What happened
On July 24, 2005, a Eurocopter AS 350 B2, registration F-GTHR, was engaged in wildfire suppression operations near Paradinha, in the municipality of Moimenta da Beira. The aircraft, operated by Helisul, had been deployed from Armamar to support the National Service for Firefighting and Civil Protection (SNBPC).
After transporting a firefighting brigade to the site and performing an initial water drop, the pilot attempted a recovery maneuver. During this phase, the helicopter's right skid struck high-voltage electrical transmission lines. The impact caused the cables to snap and slide along the skid, eventually becoming entangled with the aircraft. The tension from the cables pulled the helicopter into a violent rotation, which caused the cables to snag the tail boom, resulting in its structural failure and separation from the main fuselage.
As the aircraft lost directional control, the pilot shut down the engine and performed a forced landing to mitigate the impact. The helicopter struck the ground near the fire, causing significant damage to the airframe, including a fractured cockpit ceiling, damaged main rotor blades, and the separation of the tail rotor assembly. Despite the severity of the crash, the pilot emerged uninjured.
The investigation
The GPIAAF investigation focused on the visibility of the obstacles and the coordination of the ground operations. Investigators established that the 20 KVA power lines were not marked on available aeronautical charts. Furthermore, the transmission poles lacked high-visibility paint, and the presence of smoke from the active wildfire significantly obscured the thin wires.
The investigation also examined the role of the ground operational coordinator, who was responsible for informing the pilot of obstacles in the area. It was determined that the coordinator had not communicated the presence of the power lines to the pilot. The aircraft's maintenance records were found to be in order, and the pilot was fully qualified for the mission.
Findings
- The primary cause of the accident was the loss of control following a collision with electrical transmission lines.
- The lack of marking for the power lines on operational charts contributed to the collision.
- Poor visibility of the lines was caused by the lack of high-visibility markers on the cables and the lack of contrasting paint on the poles, a situation exacerbated by heavy smoke from the wildfire.
- The failure of the ground operational coordinator to identify and communicate the presence of the obstacle to the pilot was a contributing factor.
- The entanglement of the cables with the tail boom led to the structural failure of the tail section and the subsequent loss of directional control.
Safety action
Based on the findings, the investigation issued several recommendations to the National Service for Firefighting and Civil Protection (SNBPC):
- Mandate the installation of "wire cutter" systems on helicopters used for firefighting to protect the main rotor and landing gear.
- Implement training for ground brigade coordinators to emphasize the identification and communication of obstacles to pilots.
- Promote local-level initiatives to ensure electrical transmission lines and poles are properly signaled with high-visibility markers.