The GNC255 gives you a navcom source for the HSI on the G3x. The suite gives you full IFR flying capability in all phases of flight, departure, en route, and approach.
The ‘just’ G3x happens to be the full suite of instruments needed. And if you install two, you get a back-up for each instrument also. Some designs, like the Flight Design have back-up pitot, and of course dual ADHRS.
The G3x is the panel Flight Design is going with for the C4 which will be a Part 23 certified aircraft, and is already okayd by EASA. The G3x touch provides the GPS/WAAS built-in, two if you put in two panels, flight planning, fully coupled when used with Garmin’s autopilot, AOA, displays ADS-B traffic/weather if so equipped, and is the EFB for charts, sectionals, safe-taxi if you want to get rid of your iPad.
Navcom is old tech fast being phased out in the US.. but adding a $3k GNC255 with the G3x gets you there nonetheless.
@ Peter
Not exactly sure Peter, in this case the equipment manufacturer would supply a data sheet showing all specs either meeting or exceeding TSO, this would be found in the user manual as well and could be the argument for the basis of proof that it meets TSO standards. Whether an A&P would buy into the rationale for GA airplanes and sign it off, not sure.
In my case i could install that radio myself as the builder/repairman and sign it off to be IFR legal, but then still no RNAV approaches for me. Legally, you also can’t just enter the approach waypoints manually in lieu of selecting the approach from an onboard database. On the plus side, under FAA regs I also understand that because dead reckoning is still legal practise in IFR, i don’t need to have an IFR certified GPS on board to fly point to point navigation (like on a direct routing from ATC to the next waypoint) during enroute phase of flight, i just have to promise not to look at the VFR GPS in my dead reckoning calculations i suppose
The EAA have it nicely written up here:
It will be similar in Europe, but more difficult perhaps? because rules are different from state to state, but maybe not.
What the EAA say about transponders:
Note that, while it is required that the transponder equipment meet the performance and environmental requirements of the applicable TSO, it is not required that the equipment be manufactured under a TSO authorization. In theory, this means that you could actually build your own transponder, so long as you can document that it meets the requirements of the applicable TSO. However, the easiest way to be assured that your transponder meets the requirements of 91.215(a) is to install one that has been built under a TSO authorization.
A point here is that there is nothing gained in installing non TSO equipment if it is easier (and cheaper) and more practical to install TSO’d equipment.
Gafunflier wrote:
in this case the equipment manufacturer would supply a data sheet showing all specs either meeting or exceeding TSO
What is the point of exceeding the TSO? What does that even mean? Either it has to be designed according to the TSO, and then built under TSO authorization, which mean the equipment is certified – or it can be built according to the TSO and then somehow tested to show it actually fulfill the TSO. If it is not built under TSO authorization, then every single individual produced of that equipment must be tested to show that it meets the TSO. The whole point of TSO authorization is to make it simpler to produce lots of TSO’d equipment. Theoretically I guess it is possible to produce something that meets the TSO (in theory without actually testing it), but how are you going to mass produce such items and still make the whole process of every single individual meeting the TSO and convincing the CAA that they do, without a TSO authorization? This requires that the testing of each individual is much cheaper than obtaining a TSO authorization.
The thing is, EASA does not specify anything for Annex II aircraft (experimental homebuilds included). Regarding equipment, there is nothing preventing a builder to equip the aircraft according to NCO.IDE.A.125 for instance (minimum IFR instruments according to EASA), if that also meets the national requirements (for homebuilds). None of this equipment needs to be certified in an experimental aircraft. Then for IFR, the navigational equipment has to meet the applicable airspace requirement. As I see it, that is where the problem starts regarding non TSO’d equipment, but also regarding installation of the equipment. For instance Basic RNAV (RNAV 5) has performance requirements as:
B-RNAV/RNAV 5 is defined as RNAV
that meets a track keeping accuracy equal to or better than +/-5 nautical mile (NM) for 95
percent of the flight time. This value includes signal source error, airborne receiver error, display
system error, and flight technical error. This navigation performance assumes the necessary
coverage provided by satellite or ground-based NAVAIDs are available for the intended
operation. In accordance with the terminology adopted by ICAO Doc 9613, Part B, Chapter 2,
B-RNAV requirements are termed RNAV 5.
