What happened
On September 16, 1987, at approximately 11:45 local time, an SA 316 B helicopter with registration HB-XPB, operated by Heli-TV S.A., was conducting commercial aerial logging operations for the municipal forestry office of Soazza in the canton of Graubünden. The incident occurred at Alp de Bec, located roughly two kilometers southwest of Soazza, where a ground crew consisting of a flight engineer, a forest engineer, and a lumberjack were present.
During the 65th rotation of the day, the pilot approached the designated drop zone with a 12-meter log suspended from a 50-meter cable. Following instructions from the flight engineer on the ground, the pilot lowered the helicopter to position the lower end of the log onto the woodpile. As the upper end of the log reached an altitude of approximately three meters, the flight engineer signaled for release, having visually confirmed that no personnel were in the immediate danger zone.
However, instead of falling parallel to the existing stack as intended, the log deviated toward a wooded slope. It struck the forest engineer, who was standing under the cover of trees writing notes with his back to the approaching aircraft, fatally injuring him at the head. The lumberjack nearby confirmed that the victim had been focused on his work and not monitoring the helicopter's final approach.
The investigation
The preliminary inquiry was conducted by Hubert Maeder and concluded in November 1988. The investigation established that the pilot was fully qualified and authorized, having completed 125 rotations with the same team the previous day without incident. The aircraft was airworthy and operating under Visual Flight Rules (VFR). Weather conditions were favorable, featuring clear skies, unlimited visibility, calm winds, and a temperature of 22°C.
The forest engineer involved had extensive professional experience with aerial logging operations and was not under the influence of alcohol. However, he was not wearing a protective helmet. The inquiry noted that while the flight engineer on the ground could only signal release once the load touched the ground to allow for final corrections, his visual assessment of the danger zone may have been compromised by the terrain or the angle of view.
Findings
The primary causal factor was the forest engineer's proximity to the drop zone during the critical phase of the operation. Despite his experience, he allowed his attention to lapse after a long series of successful rotations, assuming he was safe under the tree cover. The deviation of the log suggests that as woodpiles grow, the risk of logs rolling or shifting increases significantly.
Key contributing factors included:
- Complacency: A reduction in situational awareness due to routine operations.
- Lack of Protective Equipment: The victim was not wearing a helmet.
- Communication/Visibility: The flight engineer may have misjudged the safety of the area where the forest engineer was standing.
Safety action
The report emphasizes that aerial logging requires maximum attention from all participants. It highlights that precise placement is only possible during the early stages of stacking; as piles grow, logs are prone to rolling or deviating. The investigation concluded that all other work in the danger zone must cease during drops, and personnel must maintain strict vigilance until the hazard has passed.