What happened
On February 16, 2014, a Eurocopter SA 315B (registration T7-ZST) was performing a solo VFR flight for tourism when it experienced a ground resonance event during landing at the Rotor Italia Sas helipad in Masera, Italy.
As the pilot approached the landing pad, which was oriented south, he performed a 180-degree counter-clockwise rotation while hovering approximately 5 feet above the ground. During the touchdown, the pilot noted that the right skid contacted the concrete pad with a lateral shift to the left, rather than a smooth contact, due to a crosswind component from the west/northwest.
Immediately following touchdown, intense vibrations began. The pilot attempted to reduce rotor RPM and shut off the fuel supply. However, before the engine could fully stop, one of the main rotor blades struck the tail boom. The pilot applied the rotor brake to stop the blades as quickly as possible to prevent further damage to the cockpit.
The investigation
The ANSV conducted a desk investigation, primarily utilizing the testimony of the pilot, who was the sole occupant of the aircraft. The investigation examined the aircraft's damage, meteorological reports, and the sequence of the landing maneuver.
Investigators reviewed METAR data from Milan Malpensa, which indicated moderate turbulence in the Alpine region and winds from 340°-330°. The pilot's report of a west/northwest wind was consistent with these observations. The investigation also examined the physical damage to the aircraft, including the main rotor, tail boom, landing gear dampers, and a rotor blade damper. Visual inspections of the broken components suggested that the failures were caused by sudden overloads during the incident rather than pre-existing fatigue or progressive cracks.
Findings
- The primary cause of the incident was ground resonance triggered by an improper landing technique in relation to environmental conditions.
- The pilot underestimated the impact of the lateral wind component, which led to a lateral skid or "bounce" upon touchdown.
- The environmental conditions—specifically the concrete landing surface, the partial touchdown, and the effective crosswind—created a high-risk scenario for ground resonance in this specific aircraft model.
- While the lack of a flight data recorder prevented a precise analysis of collective pitch usage, the physical evidence and pilot testimony confirm the presence of all necessary factors for the phenomenon to occur.