Incident Overview
The airplane was in level flight at approximately 3,000 feet with the engine operating at 2,350 rpm when the student pilot noted an abnormal increase in engine noise. Subsequently, the oil pressure dropped and smoke began emanating from the engine. The student pilot reduced engine power to idle and attempted to land in a field, but overshot the intended landing area and struck trees.
Post-Flight Examination
A post-flight examination of the engine revealed seven quarts of oil on the dipstick, with no evidence of broken or loose oil lines or the oil filter. A hole was found in the crankcase in the vicinity of the #2 cylinder.
Engine Teardown Findings
An engine teardown disclosed that the #2 connecting rod had separated from the crankshaft and had outwardly bent the cylinder skirt. The connecting rod that contacted the crankshaft journal exhibited lateral scarring, heat signature, and peening. The piston, via the connecting rod, had moved the length of the cylinder barrel, with the stroke limited by the destruction of the cylinder skirt. The #2 crankshaft journal displayed characteristics identical to those on the end of the connecting rod.
The #1 cylinder connecting rod was separated from the piston and bent approximately 10 degrees at the base of the pin hole, with the piston pin still in place. The top of the connecting rod showed peen marks, as did the bottom interior of the piston. The piston could not be moved from the top of the cylinder. The connecting rod was loose on the journal, with one hold-down nut missing. The opposite hold-down bolt and nut were tight. The connecting rod exhibited rotational scratching without heat signature.
Three of four connecting rod hold-down nuts were recovered. The lipped surfaces of two nuts displayed no rotational scratch marks associated with contacting other metal surfaces; the third nut had such rotational scarring.
Engine Service History
The engine had accumulated 6,036 hours of total operation and 456 hours since its last overhaul.