NTSB Identification: ANC98IA026.
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Incident occurred Wednesday, March 11, 1998 in ANCHORAGE, AK
Probable Cause Approval Date: 02/16/2001
Aircraft: Boeing 737-205, registration: N733AR
Injuries: 81 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
During parking at the gate, the airplane's rudder began a rapid rudder oscillation which shook the entire airplane. Postincident testing determined that the rudder was oscillating approximately 1.5 degrees either side of centerline, solely within the authority of the yaw damper. No corresponding cockpit rudder pedal movement occurred. Further testing revealed a loss of grease to the yaw rate gyro spin bearings, and corresponding damage to the spin and gimbal bearings. The yaw damp coupler and gyro had accumulated 24,850 hours in service.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The dynamic imbalance in the yaw rate gyro, which provided input to the yaw damper and rudder. A factor was the deteriorated grease in the gyro bearings. Full narrative available
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