Event Description
During cruise flight, a helicopter unexpectedly rolled 90 degrees to the left. The pilot executed an autorotation and brought the helicopter to a landing, but it rolled over upon touchdown.
Post-Accident Examination
Examination revealed that the left side cabin mount bracket, which holds the intermediate bellcrank for lateral control, had fractured. The fracture surface bore evidence of both overload and fatigue. Additionally, the bellcrank was tight in the cabin mount bracket. The right side cabin mount bracket, which holds the intermediate bellcrank for fore and aft control, had a crack with a fracture surface typical of overload.
Background
The helicopter had previously been involved in a hard landing that resulted in a blade strike on the tail boom. No records were available to indicate what repairs, if any, were conducted following that event.
Manufacturer Statements
According to Enstrom Helicopters, fractures of this type are typically seen following a blade strike. An Enstrom Helicopters service letter specifies that cyclic and collective torque tubes, bellcranks, and fittings are required inspection items following a blade strike.