What happened
On August 26, 2015, an AW139 helicopter, registration I-COLK, was conducting a Helicopter Emergency Medical Service (HEMS) mission near Sassofortino, Italy. The aircraft, operated by INAER, was responding to a primary medical emergency. Due to the inability to land directly at the scene, the crew attempted a hoist operation to deploy a doctor and a nurse onto a grassy area.
While the crew was hovering at approximately 150 feet AGL, the winch cable made contact with medium-voltage power lines. The resulting short circuit caused both the electrical line and the winch cable to break. The sudden failure caused the two medical personnel to fall approximately 7 to 8 meters to the ground, resulting in two serious injuries. The crew was unable to land immediately due to the hazard but managed to deploy a rescue technician to assist the injured personnel.
The investigation
The ANSV investigation examined the flight sequence, the condition of the aircraft, and the visibility of the obstacles. The investigation found that the crew had performed reconnaissance maneuvers, including 360-degree turns and a low-speed approach. The aircraft was found to be well-maintained, and the crew members were fully qualified and medically fit for the mission.
Investigators analyzed the wreckage and found that the copper electrical cable had failed due to melting from the short circuit, while the steel winch cable failed due to material weakening from high temperatures and subsequent overload. Crucially, the investigation determined that the power lines lacked any visual markers or warning signs, making them nearly impossible to identify from the air during the approach or the hovering phase.
Findings
- The primary cause of the accident was the crew's failure to visually acquire the power lines during the reconnaissance, approach, and hoisting phases.
- The visibility of the power lines was extremely poor from the air.
- The power lines were not equipped with any visual signaling or markers.
- There was a lack of available aeronautical information or digital mapping regarding obstacles at the specific altitudes used for this type of mission.