Cessna 172M N12504 accident near South Wayne, Wisconsin

Probable cause

Internal engine component failures, which resulted from oil starvation due to debris in the oil system.

NTSB analysis

The pilot reported that, after about 2 hours 20 minutes of uneventful flight and while cruising at 4,500 ft mean sea level, the engine rpm decreased. He applied carburetor heat, and, about 2 minutes later, the engine rpm decreased to about 1,500, the oil pressure dropped to 0, and the propeller stopped. The oil temperature indicator in the cockpit was in the normal range. The pilot chose to execute a forced landing in a soybean field since an airport was not within glide distance. Upon touchdown in the field, the airplane flipped over and then came to rest inverted.

Examination of the airplane wreckage revealed that a sufficient quantity of oil (about 5 quarts) was present in the engine and that the lubrication system was intact and appeared to be in compliance with applicable airworthiness directives. However, two pieces of foreign plasticlike material, which were about 1/4 inch by 3/8 inch and 1/4 inch by 5/16 inch, respectively, were found lodged in the oil sump screen. The debris likely blocked oil distribution to the engine, which resulted in oil starvation and the subsequent connecting rod failure. It could not be determined how the debris got into the oil system; the exact source of the debris also could not be determined.

Text from the NTSB. Open the NTSB docket for CEN12LA508 for the full record.