The FAA will accept comments until May 22 on a proposed airworthiness directive (AD) requiring potentially costly part replacement prompted by the failure of certain McCauley propeller governor bearings.
The proposed AD published April 7 cites “reports of an unapproved variant McCauley idler gear bearing, part number (P/N) A-20028, that could be installed in the affected governors. This proposed AD would require replacing the governor with a governor that is eligible for installation. The FAA is proposing this AD to address the unsafe condition on these products.”
According to the notice of proposed rulemaking, “all models of McCauley governors have an idler gear bearing with P/N A-20028 installed; however, the unapproved variant of the bearing can be identified by part marking ‘BA-59.’ The non-conforming idler gear bearing could have also been included in the idler gear assembly (idler gear and bearing), P/N A-20107, or the governor overhaul kit, P/N PL-20233 or PL-20234.”
The FAA received 23 reports of issues involving in-service assemblies failing to maintain RPM, hunting, and surging that may have resulted from installation of the unapproved bearings that did not match the design specification.
The AD would apply to about 2,500 propeller governors, with an estimated cost of $85 to remove the unapproved part and an unknown cost likely to range from $1,000 to $9,000 to install the approved part and return the unit to service. An alternative method of compliance is available. Warranty coverage may apply, though owners should expect some expense nonetheless.
Replacement would be required within 50 hours time-in-service after the effective date of the AD, or within 24 months, whichever comes first.
Details about applicability and warranty eligibility are included in an alert service bulletin issued by McCauley in January.