Agusta A109A, G-DNHI
During cruise flight, an engine exhaust duct separated from the helicopter and struck the tail rotor assembly, causing the tail rotor gearbox to also separate. After an initial yaw to the right, the pilot regained limited control. However, a further sudden yaw, possibly associated with a partial structural failure of the upper vertical stabiliser, prompted an immediate autorotative descent, which culminated in a successful forced landing. The investigation established that a clamp attaching an exhaust duct to the left engine had failed, due to stress corrosion cracking, allowing the duct to disconnect from the engine. Two safety recommendations are made.
Published 10 December 2014