Would Affect All 520- And 550-Series Engines

Over the weekend, Continental Motors issued Mandatory Service Bulletin MSB05-8B affecting all 520- and 550-series engines (plus a few IO-470s). Normally, Part 91 operators are not required to comply with manufacturer’s service bulletins. However, when Continental issues a Mandatory Service Bulletin, it means that they have asked the FAA to issue an Airworthiness Directive (AD) to make compliance compulsory. That’s the case with MSB05-8B.

In 2005, Continental issued Service bulletin SB05-8 announcing the release of an improved camshaft gear (part number 656818) to replace earlier camshaft gears (part numbers 631845, 655430, 655516, and 656031). The new-style gear was thicker than the older-style ones. SB05-8 recommended (but did not require) that the new-style camshaft gear be incorporated at the next engine overhaul or whenever replacement of the camshaft gear was necessary.

Replacing the camshaft gear can only be accomplished if the engine is completely disassembled (crankcase split), so the only reasonable time to perform this replacement is when the engine is being overhauled or the case is split for some other reason (e.g., a post-prop-strike inspection). It also turned out that for Permold-case engines (with front-mounted alternators and rear-mounted oil coolers), the new thicker camshaft gear had an interference problem with the crankcase, so using the new gear required machining the crankcase to eliminate the interference problem.

For many years, Continental’s official recommendation has been that their engines should be overhauled at some recommended number of hours (TBO) or after 12 years in service, whichever comes first. This is only a recommendation, not a regulatory requirement, so many owners run these engines past TBO and almost nobody pays any attention to the 12-year calendar-time recommendation.

On the 12-year anniversary of SB05-8, Continental Motors has “promoted” its service bulletin to “mandatory” status, and asked the FAA to issue an AD to make it compulsory.

Michael D. Busch, CEO of Savvy Aviation says why Continental did this is not clear, because there does not appear to have been any significant numbers of accidents or incidents involving failures of the old-style camshaft gears, and there is no mention of any such failures in MSB05-8B. "Savvy manages many hundreds of aircraft with the affected gears, and in the eight years we’ve been in business we have not encountered a single camshaft gear failure," Busch said in an email to ANN. "One conjecture is that Continental’s legal department wants to get all the older-style gears out of the system for liability reasons. Another more cynical school of thought holds that issuance of such an AD would create a big financial windfall for the company. (Personally, I’m more inclined to blame the lawyers than the bean counters.)

"Now here’s the rub: MSB05-8B calls for compliance (i.e., replacing the gear) 'within the next 100 hours of operation, at the next engine overhaul (not to exceed 12 years engine time in service), or whenever the camshaft gear is accessible, whichever occurs first.' If the FAA were to do what Continental is asking, any engine built, rebuilt or overhauled prior to 2005 would have to be torn down immediately, and any newer engine would have to be torn down within 100 hours unless it can be shown that the new-style thicker gear is already installed.

"My best guess is that the FAA may not buy into the 100-hour compliance requirement, but very well might go with the 12-year requirement. But that’s only a guess. Another school of thought is that the FAA may not have an appetite to take on such an expensive and controversial AD under the anti-regulation climate of the current Administration.

"For now, all we can do is wait for the other shoe to drop and see what the FAA’s Notice of Proposed Rulemaking (NPRM) says," Busch said. "I urge every Continental owner whose engine(s) might be affected to keep a close eye out for the NPRM and reply to the rulemaking docket during the public comment period (which is usually 30 days). Unless the FAA can make a compelling case for an unsafe condition (and I sure haven't seen one), we should fight this AD tooth and nail.

"Maybe we’ll get lucky and the FAA will decline to issue the AD that Continental is asking for. Or maybe the FAA will issue an AD that calls for camshaft gear replacement only at the next overhaul or teardown (with no 12-year or 100-hour limit). Otherwise, this could get extremely expensive for a lot of aircraft owners."

(Image from file)

FMI: www.savvyaviation.com