Accident report after fractured rotor hub
May 27, 2011
The Swedish Accident Investigation Board (Statens haverikommission, SHK) has published its report after an accident that occurred on 28 October 2009 at Flatruet Härjedalen, involving a helicopter with registration SE-JME.
The helicopter, an EC 120B Colibri, was performing a commercial air transport in the mountainous area between Helags and Funäsdalen when the pilot heard a loud bang and felt very strong low-frequency vibrations in the helicopter. It was not possible to read the instruments, and parts of the interior fittings had become detached, why the pilot entered an autorotation and landed safely.
The post-landing inspection found a large open crack in the main rotor hub along with several cracks in the tail section and the tail boom.
The Investigation Board has determined that the accident was caused by the fact that the maintenance system for the helicopter model did not detect this type of defect because the time from initiation of the crack to final fracture is shorter than the inspection interval.
EASA is recommended to work towards a more sensitive method aimed at detecting any defects in the main rotor hub at an earlier stage than those described in an EASA AD.