Flight History
On 23 June 2008, an Agusta A109K2 helicopter, registration HB-XWJ, was conducting a landing on the helipad located on the roof of Samedan Hospital in Switzerland. During the landing sequence, the helicopter experienced ground resonance, a phenomenon where the rotor system and the landing gear oscillations couple, leading to instability. The aircraft sustained damage as a result.
Aircraft Information
The helicopter involved was an Agusta A109K2, a twin-engine light utility helicopter. According to the manufacturer's specifications, the A109K2 has a four-blade main rotor and a tail rotor. The helicopter was equipped with an autopilot system. Examination of the autopilot revealed that its technical condition was poor, and the investigation noted that this condition may have contributed to the accident.
Helipad Information
The helipad at Samedan Hospital was constructed on the hospital's roof. The investigation determined that the helipad's design was not professionally executed. Specifically, the construction did not meet proper engineering standards, which rendered it unsuitable for the landing loads of the helicopter, thereby predisposing the aircraft to ground resonance during touchdown.
Investigation Findings
The Swiss Accident Investigation Board (SAIB) conducted the investigation. The board examined the wreckage, the helipad structure, and the helicopter's components, including the landing gear and autopilot system. The landing gear showed signs consistent with ground resonance. The helipad's structural strength substantiation did not comply with established criteria.
Cause
The accident is attributable to ground resonance during landing because the helipad's construction was not professionally designed. The poor technical condition of the autopilot system may have contributed to the accident.