NTSB Identification: MIA97LA123.
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Accident occurred Tuesday, April 08, 1997 in SMITHFIELD, NC
Probable Cause Approval Date: 01/07/1998
Aircraft: Cumberland SKYBOLT, registration: N4TZ
Injuries: 2 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 engine failed and seized as the flight approached the airport for landing. During a forced landing in a field the aircraft nosed over. Post crash examination of the engine showed a counterweight retaining clip, washer, and pivot pin had separated allowing the counterweight to move around on the remaining pivot pin. The counterweight struck the No. 5 piston connecting rod causing it to fail and seize the engine. The counterweight retaining washer was found to have been ground and to not meet the manufacturers specified dimensions. Two pieces of the washer had separated. The engine had been taken by the owner to a community college aircraft maintenance school for overhaul. The engine was returned and installed on the aircraft 83 flight hours before failure. No logbook records were found to show the engine had been overhauled. Representatives of the aircraft maintenance school stated the work performed on the engine was a repair not an overhaul and that the original counterweight retaining washers and clips had been reused.

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

Installation by a student mechanic of a counterweight retaining washer that did not meet engine manufacturers specifications resulting in partial separation of the counterweight, failure of the No.5 connecting rod adjacent to the counterweight, and seizure of the engine. Contributing to the accident was improper supervision of the student mechanic by aviation school personnel.

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