Cessna 210 N7464E accident near Walsh, Colorado

Probable cause

A partial loss of engine power due to failure of the No. 2 cylinder as a result of the failure of the repair facility to properly torque the lower four nuts on the cylinder.

NTSB analysis

The airplane was in level cruise flight at 6,500 feet mean sea level when the pilot "detected a slight smoke smell." Oil pressure and oil temperature readings were normal, but he noticed the EGT (exhaust gas temperature) on one of the cylinders had dropped, followed shortly thereafter by the EGT decay of another cylinder. The pilot was forced to make an emergency landing in an open field. Recent rains had softened the ground and when the nosewheel touched down, the airplane nosed over. An FAA airworthiness inspector who examined the engine said that the cylinder hold-down studs on the lower side of the number 2 cylinder had threads, but one stud had snapped off. Further examination of the engine revealed that the lower four nuts on the number two cylinder were not properly torqued, which allowed the lower side of the cylinder to move while the upper part remained fixed. A crack developed on the right side of the cylinder and propagated along the bottom lip to the left side of the cylinder, eventually reaching the point of failure. When the annual and 100-hour inspections were done on August 21, 2009, all 6 cylinders had been removed “due to low compression” and replaced with overhauled cylinders, new pistons and rings, and new gaskets and seals. Airframe total time was 3,797.79 hours, and the time since major engine overhaul was 1,239.82 hours. The tachometer read 2960.72. At the accident site, the tachometer read 3059.41 hours.

Text from the NTSB. Open the NTSB docket for CEN10LA032 for the full record.