Pilot Debrief

TEXAS HELICOPTER CORP OH-13E/M74 near Farmington, CA — 2012-02-22

Final reportWPR12LA115
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Date
2012-02-22
Location
Farmington, CA, USA
Aircraft
TEXAS HELICOPTER CORP OH-13E/M74
Registration
N43921
Category
Helicopter
Highest injury
Serious
Fatalities
0
Phase of flight
Maneuvering

Probable cause

The in-flight separation of the wood portion of one main rotor blade while maneuvering at low level, the reason for which could not be determined because postaccident examination did not reveal any anomalies that would have precluded normal operation.

NTSB narrative

The commercial pilot was conducting aerial application flights in the single main rotor helicopter over a flat, level agricultural field. He had already conducted several uneventful flights that day in the helicopter on other portions of the same field. Just as the pilot completed a course reversal turn, the helicopter crashed in the field. The turn was the last thing the pilot remembered about the flight, and there were no eyewitnesses. Although the field was soft, and the helicopter's airspeed and altitude were low, the helicopter was extensively fragmented. One main rotor blade was found about 500 feet from the rest of the wreckage. That wood main rotor blade was essentially intact, except for the absence of its metal core and multiple linear, spanwise fastener tearouts at the root. The core was fracture-separated in overstress from its blade grip and was bent in a 270-degree arc. All these signatures were consistent with the wood blade, minus the core, separating from the rotor hub while in flight. The loss of the blade, and the subsequent imbalance to the rotor disc, induced vibratory loads that exceeded the structural strength of the helicopter, and resulted in extensive fragmentation of the helicopter before ground impact. No damage patterns consistent with a ground rotor strike were observed. The incompleteness of the maintenance records prevented the determination of the service history of the failed blade as well as its compliance with required inspections. The reason for the failure of the blade wood could not be determined.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Proper inspection and maintenance of the main rotor blades could have prevented the accident.

NTSB coding

Evidence available

  • 11 docket documents
View NTSB final reportView NTSB docket

Docket documents11

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