COZY: Alum or steel AN fittings in engine bay?

Todd Carrico

On Sat, Jun 4, 2022 at 9:22 AM Bill Allen <billallensworld@...> wrote:
Hi All,

I'm in the UK doing the Annual Inspection, and here we don't have an experimental category, instead we have to comply with "an known and accepted international design standard"

In practice that means JAR or FAR.

So I'm looking for the canonical reference which states that alum AN fittings cannot be used in the engine bay, as I have "been told" by an inspector that they should all be steel.

I see that FAR23.1191(1) refers to firewall components being able to resist 2,000f but that specifically addresses the firewall, and makes no reference to the myriad components in the engine bay far away from the firewall.

 I also see that AC42.13-1B 7.64(f) makes reference to the use of fiber or nylon self locking nuts  not to be used when temps >250F,  but makes no mention of AN fittings.

So I haven't found anything prescriptive about all the AN fittings in the fuel and oil lines in the engine bay.

I realise that in high vibration locations steel may be a better choice, but in more benign use, alum is both lighter and cheaper and easier to find.

I recall that we had this discussion some while back but can't find the thread - I think Marc Zeitlin had some aposite comments - maybe someone else can turn up a regulation that I can use to take down my inspector with, as changing all those fittings is a lot of time and money - even if I can find them.

Maybe I should just paint all my blue fittings black and say they're steel.....  :^)


Bill Allen

My recollection of Marc's synopsis was "Look at all the other fluid carrying things around the engine.  Are they more or less flame resistant than Aluminum?".  I've been on the telling side of that "all steel" argument, but I can't point to a document to back it up.  I'll bet your inspector can't either.  Maybe you can ask the inspector to show you the docs so that you can fully comply with it.  State that you've searched for such a thing, and be nice about it.  maybe point out all the other things in the engine bay that aren't AL or Steel, and see what he says about that.