Incident Overview
On 17 August 2005 at 15:17 UTC (17:17 local time), a Eurocopter BK 117 C1 helicopter, registration D-HDSR, was involved in an accident at Gombio (RE), Italy. The aircraft was operated by Helitalia SpA and was on a helicopter emergency medical service (HEMS) flight. The flight departed Parma at 15:04 UTC for a medical intervention at Gombio. Around 15:15 UTC, the pilot located the intervention site and began a reconnaissance to identify a suitable landing area, as per ENAC circular OPS-18.
Sequence of Events
As the pilot initiated the landing maneuver while in a hover approximately 1–2 meters above ground, he noticed an approaching ambulance too close to the rotor. For safety reasons, the pilot decided to move the helicopter backward. During this backward movement, the helicopter experienced a violent right yaw. The pilot, finding the anti-torque pedals ineffective, performed an immediate landing, completing a 180-degree clockwise rotation about the yaw axis. After touchdown, the pilot shut down the engines, cut off the fuel pumps, and disconnected the battery.
Aircraft and Personnel
The helicopter was a twin-engine, single-rotor aircraft of German-Japanese design, built in 2004 and registered in Germany on 8 February 2005. It had accumulated 422 hours 5 minutes of total airframe time. The aircraft was powered by two Turbomeca Arriel 1E2 turboshaft engines. The pilot, a 55-year-old Italian male, held a valid ATPL(H) license with type ratings for the BK 117 and instrument rating. He had 7,240 hours 42 minutes total flight time, including 212 hours 12 minutes on the BK 117.
Damage and Injuries
The tail rotor blades were damaged, the landing gear cross-tubes were deformed, the vertical fin was fractured, the Thomas joint between the tail gearbox input pinion and the driveshaft inside the vertical fin was broken, the support bracket for the tail rotor pitch control bellcrank was fractured, and the tail rotor servo actuator rod was damaged. The four occupants (pilot, copilot, and two passengers) were uninjured.
Investigation Findings
Post-accident examination determined that the sudden right yaw was caused by the tail rotor blades impacting tree branches, resulting in damage to the tail rotor and vertical fin and loss of aircraft control. The landing gear impact with the ground caused plastic deformation of the cross-tubes, which dissipated kinetic energy and reduced structural loads; no damage was found at the attachment points. No evidence raised concerns about the aircraft's airworthiness, and technical factors were excluded as a cause or contributing factor.
Probable Cause
The investigation identified the cause of the accident as the pilot's loss of control due to tail rotor damage resulting from a strike against a tree. Contributing to the accident was the pilot's decision to move the helicopter backward in a hover without ensuring the absence of obstacles.