Cessna T206 N35442 accident near Pittsfield, Maine

Probable cause

Wear of the No. 4 cylinder exhaust camshaft lobe and roller tappet, which resulted in the failure of the tappet and the subsequent total loss of engine power.

NTSB analysis

The pilot stated that he was returning after a mission flight when he heard a "bang." The engine then lost power. He declared an emergency with air traffic control and received radar vectors to a nearby airport, but the airplane impacted a heavily wooded marsh about 3/4 mile from the runway, which resulted in serious injury to the pilot and substantial damage to the airplane. Postaccident examination revealed that the No. 4 cylinder exhaust hydraulic roller tappet was fractured and had separated. Further examination of the engine revealed that the No. 4 exhaust camshaft lobe and the corresponding roller tappet were severely worn and damaged. Additionally, the No. 4 exhaust roller tappet body ears, which supported the roller shaft and bearing, were also damaged, and one of the ears had fractured in fatigue. Metallurgical examination showed that the engine components conformed to the manufacturer's specifications. It is likely that the severe wear between the roller and camshaft led to nonstandard loading conditions, the fatigue failure of the roller tappet body ear, the subsequent liberation of the roller and its components, and the total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA18LA228 for the full record.