Continental Motors released Mandatory Service Bulletin MSB05-8B in late March. This bulletin addresses replacement of the camshaft gear in certain IO-520 and -550 engines installed on Beechcraft, and IO-470, -520 and -550 engines on other airplanes.
MSB05-8B is an update to a 2005 Continental Service Bulletin, SB05-8. According to Continental, the 2005 guidance “was written to identify not only the availability of [a] new [camshaft gear] part (P/N 65818), but also provided a required Permold crankcase modification to eliminate interference with the new thicker camshaft gear. Service Bulletin SB05-8 and revision SB05-8A recommended the new camshaft gear (P/N 656818) be incorporated at the next engine overhaul or whenever replacement of the camshaft gear was required….” The new Bulletin issued in March 2017 “promotes the Service Bulletin (Category 3) to a Mandatory Service Bulletin (Category 1).”
The MSB calls for replacing the camshaft gear of affected engines within 100 hours of operation after the March 29, 2017 effective date of the Bulletin, at the next engine overhaul (not to exceed 12 years in service), or whenever he camshaft gear is accessible, whichever occurs first. In ABS-type airplanes, this affects IO-520B, -BA, -BB, -C, -CB, and –L engines, all TSIO-520 engines, and IO-550B, -C and –R engines. Presumably all new and Continental factory-rebuilt (“remanufactured”) engines produced since some time in 2005 already have the new camshaft gear installed and no action is required by this MSB. Pre-2005 engines that have not been overhauled or have had field overhauls since 2005 may or may not have the old camshaft gear installed—parts numbers 631845, 655430, 655516 and 656031 are called out for replacement under this new MSB. Check your engine logbooks or contact the overhauler/installer to confirm the camshaft gear part number installed on your engine(s).
There is concern among many ABS members for five reasons:
1. Continental Motors has followed its standard practice of requesting the FAA issue an Airworthiness Directive to make the guidance a required action for all owners.
2. The MSB incorporates Continental’s 12-year Time Between Overhauls (TBO) recommendation as a firm requirement.
3. The MSB calls for a complete “engine overhaul,” not simply engine reassembly, to return the engine to service after replacing the camshaft gear.
4. Raising the status of this bulletin to “Mandatory” indeed does make it required for aircraft registered in many countries outside the United States, and for commercial operators who have written compliance with MSBs into their operating specifications.
5. The cost/benefit analysis of mandatory replacement has not yet made or has not been made public; the very limited number of known camshaft gear failures does not appear to warrant the historic risks of overhauling large numbers of engines in a short period of time, especially for Permold engines that require a crankcase modification in order to replace the camshaft gear.
ABS Air Safety Foundation was in touch with AOPA when the FAA issued an Airworthiness Concern Sheet last December. An ACS indicates the FAA is looking at an issue but has not yet decided if it will act further. It is designed for type representatives (like ABS) to provide input. The ACS notes only three cases of camshaft gear failure, all involving P/N 655516. Camshaft gear P/N 655516 was manufactured from 1999 to 2002. Our opinion at the time was that the scope of failures is so very limited that no AD action would be contemplated by the FAA.
Since the revised bulletin came out in late March we have been talking with AOPA, the Twin Cessna Owners group, Cirrus Owners, and others including Savvy Engines, Inc. principal Mike Busch, who has provided significant research into the MSB. ABS Senior Technical Advisor Bob Ripley spoke with Continental at Sun n Fun and learned there are only five known camshaft gear failures among tens of thousands of affected engines, and only one of those caused in an inflight engine failure…which resulted in no injuries. Following Bob’s meeting I met with David Oord of AOPA’s Government and Regulatory Affairs staff to review what we and they have learned. We agree it appears there is nothing that would meet FAA's own criteria for an Airworthiness Directive and the FAA has not indicated it is pursuing AD action in response to Continental’s request. We, along with the other groups mentioned above, will be holding a conference call with FAA very soon (as I write this my first day back from Sun n Fun).
If a risk analysis based on real-world failure data shows a significant threat to the safety of flight ABS will be the first to support an Airworthiness Directive addressing this issue. We may join forces with other members to modify the compliance time based on the immediacy of that threat if one is indeed proven. Until a risk is proven, however, the ABS Air Safety Foundation will work with AOPA and other stakeholder organizations to oppose AD action.
Although we are not (yet) facing an AD in the US, many ABS members in other countries are required to observe ALL mandatory service bulletins. We will try to work with Continental to amend this unless/until there is more evidence to support a mandatory inspection, but unfortunately the manufacturer is free to make bulletins Mandatory when it feels they are warranted, and ABS cannot affect regulators outside the U.S. who give MSBs the force ADs have here under the FAA.
For full details read MSB05-8B (below).