Clearly the performance is defined in terms of the performance of the system as a whole. At some point the performance has to be broken down to the performance specs of each individual component, but that doesn’t mean the performance of one piece is unrelated to the performance of another, nor is it unrelated to the installation or the aircraft itself. This part is up to the local CAA in each country to decide, and some CAAs are more practical than others.
I think the biggest issues we face with GA avionics is not environmental and possibly functional compliance (which is what TSO is mostly about e.g. temperature range) but
Certification is not concerned with any of the above. Well, not practically. The “production QA” is for sure periodically inspected by the FAA so you just take the inspectors for a nice tour of the documentation facilities 
The KFC225 is a good example. It meets every regulation perfectly. But as a product intended to do a job it’s basically crap. It works great when it works. Honeywell have made at least $10M from the sale of replacement servos in the last 10 years, so no wonder they don’t want to fix it. There are fixes but they aren’t legal.
One thing which does surprise me is that the servos are rated down to -55C which is the full milspec figure. That is actually quite demanding to achieve in a documentable manner. It limits you to passive components, some very old chips, some truly ancient processors (if you use a processor), and probably drives the use of the crappy Globe motors.
The KFC225, huh? ;-))
Maybe you’re a little too negative? I understand that you have more insight into the design etc of avionics than I will ever have, but i can say that I almost NEVER had avionics break in 21 years of my own flying …a roll servo was bad once in the Cirrus (which I do not consider “avionics”) … and the Skywatch failed after 9 years, I had to replace the processor. All the rest of the Cirrus avionics works perfectly and all the time.
In the Warrior I have a GNS430 since 2001, never the smallest problem and an S-TEC30+ autopilot since 2007, same. No, actually one of the cables going to the mode switch on the yoke was bad a couple of years ago (destroyed mechanically) … but that’s really it.
LeSving wrote:
If it is not built under TSO authorization, then every single individual produced of that equipment must be tested to show that it meets the TSO.
There are different methods to show compliance. Certain spec points are typically guaranteed to comply by design. Other spec points need to be tested at the end of the factory line. This is irrespective of whether the device was produced under a TSO authorization or not.
LeSving wrote:
This requires that the testing of each individual is much cheaper than obtaining a TSO authorization.
Yes, trivially so, since TSO authorization means some bureaucratic exercises…
Except you are unlikely to be production testing
Of course a TSOd box won’t be tested either but the compliance means it must meet the spec
Peter wrote:
Except you are unlikely to be production testing
Yes, because that’s usually guaranteed by design. Irrespective of whether you operate under TSO approval or not. Just as I worte.
tomjnx wrote:
Yes, trivially so, since TSO authorization means some bureaucratic exercises…
Well, I think the market speak for itself. There are not much to be found of non TSO’d IFR avionics equipment. The only reason I can think of is it is a much better investment for the builder to pay a bit extra for something that is trouble free (bureaucracy vise), than to pay a bit less for something that may or may not be approved. Besides when reaching that point (IFR capable homebuilt) you tend to want the best, not the cheapest.
LeSving wrote:
Well, I think the market speak for itself.
I don’t know the N reg experimental IFR market. But the EASA reg VFR experimentals I’ve seen pretty much all used non-TSO instruments. So yes, the market has spoken. Against TSO.
LeSving wrote:
Besides when reaching that point (IFR capable homebuilt) you tend to want the best
I agree, if I was going to build an IFR capable homebuilt, I’d want the best, not that technically retarded TSO’d stuff. (ok, to be fair, the GTNs and presumably the IFDs are more or less ok…)
