It turns out that the GTN750’s AML STC would not be valid for my TB20GT because I have the “wrong” Shadin fuel totaliser.
A post by Garmin on a US site:
I wonder how many people are aware of this.
In Europe, FAA Field Approvals are almost impossible to get done (I have done two, both via helpful people in the USA who presented them to a US FSDO on my behalf) and the same issue applies to an EASA STC.
However I wonder if changing the fuel totaliser is a Major alteration anyway (on an N-reg especially). If you had one type of Shadin installed (forget the GTN for the moment) you could without question pop in another similar unit, as a Minor alteration. That is done all the time in the USA.
It’s not that strange is it? They can’t test any combination, so they list some equipment which they have tested. If it is not in the list, either it should not be connected, or that part should be replaced by something that is supported.
This is a good thing about Aspen, they support a lot of older equipment. Garmin tends to support only more newer equipement, which is fair as well for such high end equipment. It is a bonus that Aspen does.
Any installer will found out before the installation, as they have to fill in a very long checklist, in which installation choices are to be made, and a motivation has to be given including reference that what they want is approved.
So not such a big deal, either choose to not connected it, apply for a change (which will be hard, because how can you prove it works?) or just upgrade the fuel flow. Shadin has a digiflo and miniflo STC for TB-20, so that shouldn’t be a problem either.
You can prove it works by connecting it. That’s all that Garmin would have done.
I am sure many installations ignore this rather technical/legal aspect… especially since you can leave the wires off, with a little connector, and re-make the connection after the installation. That has been widely done e.g. with the Socata TB non-rotating stormscope display (the DGAC banned it from rotating because it might allow the pilot to use the stormscope to avoid thunderstorms!).
The other flowmeters are the wrong size/shape for any factory-hole in a TB20.
I don’t understand why someone wouldn’t just solve it legaly. Send one E-mail to Shadin, ask if they use the same dataprotocol, if so (likely) apply for it.
Just hooking it up saying it works is not “approved data” so will not be acceptable to either FAA or EASA
It’s very hard to get an FAA field approval done in Europe.
But that’s assuming this is a Major mod. I think it may not be.
Is there a list somewhere of what fuel totalisers are approved for the GTN750?
Garmin Doc 190-01007-A3 “GTN 6XX/7XX AML STC Installation Manual”, Section C.3, Table C-3:
Shadin
8800T
9000T 1
9200T 1
F/ADC-200
F/ADC-2000
91204XT(38)D (Miniflo-L)
91053XP (Digiflo-L)
91053XT-D (Digiflo-L)
912802-( ) (Digidata)
1 This source must not be connected to the GTN if the GTN is the pressure altitude source for a Mode S transponder.
OK – I should have known – that PDF is in my 15GB collection 
I don’t think any of these are 2.25" units, and the Digidata has been discontinued anyway.
I would not mind replacing my Shadin with a unit that is a bit more sunlight-readable but there isn’t one I can see.
can’t you use the fuel flow option on the EDM and hook it up that way to the GTN?
Yes I could do that – swap the EDM700 for one with the fuel flow option. My EDM700 is actually the bigger 3.125" version.
But then I get the horrid user interface of the EDM700, which I don’t normally have to mess with, but would have to regularly mess with if I used it for fuel flow which (as well as the redundancy) is why I prefer a separate instrument for fuel flow.
What about one of these bad boys?.
https://www.jpinstruments.com/shop/edm-8301/
This is what i have in the commander hooked to the GTN’s, its a brilliant piece of kit, had to kick out the old Shadin as it spoke with forked tongue!
Not familiar with TB20’s so not sure if you could fit it in?
