What happened
On August 12, 2010, at approximately 19:38 local time, an EUROCOPTER AS 350 B3, registration F-GYBH, was engaged in aerial firefighting operations near La Braña, León. The aircraft, operated by Coyotair, was performing water drops to support efforts against an active wildfire in a valley characterized by rugged terrain and high temperatures.
During a water drop maneuver, the pilot was flying at an indicated airspeed of 60 knots and an altitude of approximately 50 feet. While preparing to release the water load, the helicopter encountered sudden turbulence and a strong downdraft, which caused the aircraft to lose altitude and enter a thick mass of smoke.
In an attempt to avoid the terrain, the pilot initiated an evasive maneuver by turning left and increasing collective pitch while releasing the water load to reduce weight. However, as the aircraft approached the mountainside, the pilot applied aft cyclic to raise the nose. This maneuver caused the tail of the helicopter to descend toward the vegetation, resulting in the tail rotor blades striking an object, potentially the chain of the water bucket (helibalde). The water bucket also struck rocks on the ground. Following the impact, the pilot noted a sudden left yaw but managed to maintain control and return to base.
The investigation
The investigation focused on the meteorological conditions and the pilot's flight maneuvers. Investigators examined the thermal gradients present in the valley, noting that the combination of irregular topography and high temperatures near the flames creates significant convective currents and turbulence. The prevailing winds, primarily from the north and west, were hitting the mountains perpendicular to the valley's axis, further exacerbating turbulent conditions.
Technical analysis of the aircraft revealed damage to the tail rotor blades, including bent blade tip indicators, and damage to the water bucket, which showed tears and signs of being dragged. The investigation also reviewed the pilot's flight experience, noting that while the pilot had significant total flight time, the majority of that experience was in much simpler aircraft types (Robinson R-22 and R-44) and the experience specifically in the EUROCOPTER AS 350 B3 and in mountain firefighting operations was limited.
Findings
- The tail rotor blades struck an object, likely the chain of the water bucket, during an evasive maneuver following an unexpected loss of altitude.
- The pilot's maneuver to raise the nose via aft cyclic caused the tail to descend into the path of the obstacle.
- Limited pilot experience in the specific aircraft type and in mountain flying acted as a contributing factor to the outcome of the maneuver.
- High temperatures and complex terrain created severe turbulence and downdrafts that triggered the initial loss of altitude.