What happened
On June 29, 2013, an Eurocopter AS350 B2, registration HB-XSO, was conducting a commercial VFR flight to transport passengers and supplies for an inauguration ceremony at Alpe Trüsp. The flight originated from Lodrino, picking up four passengers at the Personico Dam.
During the approach to the alpine site, the pilot attempted a landing near several farm buildings. To facilitate the disembarkation of passengers, the pilot performed a hover with one skid partially resting on a rock. During this maneuver, the main rotor blades struck a nearby rock formation. While the pilot initially managed to maintain stability and attempted an emergency return to Lodrino, the aircraft subsequently experienced a loss of control at low altitude over the valley floor. The helicopter crashed into a quarry approximately 900 meters south of Iragna. The impact resulted in 6 fatalities (the pilot, flight attendant, and four passengers) and the total destruction of the aircraft.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the wreckage, flight plans, and witness testimonies. The investigation established that the pilot was performing a highly complex maneuver in a confined space involving significant obstacles. Investigators found that while the pilot had recently passed proficiency checks for similar types, the specific difficulty of landing on an uneven, rocky surface while managing passenger disembarkation exceeded his demonstrated capabilities. The investigation also noted that the pilot lacked specific information regarding the exact landing area, as the intended landing zone, "Er dal Zelary," was not clearly identified in the available flight documentation found at the scene.
Findings
- The primary cause of the accident was a loss of control following a failure in the tail rotor drive and hydraulic power assistance, which occurred after the main rotor blades struck a rock.
- The pilot selected a landing area with a level of difficulty that exceeded his professional flying capabilities.
- The flight continued with damaged rotor blades, likely due to an underestimation of the mechanical impact caused by the strike.
- Systemic issues were identified regarding the planning and execution of the flight operation, which failed to adhere to the established operational principles of the air operator.