2013 Annual Inspection (i)

Yesterday was the first day of N631S's Annual Inspection availability for 2013. My friends at Three Wing Aviation Group will be doing the inspection and associated work package and this year Tony diNuzzo is the IA on the case. I've known and respected Tony for a long time now, and am looking forward to working with him.
Our last flight up from the DC area had been uneventful and I had very few "squawks" to report. The taxi light bulb had burned out a couple of months ago, and the landing light joined it about a month back, so both of those bulbs will require replacement. And the performance of the Shadin Miniflo-L fuel totalizer has been increasingly erratic, so we'll take this opportunity to replace its transducer with a spare that I acquired a year or so ago.

Beyond those tasks, the most notable work-item planned for this year is an inspection of the McCauley constant speed propeller. The prop was overhauled in conjunction with the 2005 Annual Inspection – the first year N631S spent with us – and so it now has about 1,200 hours and eight years SPOH. McCauley holds that the recommended TBO (Time Between Overhauls) is 2,000 hours or seven years, whichever first elapses.

I feel no compulsion to overhaul components at some arbitrarily selected calendar time or time-in-service, as I'm a firm believer in maintenance "on condition". N631S's Continental O-470U engine has a recommended TBO of 2,000 hours or 12 years. The latter mark has long passed and I will cheerfully let the former pass unremarked as well, so long as the engine is talking to me and saying, "I'm fine, boss...let's go fly." And it will do so through spectroscopic analyses of the oil, visual inspections of the filter media and borescope inspections of the cylinders and valves. Ah, but the propeller presents a different problem.

The propeller is a "black box". It doesn't speak to you and there is no way to know that it is sick until something Very Bad happens. Recently, blogger Ron Rapp did a post (which I endorse in its entirety) on Constant Speed Propeller Maintenance, where he describes some of the Very Bad Things that can happen to a sick propeller with terrifying suddenness. I take these things to heart and view propeller maintenance as something you neglect at your mortal peril.

That said, I don't want to "overhaul" the propeller. In the world of aviation, the word "overhaul" has a very specific (and expensive) meaning. It means that you drag out the manufacturer's overhaul manual and do everything that it says to do. But N631S's prop was overhauled back in 2005 and since then has accumulated about 60% of the hours McCauley assigns for TBO. It's just nicely broken in, from the perspective of hours in service, and I'd argue that an overhaul would be premature. My concern is directed more toward the notion that non-metallic parts wear and rubbery things deteriorate more in step with the calendar than with the Hobbs meter. So I've asked Three Wing to take the prop off and send it to New England Propeller (who did the overhaul in '05) with instructions to "IRAN and Reseal". That means, "Inspect and Repair As Needed (to serviceable condition) and renew all fluid seals". Once that is done, I'll happily run the prop for another 1,000 hours before sending it off for "Overhaul".

I stopped at Three Wing this morning and spoke with Tony. He'd done the maintenance run-up and found nothing noteworthy. The cylinder leakdown test had gone satisfactorily. Cylinder #2 was a bit weak at 59 psi (on a day where the minimum acceptable result was 46 psi). Tony will continue and I'll be visiting N631S every day for a while.

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