Piper PA-28R-200 N300KR accident near Watertown, Wisconsin

Probable cause

The separation of the number 2 connecting rod from the crankshaft for reasons that could not be determined during postaccident metallurgical examination, which ultimately resulted in a total loss of engine power.

NTSB analysis

The pilots were about 5 miles from the destination airport when they heard a "loud bang" and engine oil immediately covered the front windshield. The engine continued to produce partial power until the airplane was in the airport traffic pattern, and then it lost total power. Due to a complete lack of forward visibility and another airplane in the runway run-up area, the flight instructor elected to make a forced landing on a roadway bordering the east side of the airport. The airplane struck a car and a pole before coming to a stop.

A postaccident examination of the engine revealed that the number 2 connecting rod had separated from the crankshaft. The connecting rod failed about mid-length, with the upper portion remaining attached to the piston. The lower portion of the connecting rod was not recovered. The upper portion of the connecting rod and a recovered section of the rod cap both failed as a result of overstress bending. Neither component appeared discolored, which suggests there was an adequate engine oil supply before the failure. The number 1 and 3 connecting rods remained attached to the crankshaft; the number 4 connecting rod had separated from the crankshaft. The number 1, 3, and 4 connecting rods were discolored, consistent with continued operation with an insufficient supply of engine oil. Deformation of the lower end of the number 4 connecting rod was consistent with secondary mechanical damage; however, the rod appeared otherwise undeformed.

A lack of evidence of oil starvation and the preponderance of crankcase damage in the area of the number 2 cylinder suggests that the engine failure was initiated by the separation of the number 2 connecting rod from the crankshaft. Metallurgical examination of the number 2 cylinder assembly and related components did not identify the initiating cause of this connecting rod separation. The total loss of engine power occurred upon separation of the number 4 connecting rod, which was precipitated by the prior loss of engine oil and secondary to the initial failure.

Text from the NTSB. Open the NTSB docket for CEN12FA025 for the full record.