What happened
On September 19, 2011, an Agusta AB-412, registration EC-JRY, operated by FAASA Aviación, S. A., was performing a positioning flight from Palma del Río to Alhama de Almería. The flight was conducted in two stages, with the second stage being flown under visual flight rules.
During the second leg of the flight, a critical failure occurred within the main transmission system. The aircraft was flying at approximately 120 knots and 2/00 meters (656 feet) above the ground when the failure occurred. This mechanical breakdown caused the main rotor to lose torque from the engines, while the tail rotor continued to function as it remained connected to the engine power. This imbalance induced an immediate left yaw.
The pilot attempted to respond to the emergency by initiating an incomplete autorotation maneuver. However, the loss of lift and the aerodynamic effects of the vertical stabilizer at lower speeds made the aircraft uncontrollable. After approximately eight seconds, the helicopter struck a ridge, causing the tail skid and rotor blades to impact the terrain. The impact triggered a significant fire that consumed the wreckage and surrounding vegetation. There were 3 fatalities among the occupants, including two crew members and one passenger.
The investigation
The CIAIAC investigation focused on the mechanical integrity of the main gearbox (MGB) and the flight dynamics following the loss of torque. Investigators utilized sound spectrum analysis from the Cockpit Voice Recorder (CVR) to identify frequency alterations related to the lower planetary gears.
Physical examination of the MGB revealed that the gears in the lower planetary stage had failed. This failure effectively disconnected the main rotor mast from the drive train. The investigation also analyzed the flight data recorder (FDR) to reconstruct the aircraft's trajectory and the pilot's control inputs. While the fire heavily damaged the wreckage and complicated the recovery of certain flight parameters, the investigation successfully established the mechanical sequence of the failure.