On July 26, 1990, a Fairchild Hiller FH-1100 (registration N442FH) operated by Modern Transportation Mode was involved in an aviation accident near Ozark, MO. Investigators recorded the probable cause as: The failure of the number two turbine shaft bearing during cruise flight, which resulted in a loss of power and a subsequent forced landing with ground contact by the tail rotor. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced a turbine spool-down during cruise, leading to an emergency autorotation that resulted in a tail rotor strike and rollover due to a failed bearing.
What happened
The pilot reported that while the aircraft was operating in cruise flight, a loud pop was heard emanating from the rear section of the helicopter. Immediately following this noise, the turbine engine began to spool down rapidly. In response to the loss of power, the pilot initiated an emergency autorotation with the intention of running onto the landing area.
During the descent and flare phase of the maneuver, the tail rotor struck the ground. This impact caused the aircraft to roll over. The post-accident physical examination of the wreckage confirmed that the failure originated from a broken number two turbine shaft bearing.
The investigation
Examination of the helicopter after the accident revealed mechanical evidence pointing to the source of the in-flight failure. Investigators identified that the number two turbine shaft bearing had failed, which led to the subsequent loss of turbine function and the forced landing sequence.
Probable cause
The failure of the number two turbine shaft bearing during cruise flight, which resulted in a loss of power and a subsequent forced landing with ground contact by the tail rotor.