AD Requested To Require Camshaft Gear Replacement

Continental Motors’ recently issued Mandatory Service Bulletin MSB05-8B calling for preemptive replacement of cam gears in Continental 520- and 550-series engines (plus a few IO-470s). The MSB calls for tearing down engines with older-style camshaft gears within the next 100 hours in service, or within 12 years of when the engine was built, rebuilt or overhauled (whichever comes first), and replacing the older-style camshaft gear with a new thicker gear (part number 656818).

Continental asked the FAA to issue an AD mandating compliance with MSB05-8B, something that could be extremely costly and disruptive for owners of these engines.

Savvy Aviation of Las Vegas sent an email blast to their mailing list saying that the mandated camshaft gear replacement could affect many more engines than initially thought. According to the company, Continental introduced their “improved” 656818 camshaft gear in August 2005, and started incorporating it into their factory new and rebuilt engines about that time. Continental revised its service bulletin SB97-6B in November 2009 to require that the new-style camshaft gear be installed when the engine is overhauled in the field. So "we initially assumed that any engine overhauled after November 2009 would already have the new-style gear. But that turns out not to be so," wrote Savvy Aviation CEO Michael Busch. "We learned that many overhaul shops (including some of the largest ones like RAM Aircraft and Western Skyways) were continuing to reuse the older-style camshaft gears right up until last month. In fact, RAM Aircraft has an FAA-approved deviation in its Repair Station Manual authorizing them to reuse the gears (if they pass visual and magnetic particle inspection).

"We also found out that the new-style camshaft gears are in very short supply. A check with three major parts distributors (Aviall, Omaha, and A.E.R.O.) revealed that the 656818 gears were backordered for two months, and the expectation was that this situation would deteriorate rapidly as word of the MSB and the possibility of an AD got out to aircraft owners and mechanics.

Although Continental’s MSB05-8B calls for disassembly of the engine, Busch says it is actually not necessary to split the case in order to replace the camshaft gear. It is necessary to pull the engine from the aircraft, mount it on a stand, and remove the oil sump, starter adapter and fuel pump. But the gear replacement can be accomplished without disassembling the engine further. In the case of Permold-style engines, some minor machining of the crankcase is required to accommodate the new-style thicker gear, but that can also be accomplished without major engine disassembly.

"On Friday, April 14, I participated in an hourlong conference call between representatives of affected aircraft owners and key FAA personnel," Busch said. "We requested this conference call in order to gain more insight into the FAA’s intentions with respect to possibly mandating the provisions of MSB05-8B. Participants on the call were:

• Christopher Richards, FAA Engine & Propeller Directorate’s piston engine specialist
• Darby Mirocha, FAA Atlanta Aircraft Certification Office program manager
• David Oord, AOPA Government & Technical Affairs
• Tom Turner, American Bonanza Society
• Roger Whittier, Cirrus Owners & Pilots Association
• Tony Saxton, Twin Cessna Flyer
• Mike Busch, Savvy Aviation

"I found this industry/FAA discussion to be very productive. The FAA participants seemed open and cooperative, and I thought the whole thing had a nicely collaborative feel to it," Busch wrote.

"The FAA participants were not in a position to state what the FAA is going to do about MSB05-8B, as this has not yet been decided. I got the distinct impression that they considered Continental’s MSB was excessive and overreaching. Darby Mirocha stated at one point “We do not intend to mandate the MSB as written.” My sense was that they felt that Continental’s 100-hour compliance time was neither warranted nor feasible, and that the 12-years-since-overhaul provision made no engineering sense (since this is a fatigue issue, and fatigue does not run with calendar time).

"We made it clear to the FAA folks that industry was willing to support an AD that mandated camshaft gear replacement, but only at the next engine overhaul or when the case is split for some other reason (such as cam replacement or post-prop-strike inspection). Whether the FAA is willing to go along with that is not yet clear. We advised them of the parts availability problem, and they assured us that this would be taken into consideration in any proposed AD.

"As the discussion concluded, the industry participants (AOPA, ABS, COPA, TCF and Savvy) agreed to prepare a joint letter to the FAA communicating our concerns and recommendations, and committed to having that letter in the FAA’s hands by the end of April. The FAA will then convene a “corrective action review board” (CARB) to review all applicable information (including our letter) and decide what corrective action (if any) the FAA should take. If the CARB decides that an AD is warranted, then a notice of proposed rulemaking (NPRM) will be prepared and published, and public comments solicited. My best guess is that if there is an AD, its effective date would be sometime in the Fall of 2017 at the earliest.

"All in all, I felt our conference call with the FAA was constructive and encouraging. The fact that they were willing to have such an open discussion with us on the subject said something positive in itself.

"Over the next two weeks, I will be collaborating with my industry colleagues to draft our letter to the FAA. Expect another e-blast update after that."

(Source: Savvy Aviation CEO Michael Bush email blast. Image from file)

FMI: www.savvyaviation.com