Beech A36TC N2WZ accident near Erwin, North Carolina

Probable cause

The partial loss of engine power shortly after takeoff due to fatigue-fractured exhaust valve springs. Contributing to the accident was the mechanic’s decision to install exhaust valve springs with an unknown service history in the engine’s No. 4 cylinder.

NTSB analysis

After what he described as an uneventful engine run-up, the pilot took off from the 5,000-foot-long runway. The pilot stated that when the airplane reached an altitude of about 50 feet, he retracted the landing gear; the engine lost partial power. The airplane yawed to the left and touched down again, impacting a thicket. According to a witness who observed the takeoff, the engine power never decreased until the engine stopped suddenly upon impacting the ground.

Postaccident examination of the engine revealed that the No. 4 cylinder exhaust valve springs had fractured in fatigue. Detailed examination of the springs showed that the fatigue cracking likely originated from one or more of the iron oxide (rust) pits present on the surface of the springs. The springs had been installed in the engine about 1 year before the accident flight. According to the mechanic who installed the springs, he had retrieved them from a similar engine’s cylinder that was removed from another airplane; there was no documentation of the springs’ service history or serviceability.

Text from the NTSB. Open the NTSB docket for ERA12LA336 for the full record.