Pilot Debrief

BELL OH58A near Holtville, CA — 2020-07-31

Final reportWPR20LA247
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Date
2020-07-31
Location
Holtville, CA, USA
Aircraft
BELL OH58A
Registration
N901XV
Category
Helicopter
Highest injury
Minor
Fatalities
0
Phase of flight
Maneuvering

Probable cause

The total loss of engine power due to the decoupling of the engine's turbine and compressor sections, which resulted from improper maintenance.

NTSB narrative

The pilot was performing agricultural operations in the helicopter. He made a normal takeoff and completed three passes over the field being sprayed. As he approached wires, the pilot maneuvered the helicopter into a climb and prepared to make a fourth pass. As he was completing a left turn back to the field, the engine experienced a total loss of power. He performed an autorotation, and during the touchdown, the helicopter collided with haystacks. Postaccident examination of the engine revealed extensive damage to the aft end of the compressor, the spur adapter gearshaft, and the compressor splined adapter. A material analysis revealed that the compressor splined adapter had failed in fatigue. The failure decoupled the turbine section from the compressor section resulting in the loss of engine power. The compressor splined adapter failed due to a misalignment of the engine's centerline shafting components that resulted from two separate improper maintenance actions. The first improper maintenance action was the installation of an incorrect number of shims at the interface between the rear compressor diffuser and the accessory gearbox. The second improper maintenance action was the installation of an incorrect compressor splined adapter; the impeller had been machined to fit a larger diameter (-3) compressor splined adapter: however, a smaller diameter (-1) adapter was installed.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Properly shimming the compressor to prevent misalignment and engine failure.

NTSB coding

Evidence available

  • 5 docket documents
View NTSB final reportView NTSB docket

Docket documents5

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