Pilot Debrief

Bell OH-58A near Brawley, CA — 2023-11-21

Final reportWPR24LA041
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Date
2023-11-21
Location
Brawley, CA, USA
Airport
KBWC
Aircraft
Bell OH-58A
Registration
N158TR
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Initial climb

Probable cause

A total loss of engine power due to the failure of the No. 8 bearing and the subsequent failure of the scavenge oil pump.

NTSB narrative

The pilot was conducting agricultural operations at night and had just departed from a company loading area. About 150 ft above ground level (agl), the pilot experienced a sudden power surge, abnormal engine noise, and vibration. The pilot believed that engine failure was imminent and turned back toward his point of departure. Engine power decayed, and the pilot bled off rotor rpm to maneuver over terrain toward flat ground. The helicopter landed hard, entered a pylon whirl condition, and the main rotor hub assembly separated from the main rotor mast. Postaccident examination of the airframe revealed no evidence of preaccident mechanical malfunction or failure. However, postaccident examination revealed a sheen of oil beneath the engine and that the engine’s compressor (N1) and power turbine (N2) systems were seized. Further examination of the engine revealed multiple failed bearings, failed drives, and fractures within the turbine scavenge oil pump assembly. The engine had been installed on the helicopter about 10 flight hours before the accident. Based on metallurgical analysis of the engine components, the No. 8 bearing likely failed and shed debris to the oil pump, which bound the first level oil pump gears and led a gear tooth to fracture and the pump driveshaft to fail. Subsequently, the engine was starved of oil and lost all power. The cause of the bearing failure could not be determined.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the flight after the initial power surge.

NTSB coding

Evidence available

  • 8 docket documents
View NTSB final reportView NTSB docket

Docket documents8

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