FAR 91.213 requires everything installed to work, with INOP placarding OK only until next required inspection

Speaking of widely disregarded:

When I got the turbine, per 91.213, I found out you have to submit a MEL or MMEL to FAA and get it approved (this was news to me). And get a Letter of Authorization from them which in effect is an STC approving you to operate it. Without that paper and approval, you’re technically not allowed to fly the plane. And just like RVSM approval, it follows the user, not the plane.

When I asked around other owners most of them had never heard of it, and those that had, ignored it (“it’s not enforced”). I bet more than 90% of the part 91 or owner-operated turbines fly around technically unairworthy without this LOA.

What to do if:
You have an annunciatior panel with low fuel warning lights
And
You install a primary STCd EDM900 which provides low fuel warnings on its display but no discrete outputs.

You have to placard the old lights InOp – but they can never be repaired or removed ….

Are those lights part of the MEL (minimum equipment list)?

I just saw an aircraft where a KFC325 gyro system was completely replaced by a G600 via an STC and the switches labeled “gyro” etc. were just removed with a cover. I would assume that you can remove them because the STC applies to your aircraft and the STC removes low fuel warning light functionality and is approved to do so.

I don’t get it.

The requirement is for inoperative items to be “repaired, replaced, removed, or inspected at the next required inspection.”.

So it can be inspected, – “yup, ADF still broken” – and that is it.

And given that after an inspection the aircraft can be signed off as airworthy with discrepancies, what else is there to prohibit this?

What if the MEL requires working low fuel lights?

IMO the answer is the STC. It’s an approved modification and it disables the low fuel warnings lights, therefore they can be removed/covered/etc.

In some cases you cannot have a part of a system marked INOP, where the system itself is required for e.g. Day VFR flight.

I don’t see why that would be surprising. If you can’t meet the minimal regulatory requirement to fly, you’re obviously not airworthy without a special dispensation like a ferry permit or something of that nature. So, an INOP ASI would obviously ground you (not that you would want to fly without one), but I don’t think this really applies to something like day VFR with an INOP ADF.