What happened
On May 21, 2016, an Eurocopter AS350 B3, registration I-CMSZ, was performing a short VFR operational transfer from Arabba to Castelrotto, Italy. The flight was part of a series of aerial filming activities for the Giro d'Italia.
As the pilot approached the designated landing zone, the flight path required clearing a hill and an electrical power line, which forced the aircraft to maintain a minimum altitude of approximately 50 feet above the landing site. During the final approach, the aircraft's forward speed decreased rapidly, leading to a sudden and significant increase in the rate of descent. Despite the pilot's attempts to increase collective pitch to arrest the descent, the helicopter struck the ground with high vertical velocity. The crew, consisting of a pilot and a flight technician, escaped the impact without injuries.
The investigation
The ANSV investigation examined the aircraft's technical records, engine data from the VEMD, and video footage of the accident. The investigation also included interviews with the crew and ground personnel. Technical analysis by Airbus Helicopters confirmed that the airframe was repairable, though the impact caused the tail boom to separate and damaged the landing gear and engine mounts.
Investigators analyzed an amateur video of the event, which showed the aircraft's shadow on the ground. The footage revealed a rapid deceleration of the aircraft's translational velocity, followed by a violent impact. Meteorological data and witness statements confirmed favorable visibility and light winds, though a slight tailwind component was present during the final approach.
Findings
- The primary cause of the accident was the generation of the vortex ring state, triggered by the pilot's approach profile which involved a rapid reduction in forward speed and a steep descent.
- The pilot's chosen approach path, necessitated by local obstacles like hills and power lines, created the specific aerodynamic conditions (low airspeed and high descent rate) conducive to the vortex ring state.
- The presence of tall trees near the landing site prevented the pilot from executing a timely go-around.
- Contributing factors included the pilot's limited experience on this specific aircraft type (fewer than 100 hours) and a potential reduction in situational awareness due to the perceived simplicity of the flight task (complacency).
- A tailwind component during the final approach further contributed to the loss of effective translational lift.