What happened
On October 10, 2009, a Eurocopter AS-350 B3, registration CS-HMI, operated by EMA – Empresa de Meios Aéreos, SA, was deployed by the National Authority for Civil Protection (ANPC) to combat a wildfire in the Duas Igrejas area, Penafiel.
During the operation, the pilot proceeded to the Pedreira Mendes Peixoto quarry to refill the aircraft's Bambi Bucket using a small rainwater pool. As the helicopter began its takeoff and climb with a full bucket, it encountered sudden turbulence, likely caused by thermal currents common in quarry environments. This turbulence drifted the aircraft toward its right, placing it on a collision course with medium-voltage power lines positioned at the two o''clock position.
Although the pilot attempted an evasive maneuver to the left, the tips of the main rotor blades struck and severed three electrical cables. The impact caused the helicopter to bank sharply to the right. To prevent the tail rotor from contacting the lines, the pilot executed an emergency discharge of the Bambi Bucket and transitioned the engine to idle to mitigate severe vibrations caused by the damaged rotor blades. The pilot successfully performed an emergency landing in an obstacle-free area near the refueling site. There were no injuries to the crew, though the impact caused damage to the cockpit glass and the power lines, leading to local electricity outages.
The investigation
The GPIAAF investigation examined the flight path and the environmental conditions at the quarry. The investigation established that the power lines, situated approximately 30 meters above the ground, ran perpendicular to the helicopter's flight path. It was noted that while the pilot focused on the initial power pole, the cables connecting to a second pole on the left were difficult to perceive. The investigation also assessed the impact of thermal instability in the quarry area on the aircraft's stability during the critical takeoff phase.
Findings
- The primary cause of the incident was the collision with electrical cables while operating in turbulence that the pilot had not anticipated during the takeoff phase.
- The sudden turbulence was likely generated by thermal currents resulting from the intense solar radiation and temperature contrast within the quarry.
- The pilot's attention was focused on the primary power pole, leading to a failure to notice the perpendicular cables extending from the adjacent pole.
- The aircraft sustained damage to the main rotor blades and the cockpit windscreen due to the whip effect of the severed cables.