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Why do I need a THIRD radio if I want GNS430w + GNS530w (dual GNS certification issue)

I have a TB20 with a GNS430w.
I wanted to upgrade the 430w to a GNS530w which is not a very expensive swap-out / upgrade…and then I thought well, why not keep the GNS430w and simply install a GNS530w as well. (I have room in my panel if I get rid of some “1980s-state-of-the-art” kit :-) )…but EASA say no. I am advised by my avionics shop that because of the risk of common cause failure, if I want my plane to remain airways-compliant, then EASA say I can’t have a GNS430w plus GNS530w setup unless I also add a third non-GNS radio as well, for instance an old King box. This is because EASA are worried about common cause failure of two GNS boxes whilst flying in airways.

Has anyone else heard this nonsense?


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

Has anyone else heard this nonsense?

No. I have flown with quite a few German/EASA registered aircraft with dual GNS installation and no other radio. Some of our IFR trainers even have two identical GNS430s and nothing else.

BTW: At work, we have a small fleet of German registered bizjets (most of which transport category but some part 23) and all of them have sets of two identical radios (Honeyell or Collins) with no third radio of a different model or manufacturer.

Last Edited by what_next at 25 Aug 12:11
EDDS - Stuttgart

Sounds like complete nonsense. Most aircraft leave the factory with avionics from the same “family”, eg dual Garmins in early Cirrus.

LOAN Wiener Neustadt Ost, Austria

Yes, I know that…Cirrus planes often left the factory with 2 x GNS430s…but they may have had some sort of type approval from the outset now grandfathered in. What I am talking about is approval for a modification. I’m told that 2 x GNS is now refused if one wants airways certification.

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

You say “EASA say”.

Who exactly? The British CAA? Your Avionic shop?

There are many airplanes which operate like that and if that is not acceptable, it would mean grounding a good share of the IFR fleet? Almost all the Cirrus planes used to have dual 430 boxes out of the factory, I’ve seen countless Mooneys and Cessnas equipped like that too.

There must be a limit to the random decisions some folks think they are entitled to?

I also understand you can install these things in two ways: Coupled or uncoupled. If they are coupled, there is a certain risk of one influencing the other in case of a failure, if not, they loose a lot of practical value (as no flight plan transfer e.t.c. is possible) but then I’d like to know the reason why any EASA bureaucrat can refuse them in an IFR installation. Possible there is even a way to “uncouple” them as an emergency solution?

I am really interested to know where this is coming from as I am contemplatinng the same thing (dual 430’s to fulfil the 2018 8.33 requirement.)

Last Edited by Mooney_Driver at 25 Aug 12:17
LSZH, Switzerland

I would check with a different avionics shop. Even EASA can’t be that stupid.

EGTK Oxford

I’m told that it works like this : The avionics shop applies to EASA for a modification to be approved. EASA then delegate the matter to a national authority anywhere in Europe -for instance to Austro Control for a G-Reg plane. I’m also told that the shop I use applied for the same mod as I am considering and Austro Control refused it for a PA34, on the grounds cited. Apparently the CAA when contacted, agreed that the ruling was correct.

I know this sounds like complete nonsense. That’s why I have posted on here. I’m looking for a pointer to someone who is connected with such legalities, and not other fliers, who like me, will also think “This can’t possibly be right!”

Help please.


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

Especially the part about Austro Control and a G-reg sounds like nonsense

It is correct however, that EASA have additional requirements for dual GNS setups with cross fill.

EASA considers dual GNS as a major mod. A major mod (STC) can not be done by most avionics shops. A excisting STC or minor mod would have to be used, a new minor mod will always gets rejected unfortunately.

Be sure to also have the aircraft parts catalog (including options) to be checked. It might be approved in the design as an option as well. In that case it should be in the manufactures documentation.

Last Edited by Jesse at 25 Aug 12:58


I had the same problem when I wanted to install a second GNS430W and replace an old KNS80 in my Aztec. It is a major mod under EASA. However, you can put in a GTN650 under a minor mod – at least that is what I was told by the CAA.

EGBW, United Kingdom
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