Accident Description
The airplane was seen flying erratically, in a rapid descent, with smoke coming from the engine compartment and flames coming from the airplane's right side. Subsequently, the airplane crashed/landed and burned.
Investigation Findings
An investigation revealed that the #1 cylinder had separated from the engine. Examination of the #1 cylinder showed that the upper crankcase thru-bolt at the 10 o'clock position had failed in fatigue below the cylinder deck surface. The lower thru-bolt at the cylinder pad's 8 o'clock position was intact; however, the nut was missing and the threads were battered and polished. The cylinder had six deck studs in addition to the thru-bolts. The studs at the 11 and 1 o'clock positions were missing; the studs at the 5 and 7 o'clock positions failed in fatigue; and the studs at the 2 and 4 o'clock positions were fractured with the fractured ends battered. Additionally, a silicon sealant (RTV) had been used on the thru-bolt threads, though not recommended by the manufacturer. The remaining thru-bolts were examined for tightness using a torque wrench; all were found undertorqued.
Maintenance History
During a top overhaul of the engine, about 85 flight hours before the accident, all of the cylinders had been removed and reinstalled.