The flight crew established a procedure where a flight assistant would escort passengers and secure their seatbelts. During the final flight of the session, while the assistant was occupied securing passengers in the rear seats, two passengers in the front seats were briefly left unattended. One passenger entered the aircraft through the front left door independently. During this movement, the individual's left hand made contact with the rotating main rotor, resulting in one injury.
The investigation
The investigation examined the operational procedures and the physical dimensions of the aircraft relative to the passenger. It was confirmed that the pilot held a valid commercial license and was in good health at the time of the event. The aircraft was properly registered for commercial use.
Investigators measured the clearance of the rotor plane. The main rotor height was approximately 270 cm above the ground, 220 cm above the door step, and 190 cm above the cabin floor. Based on these measurements, it was determined that the passenger must have been standing on either the cabin floor or the door step when the contact occurred, as the individual's reach with arms extended was approximately 221 cm.
Findings
- The decision to keep the rotor running was intended to prevent unnecessary wear on the rotor brake and clutch during frequent short-duration flights.
- The safety of the passengers was believed to be maintained by the presence of the flight assistant, making the spontaneous movement of the passenger unforeseeable.
- The primary cause of the accident was the improper behavior of a passenger.