What happened
On August 30, 1990, at approximately 08:25 local time, an AS 350 B1 "Ecureuil" helicopter (HB-XTF), operated by Heli Gotthard AG, landed on a narrow pull-off area along the Klausen Pass in Uri. The pilot had positioned the aircraft at a slight angle to the road to ensure that the still-spinning main rotor blades would not encroach into the traffic lane. While two flight assistants disembarked from the left side to unload equipment, a local farmer approached the helicopter from the rear right side. Intending to assist with the ground operations, the farmer bent slightly to pass under the tail boom. At this location, the clearance between the ground and the tail rotor was approximately 1.4 meters due to the terrain's slope, significantly higher than the standard 65 cm found on flat ground. The farmer failed to notice the rotating tail rotor, which was difficult to see against the background, and was struck in the head by the tip of a tail rotor blade.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the circumstances surrounding the incident. The pilot held a valid license and had sufficient flight hours. The helicopter was airworthy and properly maintained. The investigation focused on the positioning of the aircraft, the visibility of the tail rotor, and the actions of the third party involved. It was determined that the pilot's decision to angle the helicopter was a reasonable compromise to keep the main rotor clear of traffic, but it resulted in the tail rotor being positioned closer to the ground than usual and partially obscured from certain angles.
Findings
The primary cause of the accident was the inattention of a third party who did not perceive the rotating tail rotor. Contributing factors included:
- The farmer's spontaneous intention to help the flight crew.
- The narrowness of the landing area and restricted overall visibility.
- The difficulty in discerning the tail rotor due to its color and motion.
- The increased ground clearance of the tail rotor (1.4 m) at the specific accident site, which made it less obvious than a lower-hanging rotor might be on flat terrain.
Safety action
The SUST recommended that measures be explored to make rotating tail rotors more visible to ground personnel and bystanders.