NTSB Identification: LAX86LA059.
The docket is stored on NTSB microfiche number 30130.
Accident occurred Sunday, December 08, 1985 in SELMA, CA
Aircraft: MOONEY M20E, registration: N5516Q
Injuries: 1 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.

DURING CRUISE ON A VFR X-COUNTRY FLT, THE PLT STATED THAT THE ENG BECAME ROUGH WITH MODERATE VIBRATION LEVELS. AFTER SHUTTING DOWN THE ENG, THE PLT MADE A FORCED LANDING IN A FLD, COLLIDED WITH GND OBSTRUCTIONS & COLLAPSED ALL 3 LANDING GEAR. EXAMINATION OF THE ENG REVEALED THAT THE NUTS ON THE HOLD DOWN STUDS FOR THE #3 CYLINDER HAD BACKED OFF WHICH OVERSTRESSED THE REMAINING NUTS & CAUSED THEM TO FAIL. THE #3 CYLINDER WAS FOUND SEPARATED FROM THE CASE. ACCORDING TO THE IA WHO EXAMINED THE ENG, THE NUTS ON THE NUMBERS 3 & 4 CYLINDERS WERE UNDERTORQUED DURING A PRIOR MAINTENANCE PERIOD. THE IMPROPER TORQUE LEVELS ALLOWED SOME OF THE NUTS TO LOOSEN & EVENTUALLY BACK OFF, PRECIPITATING THE SEQUENCE OF EVENT.

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

ENGINE ASSEMBLY,CYLINDER..LOOSE

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

ENGINE ASSEMBLY,CYLINDER..UNDERTORQUED

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

MAINTENANCE,MAJOR REPAIR..IMPROPER..FBO PERSONNEL


Contributing Factors

TERRAIN CONDITION..HIGH VEGETATION


Contributing Factors

TERRAIN CONDITION..NONE SUITABLE

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