What happened
On February 4, 1974, an Alouette III helicopter, registration HB-XCB, was performing a transport mission involving personnel and supplies. After transporting two workers from Gebbo to the Avino Lake dam, the aircraft departed the dam to retrieve two additional workers. During the return flight toward Gebbo, the helicopter was cruising through the Cairasca valley near Ponte Campo di Varzo.
At approximately 14:07, the aircraft struck 15 kV high-voltage power lines. The impact caused the helicopter to plummet into the valley below, near the Cairasca torrent. The collision resulted in three fatalities and one injury. The pilot, the mechanic, and one passenger were killed, while the second passenger was ejected from the aircraft and sustained injuries.
The investigation
An official technical inquiry was launched to examine the wreckage and the circumstances of the flight. Investigators recovered various components of the wreckage, including the fuselage, the engine, and the main rotor mast, though the tail rotor was not recovered. An examination of the engine by a technical laboratory in Rome ruled out any mechanical failure or loss of power as a cause of the accident.
Witness accounts and wreckage analysis indicated that the aircraft had been flying at a lower altitude than its previous outbound leg, following a path through the valley floor. Investigators also noted that the aircraft's weight and balance were within legal limits and that weather conditions in the region were otherwise excellent.
Findings
- The primary cause of the accident was the collision with high-voltage electrical cables.
- The pilot likely suffered from sun glare, as the flight path placed the sun directly in his line of sight, significantly reducing visibility of the wires.
- The pilot's lack of familiarity with the specific obstacles in this area contributed to the accident, as he was not aware of the presence of the power lines at that altitude.
- The aircraft was flying a trajectory that followed the valley floor, which placed the cables within the flight path.