It also makes no sense since so many dual GNS installs were approved under the airframe manufacturer type certificate.
There is nothing special about these. The two GNS boxes may be on separate buses (as they are on the TB series – the avionics bus splits up three ways) but that is a fallacy since there is a single alternator and a single avionics master switch which switches all three avionics bus relays concurrently.
To compound the charade, the above type certificated installation is valid only on airframe serials 2000 and higher (basically year 2000 and later – the GT type) even though the avionics bus wiring has been the same since about 1988.
Some very helpful replies, thank you. JohnR in particular, I appreciate reading “chapter and verse” in your posting above. It seems that what my avionics shop has told me is sadly correct. What a pity!
I wonder what a GNS530w and GTN650 installation would be like. Hmmm. However, I’ll probably just go for the single GNS530w (which is sitting in a box awaiting minor mod approval, to replace my GNS430w) and use that in conjunction with my old King Com2/Nav2 and my yoke mounted Aera 795, which is a great piece of kit.
Thanks again everyone.
Howard
Howard why not dual GTN650s? I had that in the Mirage and it worked well. Or a single 750?
> Howard why not dual GTN650s?
Or one GTN750?
You should be able to pretty much offset the purchase cost of the 750 by selling the 430 and 530. I suspect the work involved would also be cheaper than installing a second GPS.
Why not two 650s? IMHO the 650 is not a great bit of kit – it is touchscreen but another rather tiny screen – just a bit bigger than a GNS430, and anyway I am not sold one bit on the idea of touchscreen for avionics whilst flying…
Why not a GTN750? The cost to install one in my plane would be about £20,000 all in because I’d have change / move other items too. (I have had a detailed quote.) I agree that the 750 would improve situational awareness, but £20k is a lot of money, and it would still be touchscreen (which as I say is absolutely not on my wishlist at all) and the 750 doesn’t show VFR VRPs, which is a pity – if it had then then perhaps that be a good reason to acquire one. Otherwise what does it give me over a 530? A bigger, prettier screen, and that’s about it. (I really don’t need my Nav/com to control my transponder or my radio box). Not worth £20k in my money.
The GNS530w upgrade is relatively cheap. Something like £4,000 all in I think, if I trade in my GNS430w. The 530 has much better situational awareness than the 430 IMO, and that’s really what I’m looking for. I’d rate a GNS530w above a GTN650.
Of course, others will have different opinions. That’s ok.
Howard
Does the GNS530/W show VFR VRPs? I don’t think it does.
You could do what I am doing and wait for the IFD540 to get debugged by a load of Americans 
It is touch screen too but the speed with which its user interface can be driven with the old knobs is impressive. And the touch screen implementation is better / slicker than the GTN750.
The GNS530w does not show VRPs, but it has a much larger and clearer screen than the GNS430w and with an additional display mode showing a compass arc. That’s really what I’m gaining from the upgrade : situational awareness at a glance from a certified box.
I have played with a pre-certification IFD540 a year or so ago at a trade fair. I was not at all impressed, particularly by the screen. I’d need to understand how much better it is than a 530w before thinking about buying one. Right now I’m very happy with my decision, and I agree with you about the American beta testers. Let them play :-)
You could do what I am doing and wait for the IFD540 to get debugged by a load of Americans
The IFD540 is also a touchscreen unit. all functions can be carried out with knobs and buttons as well. It is not certified for EASA. I asked during the IFD540 installers course, when EASA certification was expected, it is not expected anywhere soon although they are working on it.
Howard,
Have a look for excisting approvals for your aircraft. That will give you best value for money now.
Why not a GTN750? The cost to install one in my plane would be about £20,000 all in because I’d have change / move other items too.
I don’t know how many items, this seems quite excessive.
I have in front of me a quote from a UK shop for £14104 plus 20% VAT plus “shipping”, for a GTN750. The unit is £9.9k (which roughly corresponds with the US list price of $14k, no installation so e.g. as sold to Experimental builders) and the installation is the rest. That shop had seen my panel and knew roughly what was involved.
Of course it would be more by the time it is finished because of issues arising, and the aircraft will be grounded while those issues arise so they will have to be paid.
You are right about EASA certification on the IFD540. Could be years, or never.
I have extra cost in installing a GTN750 in my plane- I’d have to change my DME at the same time. At present I have a KNS80 which is very clever but takes up a lot of panel space and will have to be removed if I want to make space to install a GTN750. I’d then have to purchase a separate DME and install it at the same time as the GTN750 install. I’m not going to be doing this unless and until there is a compelling reason to do so. The GTN750 is a pretty box and again I have played with one on a bench at a show. I was tempted but managed to keep my cheque book in my pocket for once, especially after I received the detailed quote!
