Pilot Debrief

S.N.I.A.S. AS-350B ECUREUIL near Hamilton, MT — 2013-07-01

Final reportWPR13LA302
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Date
2013-07-01
Location
Hamilton, MT, USA
Airport
6S5
Aircraft
S.N.I.A.S. AS-350B ECUREUIL
Registration
N989WC
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Cruise

Probable cause

The loss of engine power during cruise flight due to the fatigue failure of a pneumatic fuel controller pipe. Also causal was maintenance personnel’s failure to adequately maintain the pipe and replace it with a thicker type.

NTSB narrative

The pilot reported that, about 20 minutes after departure, the helicopter lost all engine power during cruise flight. The pilot performed an autorotation into a small forest clearing. During the landing sequence, the helicopter sustained substantial damage. Examination of the engine revealed that the pneumatic fuel controller (P2) pipe that delivered air pressure from the centrifugal compressor to the fuel control unit (FCU) had separated at the FCU fitting. The P2 pipe's failure allowed ambient air pressure to enter the line and resulted in the FCU commanding the engine to spool down to ground idle speed. The pipe exhibited deformation due to bending damage and signatures indicating that it was making contact with its union fitting at the FCU. The P2 pipe was a thin-walled type, which the engine manufacturer had recommended be replaced with a thicker version 29 years previously. Further, the engine manufacturer had issued multiple service letters advising maintenance personnel of the correct procedures for fitting, inspecting, and maintaining such air lines. The pipe's fracture surfaces at the separation point exhibited signatures consistent with fatigue as a result of noncompliance with the manufacturer's recommendations.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Performing maintenance checks on the P2 pipe before the flight.

NTSB coding

Evidence available

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

Docket documents6

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