NTSB Identification: LAX00FA306.
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Accident occurred Friday, August 18, 2000 in WATSONVILLE, CA
Probable Cause Approval Date: 03/30/2004
Aircraft: Robinson R22 BETA, registration: N8313Z
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The flight instructor was cruising or maneuvering the helicopter during an introductory flight with a new student. Witnesses in the area reported observing the helicopter in what appeared to be normal flight, heard a loud bang, and then saw the helicopter abruptly pitch nose down while the main rotor blades separated from the helicopter. One of the witnesses observed the helicopter turn and climb moments before the accident sequence initiated; two of the witnesses reported that just prior to the accident the helicopter was flying in level cruise flight. At the time of the accident, the sky was clear, the visibility was at least 10 miles, a light breeze existed, and no other aircraft were flying in the immediate area. The on-scene examination of the accident site revealed Plexiglas fragments and left door components about 400 feet from where the main wreckage fell into an open dirt field. Additional items, including sunglasses, a left skid tube-mounted component and the main rotor blade assembly, were found 140 to 330 feet from the main wreckage. An examination of the rotor hub revealed the teetering stops were cracked and both of the rotor blade spindles had broken their respective (droop stop) tusks. The physical evidence indicates the main rotor diverged from its normal plane of rotation, resulting in mast bumping, main rotor blade contact with the fuselage, and separation of the main rotor assembly. No evidence of any preimpact mechanical malfunction was found with the helicopter. The initiating event that produced the main rotor divergence could not be determined.

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

The divergence of the main rotor from its normal plane of rotation for an undetermined reason, which resulted in mast bumping and rotor contact with the fuselage.

Full narrative available

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