ERA23LA141 · Cessna 172M

The flight instructor was conducting an instructional flight when the engine began to make a “knocking” noise, followed by a total loss of oil pressure and subsequent loss of engine power. The instructor reported they were unable to return to the airport and made a forced landing to a marsh area. The nose wheel of the airplane dug into the soft/wet terrain and the airplane slowly flipped over, resulting in substantial damage to an engine mount. Postaccident examination of the airplane revealed there were no major oil streaks on the lower engine cowling and fuselage; however, there was some dark oily residue noted on the right underbelly of the airplane that appeared to have been there for an extended period of time. The engine did not seize and crankshaft rotated freely when the propeller was manually rotated. Examination of the engine’s oil system revealed no obvious mechanical failures; however, damage signatures were observed that were consistent with a lack of lubrication. The instructor said they departed for the flight with 6 quarts of oil; however, about one quart of dark oil was drained from the engine following the accident. Pieces of metal were found throughout the oil system consistent with high heat, friction, and metal-to-metal contact within the engine. A review of the engine maintenance records revealed the engine was 55 hours past its last 100-hr inspection. Based on the instructor’s report that the engine was “knocking,” followed by a loss of oil pressure and a power loss, and evidence of high heat, friction, and metal-to-metal contact within the engine with no sign of leaks in the oil system, the engine was likely being operated with an inadequate oil level at the time of the power loss. Though the engine did not fully seize, the damage found throughout the engine most likely contributed to a loss of engine power.

Verbatim NTSB analysis and probable cause from the NTSB dataset