Incident Overview
A helicopter pilot observed uncommanded torque fluctuations during flight. Shortly thereafter, unusual engine noises prompted the pilot to shut down the engine in flight and execute a forced landing. The pilot had already lowered the collective lever to maintain rotor speed before the engine shutdown, which likely contributed to a successful autorotation and landing. No injuries were reported, and the helicopter sustained only minor damage.
Passenger Safety Intervention
After landing, the pilot intervened to prevent a passenger from exiting the helicopter while the rotors were still turning. This action prevented a potential serious or fatal injury from rotor blade contact, especially given an increased risk of blade sailing at that time.
Post-Inspection Findings
A post-incident inspection revealed that the power turbine governor drive shaft had sheared. Further examination showed that the governor spool bearing had failed, causing the spool bearing guide post to shear. This led to consequential damage to other components within the governor and the failure of the drive shaft.
Component History
The failed spool bearing was a PMA (Parts Manufacturer Approval) part, installed by a third-party repair station when the governor was last overhauled in 2015. While a comparison between the PMA spool bearing and the original equipment manufacturer (OEM) spool bearing revealed discrepancies, it was not determined whether these discrepancies contributed to the bearing failure.