NTSB Identification: LAX98LA011.
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Accident occurred Sunday, October 12, 1997 in QUINCY, CA
Probable Cause Approval Date: 09/04/1998
Aircraft: Cessna 170A, registration: N9212A
Injuries: 4 Uninjured.

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

The pilot reported that the approach, landing flare, and touchdown were normal. He further stated that during the initial ground roll, a very strong tail wheel vibration began, which 'shook the plane and overrode my rudder controls.' The pilot was unable to regain control, and the aircraft veered to the left, then ground looped in a very tight circle. Written statements submitted by the passengers were consistent with the pilot's report. An FAA airworthiness inspector examined the runway and aircraft. He reported that tail wheel scrub marks were present on the runway pavement in a high frequency wave pattern which led to the point of the ground loop. Examination of the aircraft disclosed about 1/8-inch play in the tail wheel bearings. The inspector also reported that the tail wheel was improperly shimmed. Review of the maintenance records disclosed that the tail wheel was replaced 12 days before the accident. Work orders from the repair shop (that installed the unit) noted that the tail wheel assembly was supplied by the owner. The work order noted that the bearings were replaced by the shop at the time of installation.

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

loss of directional control due to a severe tail wheel vibration, which was induced by an improperly installed and adjusted tail wheel assembly.

Full narrative available

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