Pilot Debrief

BELL UH-1H near Chapelle, NM — 2022-07-17

Final reportCEN22FA317
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Date
2022-07-17
Location
Chapelle, NM, USA
Aircraft
BELL UH-1H
Registration
N911SZ
Category
Helicopter
Highest injury
Fatal
Fatalities
4
Phase of flight
Descent

Probable cause

The total loss of engine power due to the fatigue failure of the starter-generator input (zerol) gear which failed due to poor maintenance. Contributing to the accident was the unsuccessful autorotation complicated by the setting sun and high density altitude.

Contributing factors

Contributing to the accident was the unsuccessful autorotation complicated by the setting sun and high density altitude.

NTSB narrative

The pilot of the helicopter, two tactical flight observers, and a rescue specialist were returning to their home airport after conducting firefighting operations. While in a west-bound cruise flight about 500 to 600 ft about ground level (agl), the helicopter entered a descent that rapidly increased to over 5,000 ft per minute, and impacted terrain in a tail-low attitude. The helicopter was destroyed during the impact with terrain. Examination of the engine revealed that the starter-generator input (zerol) gear failed due to fatigue. This failure led to the starter-generator driveshaft shearing, N1 accessory gearbox seizure, and a total loss of engine power. An examination of the remaining helicopter systems revealed no mechanical anomalies that would have precluded normal operations. About 17 flight hours before the accident, an engine chip event occurred, and a small piece of ferrous metal was found on the magnetic chip plug. Following the chip event the oil system was drained and flushed and the filter elements were removed, cleaned, and reinstalled. No further engine chip lights were reported after the engine chip event. The chip and oil sample were shipped to a lab for analysis. The results of the lab analysis were not used by the operator to troubleshoot the reason for the chip event. Had the operator conducted an analysis, they could have potentially identified the deteriorating component and impending failure. The helicopter’s low altitude (500 to 600 ft agl) during the return leg made the transition from powered flight to autorotation after an unexpected loss of engine power more time critical. The high density altitude conditions, combined with flight directly into the setting sun, may have contributed to the unsuccessful autorotation following the total loss of engine power.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Maintenance should have conducted thorough analysis after previous engine chip event.

NTSB coding

Evidence available

  • ADS-B / radar
  • Photos
  • 27 docket documents
View NTSB final reportView NTSB docket

Docket documents27

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