Subtle break in a NAV or GS antenna
These types
are widely used in GA.
They have a habit of developing a break, or a bad connection, at the base where the thread connection is.
You can get the most weird problems with that. In unusual situations e.g. flying the VOR approach detailed here with a subtle equipment defect (see the video here) you could kill yourself. And the accident investigators would absolutely not find out the cause.
The only way to check for this is to get somebody holding the signal emitter (e.g. the IFR4000 test set) to walk around the aircraft, on all bearings, say in 20 degree steps, and plot the signal level at which the "invalid" flag appears. That will detect the fault where one of the two antennae is broken. Obviously, if both work, the polar plot should be symmetrical about the aircraft axis.
Socata use a custom made antenna assembly on the top of the vertical stabiliser whereby two NAV antennae and two GS antennae are fixed in a piece of plastic
These antenna rods
(pic shows the NAV/LOC one) are poorly made. with the stranded wire just bent-up into a hole in a brass block
and after a few years they go open-circuit, largely due to corrosion but also the contact is obviously dodgy.
I reported this to Socata in 2010 but obviously they aren’t too interested. They sell the whole assembly together
for a large amount of money…
The company MAT has been taken over by Amphenol and anyway these are clearly custom (handmade, basically) items.
Has anybody come across anybody else who makes similar rod antennae? The thread on the bottom of the shorter (glideslope) one is M5.
There is a quick fix for a GS antenna which is to use the NAV antennae for the GS as well, and use a CI-507 diplexer (whose insertion loss, at 0.5db, is negligible) to separate out the signal into the two NAV+GS signals. Apparently this is widely done in GA. Obviously the NAV antenna is not quite the right length for the GS (3x difference) but still works very well.
I am getting closer. MAT are long gone (taken over several times) and the antennae are made in the UK
Amphenol Antenna Solutions
Office: +44 1933 408424
Mobile: +44 7718 525604
Fax: +44 1933 408404
I will report when I find something.
Socata sell the whole assembly only and I would be amazed if they have any stock after all this time. But it’s really easy to do the repair. The hardest bit is that the rudder needs to be raised about 20mm to get access.
These antenna rods are more or less guaranteed to fail open-circuit at their base, due to defective workmanship.
I have just been informed by Socata that these are no longer obtainable.
Due to a manufacturing defect (wires loosely pushed into a hole) these rod antennae go bad at the base, after some years.
I am sure there are other sources, non-aviation even, but when I tried to track down the manufacturer (some obscure French outfit whose name was left visible on a sticker) I found they wer etaken over by Amphenol years ago, and nobody at Amphenol (many emails) wants to know. They still make them but only much thicker ones, for cellular etc comms.
These are about 6-7mm diameter at the base, with a very slight taper. The GS ones are about 200mm long and the VOR/LOC ones are about 400mm long (very rough figures).
Peter, Why bother searching out what is likely to be very expencive and/or only avalable in a scrap yard in Catterham ?
I would just seach the web for an american antenna that fits, no one will notice the change and you will be quids in !
I agree (the various avionics shops must be doing some sort of replacement) but find me one that fits 
I did look but didn’t find anything that looked similar. Maybe these things are sold (in aviation) as complete assemblies? That is how Socata sold them.
I have just bought the very last ever set from Socata.
Usualy the VOR antenna is used for both VORLOC & GS via a diplexer, Garmin do this inside the GTN650 and use a splitter if you have two boxes to feed from one antenna.
As Traditional the French use a French solution to the problem and no doubt charge a premium for doing so, fortunatly in the last year or so Robin have got the message about fitting French parts and are starting to use a lot more standard American parts. For some of these they are producing SB’s to allow the parts to be retrofitted.
Certainly one can use a CI-507 (etc) splitter to split out the VOR/LOC and the GS signals, and I reckon there are a number of TB aircraft flying with broken GS antennae and with a splitter quietly fitted…
But that doesn’t solve the problem, and actually the longer antennae are more likely to break anyway.
Update: I bought the last one of these in 2014. No more Socata availability after that.
The picture shows a broken VOR antenna from a TB20.
Has anybody got any suggestions for a repair to the broken fibreglass rod (with a wire running through it).
Or a means of constructing new rods, maybe in stainless steel.
This part is no longer available from the manufacturer.
