NTSB Factual Report

On October 4, 2016, at 1511 central daylight time, a Cessna 172K single-engine airplane, N46377, impacted a cornfield during a forced landing following a partial loss of engine power while maneuvering near Wilmot, Wisconsin. The private pilot, who was the sole occupant, was not injured, and the airplane sustained substantial damage to the right wing. The airplane was registered to 696 Corp, Grayslake, Illinois, and operated by a private individual as a Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident and a flight plan was not filed. The flight departed the Burlington Municipal Airport (BUU), Burlington, Wisconsin, about 1445.

According to the pilot, while maneuvering after takeoff from BUU, the engine began to lose power. The pilot then switched fuel tanks, applied carburetor heat, full rich mixture, but the engine remained at reduced power. The pilot attempted to land at Westosha Airport, Wilmot, Wisconsin, however, he overshot the runway. The pilot then decided to execute a forced landing to an adjacent cornfield. During the forced landing, the right wing impacted the corn, and the airplane came to rest upright.

The accident engine was a 150-horsepower, four cylinder, Lycoming O-320-E2D engine, serial number L-22806-27A. It was examined at the facilities of Myers Aviation, Oshkosh, Wisconsin, under the supervision of the National Transportation Safety Board (NTSB) investigator and inspectors from the Federal Aviation Administration (FAA). Visual examination of engine exterior and components revealed no anomalies that would have precluded normal operation. The engine oil filter was removed and disassembled. The internal filter displayed heavy deposits of metal material. Due to the metal deposits in the oil filter, the engine was disassembled. Partial disassembly of the engine revealed the number 1 cylinder piston pin plug was destroyed and metal debris was noted in the engine oil and engine oil filter. The engine crankshaft and connecting rods displayed discoloration and heat signatures consistent with oil starvation. The number 3 and 4 connecting rod bearings were extruded and melted from the rod journals. The cylinder bores displayed corrosion and discoloration on their respective inner surfaces.

According to the engine records, the engine underwent its most recent annual inspection on October 1, 2015, at a total time of 3,160 hours, and 1,176 hours since major overhaul. At the time of the accident, the engine had accumulated 34 hours since its inspection.

NTSB Probable Cause

A failure of the No. 1 piston pin plug due to corrosion in the cylinder barrel, which resulted in oil contamination, oil starvation to the crankshaft connecting rod bearings, and a subsequent partial loss of engine power.