Event Description
The airplane was in cruise flight at 3,500 feet near the Potomac River when it experienced a partial loss of engine power. The pilot checked the magnetos and engine controls, and noted a slight restoration of power after adjusting the mixture. Within three minutes, the engine lost all power. The pilot turned away from the river and executed a forced landing to a farm pasture.
Examination Findings
Post-accident examination of the airplane revealed that the number 3 cylinder was loose on the crankcase. The number 3 intake tube was not installed and was resting in the bottom of the engine compartment. The number 3 exhaust riser was found separated at the flange; the flange was loose, with two nuts not tight, and one nut missing a washer or lock washer. Further inspection showed that two case studs and two through studs along the bottom of the number 3 cylinder were broken off. The cylinder was removed and visually examined; the cylinder skirt exhibited chafing and scratching, with corresponding scratching on the cylinder case pad material. Examination of the fractured cylinder studs revealed fracture surfaces with features consistent with fatigue.
Maintenance History
The engine had been overhauled 14 years and 917 flight hours prior to the accident. No cylinders had been removed during that time. The engine manufacturer recommended overhaul every 2,000 hours or 12 years, whichever occurred first.
Probable Cause
Not specified in the source.