Agusta A109S Grand, G-CGRI
During the cruise, some four minutes into the flight, the helicopter suffered severe vibration. The pilot carried out an autorotation and landed safely. Subsequent investigation revealed that one of the two tail-rotor trunnion flange caps had separated, causing damage to the tail-rotor blade and vertical fin. The metallurgical examination showed the failure to be due to an initial clockwise torsional overload followed by a final axial tensile overload. It is possible that the initial clockwise torsional overload was applied either during the initial manufacture of the helicopter or during maintenance activity during the night prior to the incident flight. The maintenance manual did not contain the specific torque loading for the trunnion flange caps. The helicopter manufacturer has since issued torque loading figures for the flange caps and has amended the maintenance manual accordingly.
Published 10 December 2014