What happened
On October 7, 2017, an Agusta AW139, registration I-TNDD, was conducting a Helicopter Emergency Medical Service (HEMS) mission near Monte Casale in the Pietramurata area of Trentino, Italy. The crew was responding to a call regarding a climber who had fallen approximately 20 meters.
During the rescue, the crew utilized a hoist to lower a rescue technician, followed by a doctor and a nurse, to the base of the rock face. While the crew members were being hoisted, the pilot noticed a cloud of dust near the upper left section of the rock wall. The pilot suspected that the main rotor blades had made contact with the terrain.
Following the operation, the helicopter landed at a nearby base in Pietram to pick up additional rescuers. After a visual inspection by the crew, which revealed white dust on the blades, the pilot decided to continue the flight to Trento Mattarello airport without shutting down the engines. Upon arrival at the destination, a detailed inspection confirmed that the tips of all five main rotor blades had been damaged, with material loss of 7 to 9 cm on each blade and damage to the leading-edge steel protection.
The investigation
The ANSV investigation examined the cockpit voice recorder (CVR) and flight data recorder (FDR) to reconstruct the sequence of events. The investigation focused on the cockpit configuration, the environmental conditions, and the pilot's decision-making process following the suspected impact.
Investigators noted that the HEMS crew member was positioned in the rear cabin to perform hoist operations, leaving the pilot without a co-pilot to assist with obstacle monitoring. The investigation also analyzed the visual challenges posed by the rock face, noting that the yellow-painted tips of the rotor blades tended to blend into the yellowish-grey background of the mountain wall.
Findings
- Primary Cause: The incident was caused by the impact of the main rotor blade tips against a rock wall due to the pilot's inadequate assessment of the distance between the blades and the terrain.
- Organizational Factors: The absence of a crew member in the front seat to assist with obstacle monitoring increased the pilot's workload. The decision to have the HEMS crew member act as the hoist operator (HHO) prevented them from providing essential visual support in the cockpit.
- Environmental Factors: The color of the rock face made it difficult to perceive the rotor disk's proximity, and the lack of an Obstacle Proximity Lidar System (OPLS) meant the pilot had no electronic assistance to detect the nearby wall.
- Human Factors: The pilot experienced a "cognitive gap" following the impact, leading to several high-risk decisions, including continuing the flight at high speeds with damaged blades and failing to perform a thorough engine shutdown and inspection at the first available landing site. The investigation also noted that perceived social and media pressure regarding the operational efficiency of the rescue unit may have influenced the decision to proceed to the main base rather than inspecting the aircraft immediately.