FYI Garmin GFC 500 - Control Wheel Steering

[Neal]

I have a Garmin G3X experimental with a GFC 500 and roll/pitch servos in my Carbon Cub FX-3. I have the GMC 305 control head but that part is moot.

Did you know...pressing and holding the AP "disconnect" button will actually engage your autopilot? It's called control wheel steering (CWS) and is an option of the CWS config. I learned about this some time ago from a discussion with @craig.roser and it's come up again with another FX-3 owner that had what he thought was an uncommanded autopilot activation. What was happening though was an instructor in the backseat using the button on the rear stick which he thought was push to talk yet CubCrafters by default, on around 2021 and newer use this button as an AP disconnect. But keep in mind this button doubles as a CWS control as well. It may be smarter for the button on the rear stick to be a push to talk and put AP disconnect in the left wing root where push to talk is now. You can option it this way if you ask, no one told me, but I personally think this should be the default config.

Anyways, in helping this new FX-3 owner that this situation happened to I had also been talking to @craig.roser on this feature as he was setting up a new to him RV-14 to use this feature. It's an interesting read in both the G3X pilot's guide and also the installation manual if you search for "control wheel steering." There are other modes I need to explore and learn as well with the FD button but if you're not familiar with CWS and what it's for I suggest reading up on it. From what I understand, take for example you're in ALT and HDG mode and you want to take over control and change heading for example or put it into a 5 degree dive, I believe you can press and hold the AP button and then make your changes as AP will release and then when you release the button it will resume in that attitude. Again, I still need to try this out as I really haven't used it other than verifying what Craig told me long ago that press and hold the AP disconnect will engage your AP. When I flew yesterday I noticed the label at the top of the button and it does show AP/CWS interestingly.

If you're concerned about a back seater engaging AP if they are working radios you can always just turn off the servos (AP) toggle switch above the G3X for fellow cub owners.

So an FYI for some learning an interesting features on the Garmin GFC 500 autopilot system.

Here is a picture from the G3X Configuration side in the Autopilot settings area.

 

[Cactus Charlie]

I learned about this feature when flying the CubCrafters demo FX-3 from the front seat. I called (intended to call) Yakima tower with a position report and landing request and the aircraft rolled right. I asked Brad if he was on the controls then found AP had engaged because I had pressed AP/CWS instead of PTT button.

When I had my own FX-3 I found CWS to be useful for air to ground photography. I'd slow, open the window, roll into a turn to keep the ground subject in view, then engage CWS. The AP then continues to maintain the pitch and roll attitude that I had established leaving me with two hands free for the DSLR.

My FX-3 does not have the rear stick button and I did not know it was an option until long after delivery.

 

[midlifeflyer]

The AP disconnect button tied to CWS and switching the AP on sounds like a major (and potentially disastrous) installation error. I’m pretty sure that would not happen in a certified aircraft installation.

 

[Cactus Charlie]

It is not an installation error. It was a Garmin design choice.

Enabling CWS engagement with a long press of AP disconnect is a configuration option. Don't like it then don't enable it.

I don't like this feature being called CWS because it does not work anything like CWS on a 14 CFR part 25 aircraft.

 

[midlifeflyer]

It is not an installation error. It was a Garmin design choice.

Enabling CWS engagement with a long press of AP disconnect is a configuration option. Don't like it then don't enable it.

I don't like this feature being called CWS because it does not work anything like CWS on a 14 CFR part 25 aircraft.

I agree about calling unintentional engagement of an autopilot by a passenger "CWS." I think you already explained why it's potentially dangerous.

I have flow several certified aircraft with GFC500 installations and have never seen it. Nor as far as I can tell, is engaging the AP by using the DISC/TRIM switch mentioned in the GFC500 Part 23 AFMS, Pilot Guide, Installation Manual, or Maintenance Manual. Perhaps you can show it to me in one of the Part 23 installation manuals?

Edit: Yes, I see the option in the G3X installation manual.

The DISC/TRIM button in all the Part 23 installations I have seen do one of two things and neither are "engage".

 

[Cactus Charlie]

There are numerous references to CWS in the GFC 600 pilot guide - https://static.garmin.com/pumac/190-01488-00_h.pdf.

There are multiple references to CWS in this GFC 600 AFM supplement for the 208B - https://static.garmin.com/pumac/190-02011-07_01.pdf

There are no references to CWS in this GFC 500 airplane specific AFM supplement - https://static.garmin.com/pumac/190-02291-07_01.pdf

I found no generic GFC 500 pilot guide. That functionality seem to be documented in the AFCS section of other pilot guides e.g. G5 and G3X Touch.

I have not attempted to search any part 23 installation manuals but every type certificated aircraft will likely have only the Garmin autopilot features that were specifically included in that STC.

Based on that very limited research I would assume that CWS is not available for GFC 500 STC installations but is available for GFC 600 STC installations.

The experimental installation is not a GFC 500. If it has a system name it is GFC 500X. The GMC 305 and GMC 307 commonly used in experimental installations cannot, the the best of my knowledge, be used in STC installations on type certificated airplanes as they do not include the required redundant AHRS.