Incident Overview
On August 23, 2005, at approximately 13:45 local time, a Bell 206 L4 helicopter with registration EC-JKG was involved in an incident near the Borbollón reservoir in Hoyos, Cáceres. The aircraft was operated by Helicópteros del Sureste, S. A., and was powered by a single Rolls-Royce 250-C30P engine. The flight was a general aviation training exercise involving dual command, with an instructor pilot and a student pilot on board.
Operational Context
The crew was conducting a simulated tail rotor failure maneuver, a special procedure classified in the operator's operations guide. This exercise requires maintaining directional control on the ground by managing collective and throttle inputs while the pedals are fixed. The landing zone was selected by the instructor after a reconnaissance flight, described as a wide, obstacle-free area within the reservoir's flood perimeter.
Sequence of Events
During the maneuver, the helicopter made contact with the soft terrain. The right skid sank into the ground, prompting the instructor to adjust the collective to prevent further sinking. This action caused the aircraft to lift off the ground approximately one meter. Subsequently, the helicopter initiated an uncontrolled turn to the right and experienced a hard landing. The pilot reported that the main rotor speed (Nr) dropped below 85% during this sequence.
Damage Assessment
Post-incident inspection revealed significant damage to the aircraft. The tail cone exhibited a break and severe wrinkles approximately 50 cm from its attachment point to the fuselage. The first section of the tail rotor transmission shaft was fractured, and the control rods for the tail rotor and horizontal stabilizer were bent. Additionally, one main rotor blade sustained a strike near the outer tip, and the left vertical fin of the horizontal stabilizer showed impact damage with a rearward break.
Contributing Factors
The investigation noted that Bell Helicopter had issued an Operations Safety Notice (OSN 206-84-10) in 1984 warning about potential tail cone deformation during autorotations or rapid stops. Although this notice technically applied to earlier versions, it was considered applicable to the L4 model. The instructor and student were unaware of this specific safety notice at the time of the incident.