EFIS - is bigger better, or more units better?

I am currently agonising over this. The plane is VFR only, but I want it to be capable of flight in IMC for obvious reasons.

So far, I have sitting in a box:

10 inch G3X touch
G5 backup
Engine monitor box
Magnetometer/ahrs etc
Gmc507 and servos

This started as an exercise to fit two G5s but the cost difference to get a G3X was not big in the end. However I then have all my information, navigation, engine info etc on one screen. But to add a second smaller G3X display as a backup/dedicated engine information is perhaps another £3500 and more panel space. Right now I’m just sticking with the one display.

I’ve flown with GI275s a bit and they are really nice, especially the way it all interfaces together with Garmin radios, xpdr, GTN etc… However when the cost difference is small to get a G3X instead of individual GI275 or G5, it’s a no brainer in my opinion. The G3X is really nice to use and IMO will have a better return on investment when you sell versus a GI275 upgrade. People like glass.

Yes people like glass (a bit like you can’t dispose of a used Merc without the climate control option) but then most people don’t fly anywhere; they just spend 5 digits on eye candy… more if it is raining.

There is a very direct relationship between

• enjoyment of going places and meeting people, etc
• having a low-downtime aircraft

and with “glass” you will get more downtime because (obviously) when something packs up, you lose a whole load of functionality, and quite easily end up with an AOG situation.

Look around any fly-in we do and how many are AOG at the last minute. Or sitting in some “multi-month” Annual. Probably 30%. Look around other people you know and how many are “tinkering” instead of flying. Probably a lot more than 30%. That’s the nature of GA… much of the time the plane is buggered and can’t be used. Or can be used for a short flight but you know deep down that if you take it a few hundred miles you are fairly likely to end up stuck there. And this is independent of how much the thing costs; a lot of SR22s rarely venture beyond Radius X from their dealer.

I am repeatedly grateful for having individual boxes…

GI275 bugs etc

That sums it up nicely. Perhaps add inflight redundancy as an additional factor.

I will digress from the norm in saying I like having redundancy in the form of a vacuum system, but that is digressing from the OP.

IN all cases integration is key and a usual insidious failure in many avionics installs: a single glass is usually easier to get the integration right.

Peter wrote:

then most people don’t fly anywhere; they just spend 5 digits on eye candy… more if it is raining.

True. OTOH one does not need any instrument for flying VFR (legalities set aside). Those are just nice to have
I’ve had quite a few failures on my previous steam driven panels, but none since skating on glass. True, the bigger that glass, the more data displayed on it, the more infos will be lost if. Thing is most of that data is superfluous, the more so in VMC conditions.
My first flight, as most of my primary training took part on this aircraft:

I can’t even tell what instruments were on that panel, since the only thing I could ever see were the shoulders, neck and head of the FI seating in the front seat
Soloed after a few hours, but remember only using the altimeter anyway…

Certainly on tailwheel, you don’t look at ASI on take off, and of course you can/should be able to land without an ASI.

I get the argument about having separate devices instead of a PFD, but vacuum systems are a constant source of problems and mine has already failed. I think having a G3X and a G5 is good reudnancy, two sets of AHRS, air data and backup battery on the G5. If the G3X dies in flight, I lose engine instrumentation but I don’t need that to land somewhere or get home. I do plan to keep a backup oil pressure gauge, just in case.

And if you have AP, the G5 will drive it if the G3X fails, or vice versa.

For the dispatch rate argument, I think this has a greater correlation to people who work on their own planes rather than people with glass panels. Those who do their own maintenance will tinker and work on the plane so it’s always ready to go, as opposed to finding a problem then waiting for an engineer to fix it.

In a nutshell: if I don’t have nothing to do with maintenance or cost of avionics then the bigger the better. The presentation of information is better.

For a plane to own I prefer separate devices. Keeps costs down and allows for upgrade paths unavailable with an integrated device.

Regarding redundancy I stay with vacuum.

Dan wrote:

I can’t even tell what instruments were on that panel, since the only thing I could ever see were the shoulders, neck and head of the FI seating in the front seat

In the Cub here at Værnes (which is a much bigger version, it has a 90bhp engine!) we have plenty of instruments: Airspeed, Altitude, compass, ball, RPM, oil pressure and oil temperature, yes all of this, that’s impressive right? Right we also have a radio and a transponder otherwise we would not be able to have it based at ENVA. But on that version the pilot is seating in front, so as as an instructor I only have airspeed (plus whatever I might see depending on the size of the pilot in the front seat). In Biscarrosse I did a flight to re-validate my CRI in the back of their super cub (with 150bhp engine and amphibians floats) with no instruments in the back and an examiner very tall and with very broad shoulders, could not see any instruments. Still managed to do quite a flew water landings and takeoffs, instruments are overrated :-)

Peter wrote:

and with “glass” you will get more downtime because (obviously) when something packs up, you lose a whole load of functionality, and quite easily end up with an AOG situation.

This is why for at least VFR touring, I like the G5 (or even 2 x G5) rather than one huge screen because if one fails you don’t get stranded somewhere because (in the case of 2 G5) you’ve still got the other one plus the old mechanical instruments, and the failed one isn’t horrifically expensive to get repaired. But it also gets rid of the weight of mechanical gyros.

I still want some gyro instruments in a day VFR plane due to the lack of references you often get over the sea if there’s any haze, but those gyro instruments today are nicer and more reliable as electronic ones, but a large EFIS is too many eggs in one basket.

Peter wrote:

There is a very direct relationship between

enjoyment of going places and meeting people, etc
having a low-downtime aircraft

I´ve put my wine and pizza aside and will throw in a quick five cent.
You referred to redundancy as a primary consideration. You´re looking to buy an SEP and non icing certified aircraft. Do you think you´ll actually be flying lots of IMC approaches to minimums (crisp and clear expensive instrumentation “beneficial”) and in low cloud ceilings and low visibility (on an SEP!). If you do want and expect to risk SEP IMC (low level) flying, then ask yourself what is the most important: pretty “crisp” large glass cockpits or multiple instruments (backup!). Any commercial (“higher” standard) operation requires redundancy and certified instrumentation (for good reasons), as opposed to fancy (dare I say useless..) glass cockpit instrumentation without redundancy. If you want to get rid of the vacuum system (which I as such can´t blame you), then you need electronic back up. It´s tempting to look beyond certified aircraft requirements – just don´t neglect to seriously consider what you´re trading off.

If it was me, I would get an IFR approvable airframe (such as the TB10), that you can upgrade later on in life, and go start out and fly it as is when you bought it (provided it has minimum required obviously!) and get a feel for what is actually important to YOU.
When I was looking at getting my first airplane (not long ago!) I was concerned about getting an IFR approvable aircraft. After I got my airplane (6 months ago (2023)), and have done a couple of cross country VFR flights, I realize that I really don´t need IFR as per se – since I would never plan on an actual requirement to perform an SEP IMC approach or fly in actual IMC conditions (unless high level, level changes, high ceilings etc.). I´ve realized that flying VFR with SkyDemon, solid vacuum instrument-T (as backup to VFR) – does the job by far. I think experience level plays a high role in my perception.

Needless to say, if it was me – I´d go for a couple (or 3) of the 275s. You can even get one at a time – if you fancy. Redundancy! Even keep the vacuum until it brakes (which there is no particular reason why it would – with proper preventive maintenance!). Good luck.