Integrated Autopilots (Advanced EFIS and G3X)
 

Two quick questions...

1. It looks like the Garmin G3X has Altitude Pre-Select from the docs, but I don't see any info that the Advanced EFIS has it. Not sure how important this really is :), but I had a C-182 a while back and that was a major selling point when I bought the plane. It looks like you can set the vertical speed, etc, but not the final alt.

2. I remember reading somewhere that if you lose the EFIS, the integrated AP from TruTrak can still function as a backup to the EFIS, or as a tie-breaker if you are getting conflicting info from 2 different EFIS's. Is this true that the AP will still function w/o the EFIS?

Thanks! Just trying to get a head start on Oshkosh!

Mark Hanley
Finishing the RV-10

Mark:

I've been flying the G3X/GX Pilot combo for several hours now and can answer your basic questions.

As far as I know, the G3X and AFS/AFS Pilot have similar functions. Both can do altitude preselect and vertical-speed commands to fly until reaching the "bugged" altitudes. I'm not sure if AFS has this feature, but the G3X allows you to set either VS or a pitch altitude to hold until reaching the bugged altitude. This plus basic altitude hold, pitch hold without a bugged altitude, and vertical guidance from outside nav sources. The G3X does not allow you to set a desired airspeed, as the Grand Rapids allows you to do, for example.

I know the G3X only syncs to a WAAS GPS approach or will follow internal VNAV guidance when there isn't an external WAAS receiver (such as the 430W) in the system. (My one gripe is that you can't have the system follow VFR VNAV guidance if there is a 4XX/5XXW in the loop; the system is permanently "tethered" to the external GPS.) So for the G3X, the vertical nav modes are only for GPS LPV or LNAV+V approaches; no vertical commands are provided by an ILS approach.

The GX Pilot will function fine all by itself. It'll climb or descend by commanded VS or hold altitude. It will follow GPS-based track or a simple flight plan through the RS-232 data feed. I don't honestly know if it can still decode the ARINC 429 lateral and vertical steering commands from a source other than the G3X.

I don't think the GX Pilot (or the AFS equivalent) works as a tie breaker. You have to choose which source is right, but I also believe that the AP performs all the basic attitude computations internally, and that the link with the G3X is only to receive steering commands. Now, if the G3X goes crazy and sends crazy steering commands, the GX Pilot will follow them, but you can easily revert to totally internal (to the autopilot) modes.

Does that help?

Question for you Marc, based on your last paragraph - can you engage the GX Pilot in Heading/Alt Hold mode without going in to GPSS/GPSV, like you can with a straight VSGV and the GRT? That allows the Autopilot to be a good standalone "backup" to the G3X suite.

Paul

I'm not Marc but I have flown with the G3X and GX Pilot a bit. :) Yes, the GX Pilot can still be operated using its own built-in altitude hold, vertical speed, and track-hold or wing-leveler modes. I'm a big fan of this kind of dissimilar redundancy, as I know you are!

cheers,
mcb

Thanks Matt - yup, that's just the way I like it! There are lots of time I just want the A/P to hold on to the airplane for a second while I do something else, and I don't have to go through setting up the EFIS to do that. Nice.

So it will not follow a guide slope on an SL 30 or a 430 when flying an ILS?

The G3X autopilot interface does not currently support VOR, LOC, or ILS modes.

mcb

Hmmm. I wonder what the next beta package will include, eh? <grin>

I have to say this is the one feature offered by the GRT (and the AFS) that I do miss in the G3X, though living in California it's more that I fly the ILS for convenience and practice than pure necessity. And given that it's for practice, I really should be hand flying, eh?

Actually, the G3X/GX Pilot does this very nicely now. Let's assume you have the AP head powered and ready to go, but you're hand flying. Press and hold the CWS switch, then release. The G3X/GX comes up in roll and pitch hold, so the airplane will continue to do what it was doing when you brought the AP on line. You can then select HDG or GPS NAV for lateral, and decide what you want it to do vertically. But it's just as happy to hold wings level and whatever pitch attitude you gave it.

Hi Mark

The AFS system has altitude preselect, as well as vertical speed setpoint. The system will fly a coupled ILS and GPS LNAV/VNAV approach extremely well. It flies the ILS (and GPS) like it's on rails, MUCH better than the Bonanza A36 with King AP that I used to own. With the Bonanza, close in on an ILS the system would cause the airplane to hunt badly, so bad that you needed to be uncoupled below 500' agl.

If the AFS EFIS goes TU, the AP will keep the wings level while holding altitude and heading. It is a great system. I have not flown behind the Garmin system to be able to compare, but I suspect once the Garmin product matures both systems will be similar in performance.