What happened
On June 11, 2004, an Eurocopter BK 117 B2C, registration I-HVEN, was performing a Helicopter Emergency Medical Service (HEMS) mission near San Cassiano di Val Parola, Bolzano. The flight was dispatched from Bressanone to transport medical personnel to the site of a road accident on the SP 24 provincial road.
Upon arrival, the pilot conducted an aerial reconnaissance of the area. Initially, the pilot intended to land on a dirt landing pad adjacent to the road. However, due to dust being kicked up by the rotor wash, the pilot opted to land on the paved surface of the SP 24. As the aircraft descended to approximately 2 meters above the ground, the pilot observed that the patient was located off the roadway. After consulting with the crew, the pilot decided to shift the aircraft to the right to land in a nearby parking area to keep the main road clear.
During this lateral maneuver, the pilot increased the altitude slightly to clear a road sign located at the front of the landing site. While transitioning, the tail rotor struck another road sign positioned at the edge of the SP 24. The impact destroyed the tail rotor blades, triggering a violent rightward rotation characteristic of tail rotor failure. The aircraft completed two full rotations before the pilot managed to bring the helicopter to the ground. During the first rotation, a main rotor blade struck a third road sign. The aircraft experienced a heavy landing, resulting in significant damage to the tail boom, stabilizers, and rotor components.
The investigation
The ANSV investigation focused on the sequence of maneuvers and the visibility of obstacles. Investigators found that the road sign struck by the tail rotor had not been identified by the crew during the initial reconnaissance. Furthermore, the ground medical personnel present at the scene did not report the presence of the sign via radio during the landing phase. The investigation noted that identifying vertical road signs from an aerial perspective is inherently difficult.
Technical inspections confirmed that the aircraft was in a valid state of airworthiness prior to the event, and no mechanical failures were identified as contributing to the accident.
Findings
- The primary cause of the accident was the loss of control resulting from the tail rotor striking a road sign during the landing phase.
- A contributing factor was the pilot's decision to perform a lateral shift to a new landing spot at an altitude of only 2 meters without verifying the presence of new obstacles.
- The failure of the ground crew to alert the pilot to the presence of vertical signage also contributed to the event.