Flight Details
On July 16, 2012, at 0950 mountain daylight time, a Cessna 172N, registration N5204K, experienced a partial loss of engine power while in level cruise flight. The aircraft was registered to Teton Leasing, LLC, and operated by the pilot under 14 Code of Federal Regulations Part 91 for an instructional cross-country flight. Visual meteorological conditions prevailed, and a visual flight rules flight plan was filed. The flight originated from Idaho Falls Regional Airport (IDA) at 0835.
The flight instructor reported that the planned route was from IDA to Arco-Butte County Airport (AOC), then to McCarley Field Airport (U02), and back to IDA. The segment from IDA to AOC was uneventful.
Engine Failure and Forced Landing
Approximately 12 miles northwest of U02, the engine began to vibrate, and the engine revolutions dropped to about 1,900 rpm. The pilot applied carburetor heat, set the mixture to rich, and confirmed the fuel selector was in the BOTH position. The aircraft could not maintain altitude, so the flight instructor took control and decided to divert to Rockford Municipal Airport (2U4) for a landing.
Upon arrival at 2U4, the flight instructor determined the winds were calm and elected to land on runway 16. However, during the landing sequence, the altitude and airspeed were too high for a safe landing on the runway. The instructor aborted the landing and initiated a forced landing to a wheat field. During touchdown, the airplane collided with the wheat, the nose pitched down, and the aircraft came to rest inverted. The certified flight instructor and student pilot were not injured. The airplane sustained substantial damage to the wings and the tail section.
Postaccident Examination
A Federal Aviation Administration (FAA) inspector conducted a postaccident examination of the engine. The visual inspection revealed no catastrophic failures; however, a compression check showed that cylinders number two and three had no compression. Closer inspection of the number three cylinder revealed damage to the piston head and the absence of the exhaust valve. With the exhaust section removed, the inspector observed the head of the missing valve embedded into the cylinder head. The valve stem was missing and not located. Inspection of the number two cylinder revealed a large amount of metal dust and debris in the intake and exhaust ports.