Accident Narrative
During cruise flight at full throttle, with the engine operating between 2,700 and 2,800 rpm (maximum 3,200 rpm), the engine began to run rough. Subsequently, engine rpm and oil pressure decreased. The flight instructor performed emergency procedures, but they did not restore engine power. A forced landing was made in a wet field. During the landing, the nose gear collapsed and the airplane nosed over, coming to rest inverted. This flight was the instructor's first time operating this make and model of aircraft.
Preflight and Maintenance History
Before takeoff, the left magneto drop was measured and found to exceed the allowable maximum of 125 rpm. The last annual inspection was conducted in April 1997 at a tachometer reading of 1,956.59 hours. At the time of the accident, the tachometer read 1,995.61 hours.
Engine Teardown Findings
A teardown of the engine revealed a hole in the number 6 cylinder piston. The rod cap and bolts for the number 3 cylinder connecting rod had separated, and the components of the number 3 connecting rod exhibited overload features. The number 6 cylinder piston showed physical evidence of detonation or preignition.