What happened
On July 28, 2011, an Eurocopter AS-350B3, registration CS-HMI, operated by EMA – Empresa de Meios Aéreos, was engaged in aerial firefighting operations near Valongo. After replenishing its water bucket at a stream approximately 3NM from the wildfire, the pilot began a climb to transit to the fire site. During this maneuver, the pilot failed to detect high-voltage power lines crossing the valley.
Upon realizing the proximity of the cables, the pilot determined there was insufficient lateral clearance to deviate and insufficient performance to clear the lines from above. In an attempt to fly beneath the wires, the aircraft struck two cables, which were severed by the main rotor blades and the mast. While the collision did not alter the flight characteristics of the aircraft, the pilot elected to perform a precautionary landing nearby to await maintenance inspection.
The investigation
The GPIAAF investigation examined the flight history, environmental conditions, and crew fatigue levels. The pilot had been on duty since 08:15 UTC, performing a high-intensity mission that included 54 water drops and 21 landings, many of which occurred in unprepared terrain under low visibility due to smoke. The investigation also noted that the cables lacked any visual marking or signaling devices.
Findings
- The collision was likely caused by a loss of pilot concentration, preventing the timely detection of the power lines.
- Contributing factors included the lack of marking/visibility on the high-voltage cables and the accumulation of pilot fatigue following an intense period of flight service.
- Environmental conditions, specifically persistent smoke and high temperatures, increased the cognitive workload and reduced visibility.
- The pilot had been performing demanding operations for over 11 hours of service across two consecutive days of heavy firefighting activity.