Pilot Debrief

BELL BHT407 near Big Fork, MT — 2013-04-25

Final reportWPR13TA205
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Date
2013-04-25
Location
Big Fork, MT, USA
Airport
S27
Aircraft
BELL BHT407
Registration
N937GR
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Maneuvering

Probable cause

The pilot’s failure to maintain helicopter control while maneuvering over mountainous terrain in strong up/downdrafts and possible mountain wave activity, which resulted in a loss of tail rotor effectiveness.

NTSB narrative

The pilot reported that, while conducting a reconnaissance orbit over mountainous terrain, he crossed over a ridgeline and then lost directional control of the helicopter. He applied full left pedal and lowered the nose and collective in an attempt to regain control. The helicopter subsequently impacted the uneven snow-covered terrain and rolled onto its right side. Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunction or failures that would have precluded normal operation. A weather study for the area around the accident site revealed that the temperature profile and windy environment supported strong up/downdrafts with the potential for mountain wave formation near the altitude at which the flight was maneuvering. It is likely that the pilot was unable to maintain control of the helicopter as a result of a loss of tail rotor effectiveness while operating in the high-altitude environment and in an area with strong up/downdrafts and possible mountain wave activity.

Analysis

Primary failure mode
Loss of control
First missed decision gate
Pilot could have avoided maneuvering in high wind conditions near the ridge line.

NTSB coding

Evidence available

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

Docket documents5

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