What happened
On August 6, 2003, at approximately 20:50 local time, a Bell 206 L3 helicopter, registration D-HALT, was performing a firefighting mission in the Garganta de la Olla area of Cáceres, Spain. The aircraft had landed on a hilltop in the Sierra de Tormantos to embark six forest firefighters.
Shortly after takeoff, once the aircraft had reached an altitude of approximately one meter, it began a continuous, unintended right-hand turn. During this maneuver, the helicopter entered a descent. After completing three rotations, the aircraft impacted the ground. The accident resulted in one fatality among the crew and six injuries among the passengers.
The investigation
The investigation examined the flight conditions, the aircraft's weight, and the meteorological data provided by the pilot. At an altitude of 5,000 feet, the reported weather consisted of a north wind and a temperature of 25 °C. At the time of takeoff, the aircraft's weight was 3,800 lb.
The pilot reported that immediately after lifting off, a sudden and unpredictable tailwind—opposing the prevailing headwind—caused the aircraft to enter an uncommanded right-hand rotation. The investigators analyzed the aerodynamic conditions, specifically focusing on the aircraft's low airspeed and the impact of the wind shift on the tail rotor's performance.
Findings
- The investigation established that the accident was caused by Loss of Tail Rotor Effectiveness (LTE), manifesting as an inadvertent rightward yaw.
- A sudden tailwind acted as an accelerator for the yaw rate, initiating the uncontrolled rotation.
- The aircraft was operating at a low airspeed (between a hover and 30 knots), a condition that significantly increases the risk of LTE.
- The combination of low airspeed and the sudden change in wind direction prevented the pilot from maintaining directional control, leading to the impact.