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How could this item be legitimately repaired? Gull Airborne Fuel Conditioner. (also legal amateur avionics repair)

This is a fuel gauge interface; I presume it is for a capacitive fuel gauge system, driving an analog meter.

With legitimate docs, it has been quoted at GBP 10,000 to 20,000 depending on whether it is exchange or outright.

The manufacturing cost is about 0.5% to 1% of that figure.

This is for a Cessna 3xx twin, whose entire value might not be much more than this!

But that’s not the point.

The point is that many of the bits in it are not obtainable anymore (it was made c. 1981). Well, they exist, 100% legit, on Ebay (which is full of ancient “milspec” components, many of which are really great stuff, like hermetically sealed relays) but you won’t get any traceability docs with those But for some you would have to use a different component.

So AIUI the only way to repair it and issue an EASA-1 or 8130-3 is to be a Part 145 company plus a Part 21 company (or a DER, in the FAA system) because you have to select alternative components and write up some due diligence showing they are equivalent.

Of course a lot of stuff like this will be done off the books (witness the number of one-man radio repair shops working out of wooden huts at airfields, fixing this kind of old junk who cannot generate any paperwork at all) but any legit operator will want the gold plated paperwork for CYA reasons.

I wonder whether this is one reason why AOC ops in old piston twins are all but dead. If you have to pay 20k for this awesomely overpriced piece, even once every few years… ?

Administrator
Shoreham EGKA, United Kingdom

If you have to pay 20K for that, one would switch over to a JPI EDM kind of systems, the 900 series include fuel measurements. Will make much more sense.

The main issue with many manufacturers is that they don’t issue schematics AND test specifications. Without test specifications it would be hard / impossible to issue an EASA Form 1 or 8130-3, because you can not prove it is within specifications.

On old equipment a lot of manuals where available, where now for a lot of items you will find that repair is no longer allowed. That is a real shame and IMHO there should be more pressure on this. I was quoted 5900 USD for a CMOS backup battery the other day, which for this manufacturer was not field replaceable. This kind of prices are totally insane. While many shops would be very capable to do the work for maybe 5% of that fee.

Sometimes I find this quite frustrating, as we also have an SMD line for production, and good equipement to do SMD repair / inspection.

JP-Avionics
EHMZ

Peter wrote:

This is for a Cessna 3xx twin, whose entire value might not be much more than this!

I have a complete 310Q for parts if the owner of that gauge is interested .

FAA A&P/IA
LFPN

Jesse wrote:

If you have to pay 20K for that, one would switch over to a JPI EDM kind of systems, the 900 series include fuel measurements. Will make much more sense.

And THAT is precisely what a lot of Twin Cessna owners do !

FAA A&P/IA
LFPN

However, replacing the whole fuel indicating system was not the Q…

Let’s say you had to repair this. What would be the process?

As an aside, all that was faulty on it was one of the three trimpots, but they are not made anymore and a dimensionally identical pot does not appear to exist (you can see this one was made on the 48th week of 1981)

So an official repair needs to somehow deal with the use of a different component.

Administrator
Shoreham EGKA, United Kingdom

That’s an old Spectrol part I think, we used to use them years ago

Last Edited by Neil at 24 Mar 23:12
Darley Moor, Gamston (UK)

Carbon Composition resistors still have their uses, they have a much better failure mode than film types. We still use a few in controls for gas appliances which are considered safety critical

Darley Moor, Gamston (UK)

That’s an old Spectrol part I think, we used to use them years ago

Yes; but if you can’t get the same diameter, potting it is tricky because the epoxy will run down past it. There is a slightly smaller diameter pot around, but 4-turn. Costs about 5 quid.

One has to do the potting in two steps, in such a situation.

Technically, of course, no problem.

The Q is whether one will really scrap the aircraft over something like this!

What would be the 145 company process for a legit repair?

Administrator
Shoreham EGKA, United Kingdom

The 145 company process would be to send it to the manufacture if they are still around for repair. Or to a company that has component overhaul capability for that part. Replace it with a serviceable part, if you can find one. You might be able to repair it under a mod but you will need the repair and overhaul data. Or it never was “broken” in the first place.

Near Luton

Oh for chrissakes, just solder the thing in already!

Biggin Hill
30 Posts
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