NTSB Identification: LAX08LA008.
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Accident occurred Tuesday, October 09, 2007 in Alamo, NV
Probable Cause Approval Date: 09/26/2008
Aircraft: Mooney M20F, registration: N9612M
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 pilot reported that before departing for the cross-country flight, he added 1 quart of oil to the engine, for a total of 7 quarts. About an 1 hour 30 minutes into the flight, he noticed a rise in oil temperature. The pilot opened the cowl flaps and increased the mixture. This resulted in a drop in exhaust gas temperature (EGT). The oil temperature continued to rise; however, the oil pressure indicated a low reading. The pilot declared an emergency, and prepared to land on a dirt road. The pilot reported that the engine was backfiring before it suddenly stopped (froze). Once the engine quit, the airplane rolled sharply to the right. The pilot was able to correct back to level flight and landed in a sagebrush field close to a road, which resulted in substantial damage to the wings. Examination of the wreckage revealed a hole in the crankcase above and below the number 4 cylinder. An attempt was made to manually rotate the crankshaft; however, only partial rotation was possible about 8 inches in either direction. The examination also revealed no oil on the outside of the airplane or on the cowl. Investigators drained the oil out of the oil sump for a total of 0.75 to 1.25 quarts of oil. Along with the oil, portions of crankcase, lifter, piston, and connecting rod material were in the oil sump. The oil filter was opened and contained metallic debris throughout the filament and in the can. All of the cylinders exhibited internal mechanical damage, as well as thermal damage to the number 4 connecting rod journal. The number 2 piston compression ring remained in its ring land, but had broken into several pieces. Extensive oil coking signatures were noted around the circumference of the number 2 piston at the ring land, which is consistent with oil burn.

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

Failure of the number 2 cylinder piston compression ring, which resulted in oil exhaustion and a catastrophic internal engine failure.

Full narrative available

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