Pilot Debrief

BELL 47G 2 near Oshkosh, WI — 2016-07-30

Final reportCEN16LA294
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Date
2016-07-30
Location
Oshkosh, WI, USA
Airport
OSH
Aircraft
BELL 47G 2
Registration
N975BH
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Descent

Probable cause

The loosening and separation of the throttle linkage nut, which resulted in a loss of throttle control and subsequent hard landing after autorotation.

NTSB narrative

The airline transport pilot maneuvered the helicopter on the downwind leg of the airport traffic pattern and attempted to reduce power for landing; however, the engine power remained excessively high. The pilot attempted to further reduce the engine power by turning off one magneto and applying carburetor heat, but the power remained too high to safely descend. The pilot then entered a sideslip, which allowed the helicopter to descend to about 100 ft above the runway. He turned the engine power off and autorotated to the ground. The helicopter landed hard in a tail-low attitude. The main rotor struck the tail and the tail rotor assembly separated from the helicopter. A postaccident examination found that the throttle linkage nut had loosened and separated from its fitting, causing the throttle to remain open. The helicopter's maintenance manual did not specify a torque value for the throttle linkage nut, and there were no maintenance procedures requiring the nut to be loosened or removed during overhaul. The pilot indicated that a complete overhaul of the helicopter was completed about 37 hours before the accident flight.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have conducted a go-around instead of attempting to land with power loss.

NTSB coding

Evidence available

  • Photos
  • 2 docket documents
View NTSB final reportView NTSB docket

Docket documents2

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