Pilot Debrief

EUROCOPTER AS350B2 near Pacoima, CA — 2010-11-12

Final reportWPR11FA045
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Date
2010-11-12
Location
Pacoima, CA, USA
Airport
WHP
Aircraft
EUROCOPTER AS350B2
Registration
N1231A
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Initial climb

Probable cause

The contamination of a spool bearing in the power turbine governor during manufacture, which led to the bearing’s failure in flight, a subsequent loss of engine power during departure, and the resultant hard landing.

NTSB narrative

During a downwind departure from the airport, the engine began to lose power. The pilot initiated an immediate autorotation back toward the airport while adjusting the airspeed and flight controls to clear power lines along the airport boundary. After clearing the power lines, the helicopter settled hard on the runway centerline and then began to rock, slide, and yaw right. The pilot attempted to regain control of the helicopter, and it eventually came to a stop upright on its skids facing about 160 degrees right of the runway centerline. The aft portion of the tail boom had separated. Postaccident testing and examination of the engine revealed a degraded power turbine (PT) governor spool bearing. Examinations also revealed the presence of diamond particles, which are used in the manufacturing process for the ball bearings, in the governor spool bearing. It is likely that diamond particle contamination caused the governor spool bearing to fail, which rendered the PT governor incapable of modulating governor servo pressure to the fuel control unit. Although no physical evidence was found indicating that the electronic overspeed system activated, the pilot's statement about two increases in rpm and then a decrease in rpm indicates that the system likely activated. The loss of PT governing ability coupled with the activation of the electronic overspeed system likely resulted in fuel flow oscillations that decreased the fuel flow below the lean blowout limit of the engine and led to the loss of engine power.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the takeoff upon first engine rpm anomaly.

NTSB coding

Evidence available

  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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