SELMA, CA, USA
N5516Q
MOONEY M20E
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.
Source: NTSB Aviation Accident Database
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