NTSB Identification: LAX00TA006.
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Accident occurred Thursday, October 07, 1999 in MORENO VALLEY, CA
Probable Cause Approval Date: 04/25/2001
Aircraft: McDonnell Douglas 369E, registration: N991SD
Injuries: 3 Uninjured.

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

The Sheriff's Department helicopter was orbiting over ground based law enforcement activity. It was a dark night and the winds aloft were 20 to 25 knots at 500 feet agl. The pilot said he was attempting to shine the helicopter's spotlight on a vehicle; however, the wind kept blowing the helicopter past the location on each of the first two orbits. On the third orbit, the pilot inadvertently allowed the helicopter to slow below translational lift speed and the helicopter yawed 180 degrees to the right uncontrollably. The pilot momentarily recovered directional control of the helicopter but then the right yaw resumed. He made several more attempts to recover directional control of the helicopter but when he saw the altitude becoming low, he flew to a pre-selected landing zone where the helicopter landed hard while in a right yawing spin. During the landing the main rotor blades severed the tail boom and the helicopter came to rest on its right side.

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

The failure of the pilot to maintain sufficient forward airspeed to preclude an inadvertent encounter with loss of tail rotor effectiveness, which resulted in a loss of yaw control. The pilot's failure to initiate timely remedial action is a factor.

Full narrative available

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