The background for this question is here.
On all TB aircraft they built with this option, Socata installed the transducer in the wrong place
where it suffers from massive turbulence. It may be because there is a 90 degree bend (at B) immediately after the transducer, or it could be the weirdly bent pipe before it.
One simple manifestation of the problem is that the instrument-indicated fuel flow varies by about 25% (say 2 USG/hr) according to whether the electric fuel pump is on or not. There should be < 0.1USG/hr variation.
Another one, more difficult for an owner to check due to access, is if the K-factor on the instrument has been set to something significantly different to what is marked on the transducer. The 201B transducer is normally 28500 pulses per USG, IIRC.
On N-reg only, one can apply the Shadin STC and relocate the transducer to the right place (see the link for details). I got this done c. 2005.
I wonder whether any G-reg owners have managed to generate the paperwork to implement this mod. I have not come across a single one, even after an enquiry in the Socata owners' group, which could mean various things, including that some people did it off the books, or they simply don't use the system properly.
There were no replies to this very old thread. I wonder if anyone might have any info, today.
Any route under EASA to move Socata TB fuel totaliser transducer using Shadin FAA STC?
See here
This is quite an old issue. Basically, Socata shipped hundreds of TB20/21s with the transducer in the wrong place, generating a ~20% error. They claimed the DGAC forced them to do it. There is a 1981 FAA STC which supports a relocation to the right location. When I went N-reg in 2005, I applied this STC.
I asked loads of EASA-reg owners if they did anything about it and not a single one responded. I guess they either just do short flights (and ignore the fuel totaliser) or they did the change off the books. I honestly can’t guess which but I suspect the former! But when I asked around, that was before Part-ML and there really was no way short of a Major Change.
Has anything changed?
The single airframe route comes to mind but that requires the co-operation of the STC holder which in this case won’t happen because there is exactly zero $$$ in it for them.
Two threads merged, one from 2013 (no response) and one from 2023 (also no response 
).
People who may know are @wigglyamp or @BAC-Digital-Avionics who is the German distributor for JPI who popped up here recently.
Hello Peter,
I have not yet noticed the discrepancy you describe with the MicroflowL that I have installed, but I have not taken any photos in the area of the fuel system since the last revision, so that I cannot currently say for sure how the transducer is attached to me. I will check that and get back to you.
Br,
Chris
dear administrator,
thanks for sending the link.
yes it is the problem w turbulent flow after 90 deg bending and sometimes also the “hard” transducer installation to the fuselage body.
so 2 enemies of good flow:
1. 90 deg bend
2. hard installation causing vibs to transducer
to avoid this try to make the transducer installation in the hose so the xducer is “swinging” not hard…but smooth, this doenst irritate the flow
and the readings.
there is a company in usa called herber aircraft service making as per stc from shadin hoses for transducers. just call in w stc and plane. they
have all material.
if you have a carburator – in jpi-fs-450 and edm you can set the filter 1 – 2 – 3 which represents the sensitivity to carburator open/close frequency
which generates an up and down in flow rate.
if an fbo or several fbos, individual edm-operators are interested, i could come to a designated airfield in UK for a weekend and hold a seminar
about installations of edm900-960-series, transducers – fuel-flow units, operation of edm-900…family – how to set up, installing, fuel-page for primary
first time settings etc.
over the years i found many secrets not in manual but can be wrong during installation and operation, especially in leanfind and engine before
leaning.
just let me know!
thanks
ingo fuhrmeister
BAC-Digital Avionics
The STC and the physical fix (transducer relocation per the Shadin STC) is not the problem – as I posted.
The problem is doing it legally on EASA-reg because only FAA STC(s) exist.
Some people have adjusted it by adjusting the K-factor, but this adjustment is not stable because the error due to turbulence varies with flow rate. One can probably get it good enough for people to not notice, however.
Hi Peter,
I have the same shit. Fluctuates crazy.
Funny that Socata had your plane for, how long?
It should fluctuate a lot when the electric fuel pump comes on.
It will be interesting if anyone here from the “business” offers a solution 
I don’t expect so because making a living is the name of the game and posting details on a forum is not going to make money.
@terbang mentioned the single serial process here. Maybe his contact knows more.
Peter wrote:
It should fluctuate a lot when the electric fuel pump comes on.
I used to happen at my TB20 until the transducer failed completely. After replacing it just stopped and totalizer numbers were absolutely consistent with FOB. It was long time ago and I don’t remember if my mechanic did something with location or bent pipe.
