Beech 23 N7941L accident near Cleburne, Texas

Probable cause

The total loss of engine power due to metal fatigue failure of the No. 1 cylinder wall.

NTSB analysis

The private pilot departed on a local flight and had flown for “several” minutes when the oil pressure began decreasing. The pilot elected to return to the departure airport. As he continued on his return, the engine started “shaking” and subsequently stopped. He performed a forced landing on a curving gravel road and subsequently departed the road and impacted bushes and a tree, resulting in substantial damage to the airplane’s right wing.

A postimpact examination of the engine revealed the No. 1 cylinder head was separated and the piston exposed. Further examination revealed fatigue cracking through the cylinder wall. The failure initiation was a through-wall crack located on the exhaust side of the cylinder. A review of the airplane logbook revealed debris was found under the oil pressure relief valve seat 4 years prior to the accident, which “caused the oil pressure gage to read zero.” Further review showed that the oil pressure relief valve had been removed, cleaned, and reinstalled 8 months before the accident and that, 3 weeks prior to the accident, the oil pressure relief valve seat was honed, and a new plunger was installed. It is likely the separation of the No. 1 cylinder head was a result of metal fatigue, which in turn, resulted in the complete failure of the engine.

Text from the NTSB. Open the NTSB docket for CEN20LA211 for the full record.