Pilot Debrief

GARLICK HELICOPTERS INC UH 1H near Cove, OR — 2015-05-31

Final reportWPR15LA178
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Date
2015-05-31
Location
Cove, OR, USA
Aircraft
GARLICK HELICOPTERS INC UH 1H
Registration
N462CC
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Maneuvering

Probable cause

The failure of the engine-to-transmission drive shaft coupling assembly due to a fatigue fracture of one of its attachment bolts, which resulted in a loss of power to the main rotor.

NTSB narrative

The commercial pilot reported that, while maneuvering the helicopter at low altitude during logging operations, he felt a vibration and heard a howling sound coming from the transmission area. He immediately initiated a precautionary landing; however, as the helicopter settled to the ground, the main rotor rpm dropped, and the pilot attempted to cushion the landing with aggressive collective input. The helicopter subsequently landed hard. Postaccident examination revealed multiple fractures of the Kaflex engine-to-transmission drive shaft coupling assembly. According to the flight manual, a failure of the engine-to-transmission drive shaft would lead to a complete loss of power to the main rotor. The coupling assembly failure was initiated by the failure of an attachment bolt due to a fatigue crack on the flange section that attached the coupling assembly to the transmission shaft flange. No evidence of any material anomalies were found in the fractured bolt, and the fatigue crack was likely caused by the severe stress imposed by logging operations. The manufacturer did not specify a replacement interval for the bolt. The investigation could not determine when the fatigue crack developed and propagated; therefore, it could not be determined whether the crack would have been identified during an annual inspection.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have conducted a precautionary landing earlier after initial vibrations.

NTSB coding

Evidence available

  • Video
  • 10 docket documents
View NTSB final reportView NTSB docket

Docket documents10

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