What happened
On September 14, 2009, at approximately 10:30 local time, a EUROCOPTER AS-350-B3 helicopter, registration EC-LBV, was dispatched to assist in firefighting efforts near Vilamartín de Valdeorras, Ourense. The aircraft, operated by INAER, was transporting a firefighting brigade and an external water tank (helibucket) to combat a forest fire.
After delivering the crew to the fire site, the pilot proceeded to the Sil River to perform water collection maneuvers. The aircraft successfully completed two water pickups. However, during the third attempt, while performing a takeoff maneuver from a hover, the helicopter struck a 20,000 V medium-voltage power line that crossed the river at a height of approximately 20 meters.
The impact caused the cable to sever, dragging across the aircraft's VHF antenna and engine cowling before snagging the pitch actuator. The pilot, managing a heavy load of 1,050 kg, released the water tank to mitigate the situation and performed aggressive control inputs to stabilize the aircraft. Despite the impact, the pilot managed to land the aircraft safely at a nearby location. The severed power line fell onto a roadway, damaging two parked vehicles and causing a power outage for several local communities.
The investigation
The CIAIAC investigation focused on the flight planning, the execution of the takeoff maneuver, and the pilot's situational awareness. The investigation examined the flight logs, which showed the aircraft's movements, and interviewed the pilot regarding the sequence of events. Investigators also reviewed the aircraft's flight manual specifications for external load operations and compared the actual flight path during the third water pickup to the standard takeoff procedures.
Findings
- The pilot had not performed an adequate reconnaissance of the area to identify potential obstacles, likely due to a lack of familiarity with the specific working zone.
- The flight planning was deficient; the pilot prioritized a rapid response to the emergency over the necessary preparation and route planning required for VFR operations.
- The pilot's attention was partially diverted by the coordination with a second helicopter operating in the same area, leading to a failure to notice the power lines despite having operated in the vicinity twice previously.
- The takeoff maneuver was executed with a flight path gradient of only 4%, which is significantly lower than the 12% gradient recommended by the flight manual for a standard takeoff at 40 knots.
- The primary cause was a combination of inadequate terrain reconnaissance and an improper takeoff maneuver gradient.