Failure Analysis of a Reworked Aircraft Engine Cylinder

Aircraft engine cylinder failures are flight safety critical. In this case, the No. 6 cylinder from a 6-cylinder engine had a complete fracture around the circumference of the cylinder head, which allowed the aluminum cylinder head to separate from the engine. The cylinder rework involved mounting a used threaded cylinder head to a new threaded steel cylinder barrel. The new steel cylinder barrel exhibited defective truncated threads with sharp corners and nonuniform shot peening. The steel cylinder barrel thread anomalies led to fatigue cracking in the mating softer aluminum cylinder head threads. The subject cylinder head also had fatigue cracks present that were not detected during the rework process.

The reworked cylinder used a cylinder head with an unknown service history mated to a new steel cylinder barrel. The new steel cylinder barrel had been defectively manufactured, which resulted in damage to the mating cylinder head threads, thru-wall fatigue cracking in the cylinder head threads and cylinder separation.