The FAA has issued a notice of proposed rulemaking (NPRM) for specific Superior Air Parts (SAP) cylinder assemblies that may be installed in up to 8,000 aircraft here in the U.S. The engines in question are Teledyne Continental Motors (TCM) IO-520, TSIO-520 and IO-550 models. Specific SAP cylinders (identified by part number) installed in those engines may be prone to cracks near the exhaust valve, potentially leading to separation of the cylinder head, structural damage, immediate engine failure, and fire in the engine compartment. The proposed airworthiness directive would require initial and repetitive compression checks for those cylinders that also have acquired more than 750 hours time in service. Some 24 failures have so far been reported to the FAA, half of them by SAP. All of those failures occurred in cylinders with more than 823 hours time since new. The FAA is seeking comments before June 11. Find the additional information you need, here.