NTSB Identification: WPR12LA115
14 CFR Part 137: Agricultural
Accident occurred Wednesday, February 22, 2012 in Farmington, CA
Probable Cause Approval Date: 10/09/2014
Aircraft: TEXAS HELICOPTER CORP OH-13E/M74, registration: N43921
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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. 

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

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.

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