Beech V35B N246JT accident near Long View, North Carolina

Probable cause

The improper installation of the lower rear crankshaft counterweight snap rings by unknown maintenance personnel, which resulted in the separation of the counterweight and a subsequent total loss of engine power during initial climb.

NTSB analysis

The pilot reported that, during initial climb, he heard a big "bang," which was followed by a total loss of engine power. He subsequently performed a forced landing straight ahead into trees. Teardown examination of the engine revealed that the lower rear crankshaft counterweight had separated. During a subsequent examination, all four snap rings from the lower rear crankshaft counterweight were found loose in the engine, and one of the rings was found broken in half. Three of the lower rear counterweight retaining plates were found, but the fourth retaining plate was not recovered. Two snap rings that were still in place on the upper rear crankshaft counterweight were examined. The examination revealed that the width between the snap ring ears on one of the snap rings did not meet the manufacturer-prescribed width, indicating that the snap ring was not properly seated. After that snap ring was removed and its groove was cleaned of deposits with a wire brush, it seated properly when reinstalled.

A review of maintenance records revealed that, about 16 years before the accident, the engine had been rebuilt and had accumulated about 1,600 hours since it was rebuilt and that, about 8 years before the accident, a top overhaul was performed on the engine. The crankshaft was inspected about 6 months after the factory rebuild in accordance with an airworthiness directive (AD); however, there likely would have been little to no deposits in the crankshaft so soon after the factory rebuild. Before the issuance of the AD, the engine manufacturer had issued a mandatory service bulletin, which included a warning that the "failure to properly install counterweight retaining plates and snap rings may result in engine damage and possible failure." It is likely that the lower rear crankshaft counterweight snap rings were not properly installed; however, it could not be determined when or by whom they were improperly installed.

Text from the NTSB. Open the NTSB docket for ERA15LA092 for the full record.