Piper PA 28RT-201T N2175K accident near Dawson Springs, Kentucky

Probable cause

The fatigue failure of a crankshaft counterweight, which resulted in a total loss of engine power during cruise flight.

NTSB analysis

The private pilot of the single-engine airplane was conducting an instrument flight rules flight. The pilot reported that, when the airplane was in cruise flight at 7,000 ft mean sea level, he heard two loud bangs, followed by a total loss of engine power, pieces of the engine exiting the cowling, and oil covering the windscreen. The pilot attempted to divert to another airport; however, after descending through a low cloud layer, he could not visually locate the turf runway, so he performed a forced landing to a field.

Teardown examination of the engine revealed that a rear crankshaft counterweight had separated and that the adjacent (No. 2) connecting rod had separated at the connecting rod bolts. Metallurgical examination of the counterweight revealed fatigue cracking that had originated at the counterweight aft blade surface near a bushing hole, consistent with a loose bushing moving in the hole over a prolonged period of time.

A review of maintenance records revealed that the engine had been operated for about 1,130 hours since its last overhaul, which was completed about 19 years before the accident; the engine was 7 years beyond the 12-year recommended time between overhaul (TBO). The engine manufacturer had previously issued a service bulletin, which included a warning that the improper installation of bushings during overhaul could cause engine failure. Although the failure mode evidence was consistent with a loose bushing, it was not likely due to improper installation given that the engine had operated for almost 7 years beyond its 12-year recommended TBO. If the engine had been overhauled at the recommended time, all of the bushings would have been required to be replaced with new bushings.

Text from the NTSB. Open the NTSB docket for ERA15LA377 for the full record.