NTSB Identification: LAX00TA163.
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Accident occurred Thursday, April 20, 2000 in GREEN VALLEY, AZ
Probable Cause Approval Date: 11/01/2001
Aircraft: Hughes OH-6A, registration: N61869
Injuries: 1 Minor.

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

While maneuvering about 20 feet above obstacles looking for the footprints of a group of suspected illegal entrants, the U.S. Border Patrol pilot suddenly experienced an unusual vibration in the cyclic control. After the vibration started, the helicopter almost immediately started turning right and descended. The pilot attempted to stop the turn and descent, but to no avail, and he crashed in the rough terrain. The previous day a 300-hour inspection had been completed by Border Patrol mechanics, and it involved a rebuild of the swashplate assembly. During this maintenance, the cyclic control's longitudinal link (part number 369A7608) was removed and replaced at the stationary swashplate. Upon completion of the maintenance, a cotter pin is required to be installed in the link's attachment nut to secure it. The cotter pin, and the respective nut, were observed missing at the accident site. During the recent maintenance, a mechanic had failed to reinstall the cotter pin into the nut, and it backed off during flight. This maintenance oversight-related failure resulted in the pilot's complete loss of cyclic control.

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

Company maintenance personnel's failure to secure an attachment nut to a control link. While maneuvering, the parts separated and resulted in the total cyclic control system failure and impact into rough terrain.

Full narrative available

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