FAA concerned about converted Continental engine crankshafts

An airworthiness concern sheet issued July 8 applies to Continental Aerospace Technologies O-470-K, -L, -M, -R, -S, and -U engines of all serial numbers that were converted to O-470-50 engines by supplemental type certificate SE4985NM.

The manufacturer “was made aware of an engine that lost power, while in flight, with the pilot smelling smoke in the cockpit, resulting in the pilot conducting a forced landing with no injuries. The investigation found that the modified Continental O-470 engine’s crankshaft was fractured between the #5 and #6 cylinders,” the ACS says. The engine had been converted under “STC SE4985NM, to increase the engine displacement, and STC SE10233SC, to install a supercharger.”

The Airmelt crankshaft, which was ground down and inspected for reuse, was of a type “not designed to be used on the bigger bore engines,” raising concern that Airmelt crankshafts “are being improperly used in these converted O-470 engine models,” and prompting the FAA to act “to better understand the overall impact on the flying public,” the ACS says.

The ACS asks operators of the listed engines to email the FAA with answers to the following questions:

“1) Have you installed STC SE4985NM to convert your O-470-K, -L, -M, -R, -S & -U engine into an O-470-50 by increasing the engine displacement?

2) If the answer to question one was ‘Yes,’ have you also installed STC SE10233SC to install a Belt-Driven Vortech V-1S supercharger assembly on the same Continental engine (either before or after STC SE4985NM was installed)? Or any other engine-related STC’s in addition to STC SE4985NM?

3) If you have an engine with either STC SE4985NM, SE10233SC or both installed, please confirm whether your crankshaft was manufactured using the Airmelt process or the Vacuum Arc Remelt (VAR) forging process (please refer to CSB96-8 for guidance on how to identify your type of crankshaft). If you do not know which process was used for your crankshaft and are unable to determine it, please respond to this question with ‘Unknown.’”

AOPA believes the ACS process is an effective way for the FAA to interact with the general aviation community on matters of flight safety before taking potentially unnecessary regulatory action, and we encourage operators to provide the information sought. The resolution of airworthiness concerns addressed by evaluating data collected through this process could range from no further action being taken to the issuance of an airworthiness directive.