Bell 206 N206JH accident near Oakridge, Oregon

Probable cause

A total loss of engine power following the failure of a 3rd stage turbine blade due to low- and high-cycle fatigue.

NTSB analysis

During the agricultural aerial application flight, the helicopter lost engine power, and the pilot performed an autorotation into sloping, tree-covered terrain.

Examination of the engine revealed that a blade from the 3rd stage turbine wheel had been liberated, resulting in the loss of engine power. The blade’s fracture surface indicated that it was initiated in a low-cycle fatigue mode near the trailing edge radius of the blade and progressed to a high-cycle fatigue process along the blade chord, which finally resulted in overload failure.

The initiation event for the failure could not be determined; however, it was likely caused by operation within an engine speed avoidance range, an engine speed/airframe interaction of unknown origin, inadequate engine temperature management on startup, inadequate wheel design or undetermined manufacturing defect, or combinations thereof. The blade had not been operated beyond its overhaul or inspection time limit.

Similar blade failure was associated with five previous accidents and two previous incidents. An in-service replacement program was started by the engine manufacturer on July 30, 2021, requiring removal and replacement of the 3rd stage turbine wheel with a new design at the next scheduled replacement time.

Text from the NTSB. Open the NTSB docket for WPR19LA122 for the full record.