FAA Expected To Formalize Compliance With Mandatory Service Bulletin SB 632A

The owners of thousands of aircraft equipped with Lycoming engines have been notified of Lycoming Mandatory Service Bulletin 632A titled “Identification of Connecting Rods with Non-Conforming Small End Bushings.”

According to Michael Busch, CEO of Savvy Aviation, the bulletin is intended to address a problem with small-end connecting rod bushings (part number LW-13923) that were used shipped by Lycoming to overhaul shops and mechanics between November 2015 and November 2016. There apparently was a quality control problem with the bushings, and some did not have the correct outside diameter to conform with engine specifications.

In a small number of cases, the bushings appear to be migrating out of the connecting rod while in service, which has led to the SB.

At the very least, the SB 632A will affect well over a thousand new and Lycoming-Factory-Rebuilt engines. What is not known is how many engines have been overhauled or repaired in the field during the time when the bushings were being used, and neither Lycoming or the FAA has been willing to say what that number is.

To comply with the SB 632A, any engine that may have the non-conforming bushing must have all cylinders removed within the next 10 hours of operation, and a special tool must be used to determine if the bushing fits properly. Lycoming estimates that there will be a 20 percent failure rate, meaning one in every five connecting rods will have to be replaced. Busch warns that there is a history of catastrophic engine failures after all cylinders have been removed in the field. They also say that the majority of A & P mechanics do not have the expertise to conduct the inspections.

Lycoming has more recently issued a revision of the Service Bulletin, but Busch still believes that the likely AD will be "painful" for may Lycoming owners.

(Image provided with Savvy Aviation newsletter)

FMI: Original Report, SB 632A