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That old story...the resistive fuel sender units on my plane are now old and broken....

My 26 year old TB20 now has completely useless fuel level information being fed to the left hand tank fuel gauge: When the tank is full to the brim the gauge shows three quarters full, and when the tank is half full the gauge shows intermittently a third full and dangerously near-empty. (I do have an accurate EDM700 fuel computer but that doesn’t help me if I have a fuel leak and doesn’t tell me the fuel left in each tank.) I have read that there are two resistive sender units in each tank and these are averaged for the gauge, so I’m guessing that at least one sender unit in the left tank is completely dead or nearly dead.

Whilst such an issue may not be such a problem in a plane with dipable tanks, in the TB series planes the tanks are not at all dipable and when less than 100 litres remains in each tank the remaining fuel is completely out of sight…be there 95 litres left or 5 litres…so the gauges are of some import.

Does anyone here have experience of sorting these problems out successfully on a TB series plane? (..and by the way, after about s/n 1,500, Socata changed to capacitive sender units which are entirely different to the resistive sender unit on the earlier planes like mine)

All help appreciated.


Flying a TB20 out of EGTR
Elstree (EGTR), United Kingdom

I don’t believe Socata designed their own resistive fuel senders but used Renault or other car manufacturers components. For instance the original Bulldogs’ senders were from London taxis and Robin used Renault 16TS parts. The trick is to find out which manufacturer and how the float arm is shaped to suit the TB20 tanks. Some senders can be ‘repaired’ by bending the wiper arm to make better contact with resistive element but that depends on their particular construction.

EGHI, United Kingdom

This is always a problem, locating Renault Socata parts. The car parts business is not set up to locate stuff by the P/N stamped on the item. It is set up to identify stuff by the vehicle it was used on, its year or chassis #. For example I found it totally impossible to buy a Valeo 24V starter relay (spent months on it, contacting motor parts dealers and the completely useless and arrogant Valeo itself).

The fuel sender may be a Valeo part, too.

I would try to get hold of one of these, doesn’t matter if it is broken, and take it (or a pic) to a car parts dealer. But then you have the same issue as I had above.

However a lot of Socata parts are fabricated by some small outfit in the middle of rural France… like these. And others are made by variously obscure homebuilt parts makers, certified by Socata – example

The other approach is to repair it. There should be just a potentiometer in there, which is ten quid at most and that would be a really high quality one. But you need to extract it from the fuel tank, breaking the seal. So you will also need to get a new seal, o-ring, or whatever, but the Socata seals are not usually hugely overpriced. But if you involve a maintenance company they will prob99 not touch a repaired unit without paperwork, so this approach would be done off the books. But they won’t touch a car part either, without an EASA-1 form.

However even buying Socata parts by IPC P/N is hard. Troyes Aviation is totally useless for advice on applicability – they will only order a P/N you give them – and Tarbes is mostly uncommunicative. I am sure they would not do this to TBM owners because most of them have a very good lawyer on a speed dial button on their phone.

Shoreham EGKA, United Kingdom

My experience with fixing resistive fuel level senders is that if they read low and intermittent, cleaning connections and the sender itself will remove extra resistance in the circuit and raise the needle to ‘full’ when the tanks are full. In my case, not on a Socata built plane, the main effort was accessing the senders and wiring connectors. The design on my plane is exactly the same, two senders per wing tank in series.

Peter wrote:

There should be just a potentiometer in there, which is ten quid at most and that would be a really high quality one.


And +1 to go find a second-hand one , repair it then install in place of yours.


Thanks guys…I do find all this a bit depressing. I used to have an old Triumph car and despite its age it was always possible to find new or salvaged parts for it. I guess that was because of the relatively large number built and the consequent remaining demand for parts of course. It’s different with old planes where the initial sales were only a few thousand, and so demand for parts now is not what it is it for those old cars…

I’ll ask my mechanic what he suggests. In the event that he has some good news to report I’ll share it here.


Flying a TB20 out of EGTR
Elstree (EGTR), United Kingdom

There are Socatas being broken up.

One TB10, landed gear up, was broken up (parted out) at Shoreham – I got the last little pile for free.

Google should dig up other ones being parted out. I recall somebody finding some broker selling all kinds of bits.

A year or so ago I found a TB20 being parted out – check your emails.

US Ebay aircraft parts is worth a look; search for Socata. I have just spotted some very interesting bits there, like this and that seller (planepartsinc) might have other stuff.

Shoreham EGKA, United Kingdom

Thanks Peter. That’s helpful.

Flying a TB20 out of EGTR
Elstree (EGTR), United Kingdom
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