Narrative:

We decided to fly back before the engine cooled too much because it was really cold out. We preflighted the aircraft and departed at XA03PM. 20 minutes into the flight; we noticed the oil pressure was dropping. Center was providing us with VFR flight following at 5;500 ft. I told them that we needed a heading for ZZZ. They gave us a heading of 360 degrees and said we were 15 mile south of the airport. Center wanted to know if that was to be our destination and why we were changing our destination. I told them that we were going to have engine problems due to a loss in oil pressure and that it's our destination. During the next 10 minutes; we kept communicating with center on the position of the airport. After the aforementioned 10 minutes; the engine then quit and we notified center that we found a field to land in because we were not going to make it to the airport. We completed the checklist and successfully landed the airplane in the farmer's field next to his house. We called center and told them we were on the ground safe and that there was no damage to the aircraft or property. We got out of the airplane and noticed the belly was covered with oil. We then secured the airplane. I am not sure what has caused the oil leak; but I will find out soon. I do know the engine was past tbo and that it should be mandatory for all aircraft engines to be overhauled at the specified times. There is a reason why the manufacturers put time limits on motors and that it should be adhered to. Callback conversation with reporter revealed the following information: the engine has not been torn down yet so the cause of the oil pressure loss is undetermined. The loss of oil pressure caused rotating parts to rupture the engine case so the cause of the pressure loss may never be determined. Reporter states although the engine was over the manufacturers recommended tbo; the engine had been well maintained over the years. Pistons and cylinders had been replaced when necessary.

Related reports:

Google
 

Original NASA ASRS Text

Title: C172 pilot reports oil pressure dropping and eventual engine failure. Reporter makes safe landing in farmers field without damaging aircraft.

Narrative: We decided to fly back before the engine cooled too much because it was really cold out. We preflighted the aircraft and departed at XA03PM. 20 minutes into the flight; we noticed the oil pressure was dropping. Center was providing us with VFR flight following at 5;500 ft. I told them that we needed a heading for ZZZ. They gave us a heading of 360 degrees and said we were 15 mile south of the airport. Center wanted to know if that was to be our destination and why we were changing our destination. I told them that we were going to have engine problems due to a loss in oil pressure and that it's our destination. During the next 10 minutes; we kept communicating with Center on the position of the airport. After the aforementioned 10 minutes; the engine then quit and we notified Center that we found a field to land in because we were not going to make it to the airport. We completed the checklist and successfully landed the airplane in the farmer's field next to his house. We called Center and told them we were on the ground safe and that there was no damage to the aircraft or property. We got out of the airplane and noticed the belly was covered with oil. We then secured the airplane. I am not sure what has caused the oil leak; but I will find out soon. I do know the engine was past TBO and that it should be mandatory for ALL aircraft engines to be overhauled at the specified times. There is a reason why the manufacturers put time limits on motors and that it should be adhered to. Callback conversation with reporter revealed the following information: The engine has not been torn down yet so the cause of the oil pressure loss is undetermined. The loss of oil pressure caused rotating parts to rupture the engine case so the cause of the pressure loss may never be determined. Reporter states although the engine was over the manufacturers recommended TBO; the engine had been well maintained over the years. Pistons and cylinders had been replaced when necessary.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.