Pilot Debrief

Bell 206 near Oakridge, OR — 2019-04-26

Final reportWPR19LA122
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Date
2019-04-26
Location
Oakridge, OR, USA
Aircraft
Bell 206
Registration
N206JH
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Maneuvering

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 narrative

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.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have aborted the final pass after hearing the buzzing sound.

NTSB coding

Evidence available

  • 6 docket documents
View NTSB final reportView NTSB docket

Docket documents6

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