Beech 36 N2021T accident near Fredericksburg, Texas

Probable cause

The loss of engine power due to fatigue failure of the crankshaft.

NTSB analysis

The accident pilot was in cruise flight in a single-engine airplane when he declared "mayday" on the radio, stating the airplane's engine was on fire. The accident airplane impacted a field, crossed a road, and came to rest upright. A postcrash fire consumed the majority of the airframe.

The airplane was equipped with a turbo-charged reciprocating engine and propeller that had been converted under a Supplemental Type Certificate (STC). The engine had accumulated 412.2 hours between the last overhaul and the last annual inspection. The last inspection was about three months before the accident.

An examination of the engine revealed fire damage and limited rotation. Disassembly of the engine revealed a broken camshaft and crankshaft. Metallurgical examination of the crankshaft revealed crack arrest marks in the crankshaft, consistent with fatigue, which initiated in the fillet radius at the forward end of the number 6 connecting rod journal. Multiple crack origins and prominent crack arrest lines were consistent with a relatively high stress associated with crack initiation. However, a reason for the high stress or fatigue initiation could not be determined based on the limited airplane records and the damage to the airplane.

Text from the NTSB. Open the NTSB docket for CEN19LA055 for the full record.