NTSB Identification: LAX91LA157.
The docket is stored on NTSB microfiche number 44132.
Accident occurred Thursday, April 04, 1991 in STOCKTON, CA
Probable Cause Approval Date: 05/03/1993
Aircraft: CESSNA 172N, registration: N733MQ
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 CERTIFICATED COMMERCIAL PILOT/CERTIFIED FLIGHT INSTRUCTOR AND A CERTIFICATED PRIVATE PILOT/INSTRUMENT STUDENT WERE IN A HOLDING PATTERN, IN VFR CONDITIONS, WHILE ON AN INSTRUMENT TRAINING FLIGHT WHEN THE ENGINE QUIT. THE CFI MADE A FORCED LANDING IN AN OPEN FIELD. DURING THE LANDING ROLL, THE AIRPLANE ENCOUNTERED SOFT TERRAIN AND NOSED OVER. EXAMINATION OF THE ENGINE REVEALED THAT THE MAGNETO ASSEMBLY FELL OFF THE ENGINE. AN IMPROPER GASKET WAS INSTALLED UNDER THE MAGNETO HOUSING THAT PREVENTED THE MAGNETO FROM BEING PROPERLY TIGHTENED TO THE REQUIRED TORQUE SETTING. GASKET MATERIAL UNDER THE NUT PROVIDED A CUSHION AFFECT THAT ALLOWED THE NUT TO VIBRATE LOOSE.

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

THE INSTALLATION BY MAINTENANCE PERSONNEL OF AN INCORRECT GASKET THAT RESULTED IN THE LOSS OF THE ENGINE MAGNETO.

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