COZY: Alum or steel AN fittings in engine bay?
Marc J. Zeitlin
Bill Allen wrote:
Unless you are a far better searcher than I, you will not find such a canonical reference. given the previous discussions we've had on this matter. I've searched AC43.13, the AMT manual, engine manuals and any other official documentation I could find and never found any statement (other than verbal Old Wives Tales) indicating any requirement for steel rather than AL AN/NPT fittings in the engine compartment.
And you won't.
I did and will again say categorically (if for no other reason than to prod other folks who may HAVE such references to post them for the pleasure of proving me wrong) that the aforesaid prescription for steel over AL fittings does not exist.
So you will not find a regulation stating "either AL or steel fittings are acceptable in the engine compartment", because no such regulation either exists or is necessary.
On to logic - since, as Kent Ashton pointed out, Lycoming engines are made out of AL, use AL fittings on their cylinders as they come from the factory, uses AL oil drain return lines (far less robust and at least as prone to vibration failures as AL fittings would be) and these things are single point safety critical failures (see what happens if an oil drain line breaks and falls off your engine), logic dictates that it MUST be acceptable to use AL fittings, and if the top of the cylinder isn't the highest vibration location on a 4-banger, I don't know what is.
Now, there ARE a couple of FAR's that do (or did) address the fire protection issue peripherally, and COULD be interpreted to require steel - these are:
14 CFR Part 33.17(b):
and 14 CFR Part 25.865:
Neither one prescribes a material - they only say that stuff needs to be either fireproof or fire resistant. I will argue that if Lycoming has been making oil return lines for 70 years that meet the requirements of 33.17(b), which are both AL and RUBBER, for Cthulhu's sake, then the AL AN fittings must be at least that capable.
And Part 25 doesn't apply to even small TC'd planes, much less E-AB planes, and really shouldn't be used as an argument for what a small, piston engine plane should need to do.
However, logic rarely convinces bureaucracies and/or folks who've been put in the position of absolute power of anything, so Todd Carrico's recommendation to NICELY ask your inspector, who'd the one making a claim about "requirements" to back up his claim with documentation (of any sort whatsoever) so that you can comply with regulations. You can obviously point out that Lycoming seems to believe that AL fittings are acceptable, since they ship that way from the factory.
If you lose a cylinder (or a prop blade), the engine vibration can only be described as violent. Not sure I would want the minimum material strength possible holding down the job of preventing an accelerant from draining out into my engine.toggle quoted messageShow quoted text
The people who designed the Lycoming are dead now. Its mostly lawyers and 1/2-gineers responsible for the design now, the same people who ate putting shot crankshafts and mags with plastic gears in them in the engines.
Since the invention of the internet its hard to find anything that was written on paper paper in 1960 unless its already on your bookshelf.
Just use the steel and move on.
On Jun 5, 2022, at 01:04, Marc J. Zeitlin <marc.j.zeitlin@...> wrote: