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User groups respond to camshaft gear concernUser groups respond to camshaft gear concern

AOPA and several stakeholder organizations whose members could be affected by an airworthiness concern sheet that deals with camshaft gear-tooth failures in Continental Motors IO-520/550 and some IO-470 engines have submitted a joint response to the FAA.

Image courtesy of Continental Motors.

The comments detail users’ concerns about the impacts that provisions contained in a March 28 mandatory service bulletin could have, if they were to be incorporated into an AD without modifications.

AOPA reported that the mandatory service bulletin calls for replacing the camshaft gear “on all engines currently configured with camshaft gear P/Ns 631845, 655430, 655516, or 656031 within 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, with camshaft gear P/N 656818.”

Aircraft operators were concerned with the provisions because replacing the camshaft gear could require significant dismantling of affected engines, including some freshly out of overhaul. The issue was first brought to AOPA through an airworthiness concern sheet (ACS) by which the FAA had sought information from users about their experience with the parts in question before the agency took further action in the matter.

After the elevation of the Continental Service Bulletin to mandatory, AOPA coordinated a discussion with the FAA, American Bonanza Society, Cirrus Owners & Pilots Association, Savvy Aviation, and the Twin Cessna Flyer group “to better understand the issue and help quantify the risk the ACS is trying to mitigate,” AOPA said in an April 30 letter presenting the users’ comments to the FAA.

“Key to that understanding is the need to identify the number of failures (numerator) balanced by the hours of operation (denominator)—a value needed for safety risk management,” wrote David Oord, AOPA senior director of regulatory affairs.

In a recent development, Continental Motors announced that it “is working diligently with the FAA to make significant amendments to MSB05-8B” and making sure owners were not burdened “with unnecessary costs.”

Continental Motors proposed changing the mandatory camshaft replacement to a visual inspection; updating the time limits of the mandatory service bulletin; and publishing alternative methods of compliance allowing camshaft gear replacement “without complete engine disassembly.”

Collectively, the groups stand ready to continue the discussions of ways to mitigate the issue. “We appreciate the FAA engaging with the owner community, early in its review of a safety concern, to assess the risk and explore mitigations that assure safety while not being overly burdensome for the effected fleet,” Oord wrote.

Dan Namowitz

Dan Namowitz

Associate Editor Web
Associate Editor Web Dan Namowitz has been writing for AOPA in a variety of capacities since 1991. He has been a flight instructor since 1990 and is 30-year AOPA member.
Topics: Aircraft Regulation, Aircraft Maintenance, Airworthiness Directives

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