What happened
On May 23, 2010, an AS 350 B3 helicopter, registration EC-LBF, was performing a non-commercial flight near Becerril de la Sierra, Madrid. The pilot, who was on duty at the Madrid Fire Department's emergency helicopter base, had decided to conduct an accommodation flight. The aircraft was carrying five passengers.
During the flight, approximately 1,0/00 ft above the ground, the pilot executed a left turn followed by a right turn. During the execution of the right turn, the pilot experienced heavy controls and a loss of altitude accompanied by an increase in airspeed. The aircraft entered a steep descent and a nose-down attitude. In an attempt to recover, the pilot applied significant back cyclic, initiating a flare that brought the aircraft to a level attitude just meters above the ground. However, the tail section of the aircraft struck the terrain, causing the tail boom to detach and the helicopter to spin violently around its vertical axis before coming to rest.
The investigation
The investigation examined the aircraft's flight path, wreckage distribution, and engine data. Analysis of the wreckage revealed that the aircraft's lower wire strike protection system had come into contact with a wire fence, which was found broken at the site. The impact of the tail boom against the ground was confirmed by tracks in the vegetation.
Data extracted from the Vehicle and Engine Management Display (VEMD) and the Digital Engine Control Unit (DECU) showed no mechanical failures or abnormal engine performance prior to the accident. The investigation also noted that the fuel cut-off lever was found in the closed position; it was determined that a passenger may have inadvertently moved this lever while attempting to brace for impact. The investigation concluded that the engine remained operational until the final moments of the impact.
Findings
- The primary cause of the accident was the failure to maintain a minimum safe altitude above the terrain.
- The execution of a turn with a bank angle exceeding standard limits and a high rate of descent contributed to the collision with the ground.
- The impact with the wire fence caused damage to the lower wire strike protection system.
- The detachment of the tail boom resulted in the loss of anti-torque control, leading to the subsequent spinning of the aircraft.