Amateur-built RV7 - UNDESIGNAT N513BW accident near Belfair, Washington

Probable cause

A total loss of engine power during cruise flight due to the fatigue failure of the engine crankshaft. Contributing to the accident was the unapproved repair and improper inspection of the engine crankshaft.

NTSB analysis

The pilot reported that the airplane was at 1,500 ft mean sea level as he was returning to the departure airport when the engine "abruptly quit." When all attempts to restart the engine failed, the pilot chose to land on a gravelly split. During the landing roll, the airplane's small tires sunk into the gravel, which resulted in the airplane nosing over.

A postaccident examination of the engine revealed that the crankshaft had fractured adjacent to the aft radius of the No. 3 rod journal. Examination of the crankshaft revealed that it failed due to fatigue cracking that had initiated at locations on either side of a preexisting longitudinal crack. The radius also contained several circumferential cracks, including ones in the region corresponding to the relative location of the fatigue origins of the fracture. Examination also revealed that the No. 3 rod journal had been chromium-plated to regain lost material; however, according to the engine manufacturer, chromium plating on bearing journals was not an approved repair. Although the fatigue did not initiate in the plating, it did start near the edge of the replating in an area likely reworked (ground) following the unapproved plating. The multiple circumferential cracks noted in the radius likely resulted from the repair grinding and may have contributed to the fatigue initiation. A review of the engine logbooks revealed that the engine had been overhauled and subsequently inspected by the "magnaflux method" three times in a 14-month period about 15 years before the accident, during which the extensive cracking would have been present, indicating that the magnaflux inspections of the crankshaft were not effectively performed.

Text from the NTSB. Open the NTSB docket for WPR15LA101 for the full record.