NTSB Identification: LAX00LA239.
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Accident occurred Friday, June 23, 2000 in ARBUCKLE, CA
Probable Cause Approval Date: 09/26/2001
Aircraft: Bell UH-1B, registration: N807SB
Injuries: 1 Fatal.

NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter pilot took off about 0415 from a chemical loading site, made a left turn, and departed to spray a sunflower field. Subsequently the wreckage was located 1/2 mile west of the field. The helicopter collided with level farm terrain while in a descent. The horizontal and vertical stabilizers and tail rotor assembly appeared to be undamaged. The main rotor mast had rotated about 45 degrees forward, and symmetrical upward crushing of the cabin area occurred. A postaccident examination of the helicopter was conducted. The anti-torque control system examination revealed a tail rotor pitch change shaft's AN320 castellated shear nut stripped from the rotor end of the shaft. The threads were still intact on the shaft but missing from the nut. The shaft cotter pin hole retained the sheared portions of the cotter pin. The shearing force came from an unknown source. An ongoing wear imprint from the shaft end, into the castle nut, was noted by the lab report. Nut damage to the interior of the pitch change cap was also found during the wreckage examination.

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

the partial failure of the tail rotor pitch change control rod that resulted in an attempted run-on landing in dark night conditions.

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