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G3X Touch / GTN VOR-to-VOR Autopilot Questions

E

Ezburton

Well Known Member
Patron
All,

I've been experimenting with my G3X autopilot the last couple of flights, specifically flying VOR to VOR and culminating in an ILS approach with a procedure turn. Any inputs / suggestions from folks who use VORs and the G3X AP would be appreciated!

I set up the autopilot in heading mode, to intercept VOR#1 on a specific inbound radial using the OBS function. The autopilot flies the heading and intercepts the radial and heads inbound. I have the inbound course set and then toggle off the OBS to allow the remaining flight plan to proceed (unsuspend).

I purposely chose the inbound radial so that the AP would have to make a turn to acquire the outbound radial. Going through the cone of confusion, I switch the course to the outbound radial. The AP tracks that fine.

Once I reach the switch over to VOR#2 point (the course remains the same, I should just go from outbound VOR#1 to inbound VOR#2), I swap the frequencies and I get a tone in the headset. I figured this was just letting me know that I swapped frequencies. Slowly my course drifts off the radial... turns out, the AP disconnected NAV mode and went to ROLL mode. I saw the amber ROLL indication, and it didn't dawn on me that I had dropped out of NAV. Pushing the NAV button, the course never attempted to get back on the set course.

When I got close to the VOR I switched to the outbound radial and the AP tracked that to the IAF. I switched from VOR#2 to the ILS freq but forgot to arm APR mode and blew through the IAF, so I hand flew around the hold and then let the autopilot capture and fly the ILS down.

So here are my questions:

1) Dropping out of NAV when changing VOR freqs. Why does it do this and is the proper response to just reactivate NAV mode?

2) After reselecting NAV mode, it didn't capture the course which was set. Do you have to steer to a heading which crosses the desired radial in order to reintercept it? (because the AP didn't seem to know where to go at this point)

3) At what point should you arm APR mode and select the LOC freq, right before the IAF? Based on switching VOR freq, seems like no matter what you do the AP is going to change AP modes.

4) If you are flying inbound to the procedure turn using the VOR, will the AP fly the hold and what does it use to do that, GPS or some other logic?


Other Observations:

The GTN simulator won't track a heading to and intercept an OBS course. You can set it up but have to fly it manually.

Very little info is available about VOR usage. The Garmin system seems to be really dependent on GPS navigation. The one training example I found was GPS inbound to the ILS, which then flew the hold and captured the ILS... this worked well for me on for this same approach.

In the G3X, I have the PFD on the left of the split screen. The right knob function can be set when you are in full display mode. The left knob is always Heading and Altitude. I have the autopilot control panel and have been training to always use those knobs instead of the knobs on the display. I wanted to set the knob to Course/Baro but when the split is on the right, it has to be the page control. So I'm stuck with two sets of knobs to set heading and altitude (G3X and AP panel) either have to touch the course box to set the course or unsplit the screen to change the course. Why can't we select the left knob functionality in the config menu like we can the right?


Thanks,
 
GTN VOR

Ezburton said:
All,

I've been experimenting with my G3X autopilot the last couple of flights, specifically flying VOR to VOR and culminating in an ILS approach with a procedure turn. Any inputs / suggestions from folks who use VORs and the G3X AP would be appreciated!

I set up the autopilot in heading mode, to intercept VOR#1 on a specific inbound radial using the OBS function. The autopilot flies the heading and intercepts the radial and heads inbound. I have the inbound course set and then toggle off the OBS to allow the remaining flight plan to proceed (unsuspend).

I purposely chose the inbound radial so that the AP would have to make a turn to acquire the outbound radial. Going through the cone of confusion, I switch the course to the outbound radial. The AP tracks that fine.

Once I reach the switch over to VOR#2 point (the course remains the same, I should just go from outbound VOR#1 to inbound VOR#2), I swap the frequencies and I get a tone in the headset. I figured this was just letting me know that I swapped frequencies. Slowly my course drifts off the radial... turns out, the AP disconnected NAV mode and went to ROLL mode. I saw the amber ROLL indication, and it didn't dawn on me that I had dropped out of NAV. Pushing the NAV button, the course never attempted to get back on the set course.

When I got close to the VOR I switched to the outbound radial and the AP tracked that to the IAF. I switched from VOR#2 to the ILS freq but forgot to arm APR mode and blew through the IAF, so I hand flew around the hold and then let the autopilot capture and fly the ILS down.

So here are my questions:

1) Dropping out of NAV when changing VOR freqs. Why does it do this and is the proper response to just reactivate NAV mode?

2) After reselecting NAV mode, it didn't capture the course which was set. Do you have to steer to a heading which crosses the desired radial in order to reintercept it? (because the AP didn't seem to know where to go at this point)

3) At what point should you arm APR mode and select the LOC freq, right before the IAF? Based on switching VOR freq, seems like no matter what you do the AP is going to change AP modes.

4) If you are flying inbound to the procedure turn using the VOR, will the AP fly the hold and what does it use to do that, GPS or some other logic?


Other Observations:

The GTN simulator won't track a heading to and intercept an OBS course. You can set it up but have to fly it manually.

Very little info is available about VOR usage. The Garmin system seems to be really dependent on GPS navigation. The one training example I found was GPS inbound to the ILS, which then flew the hold and captured the ILS... this worked well for me on for this same approach.

In the G3X, I have the PFD on the left of the split screen. The right knob function can be set when you are in full display mode. The left knob is always Heading and Altitude. I have the autopilot control panel and have been training to always use those knobs instead of the knobs on the display. I wanted to set the knob to Course/Baro but when the split is on the right, it has to be the page control. So I'm stuck with two sets of knobs to set heading and altitude (G3X and AP panel) either have to touch the course box to set the course or unsplit the screen to change the course. Why can't we select the left knob functionality in the config menu like we can the right?


Thanks,
Click to expand...


1. Anytime you manually change the CDI source, the autopilot will revert to ROLL mode from NAV.

2. If you are off by more than a ball or so, NAV will be armed rather than active, and you will have to switch back into HDG or TRK to intercept the course. There is no auto-switching between VOR stations. You have to manually set yourself up for that. Centering the HDG bug and briefly activating HDG mode while changing the CDI source to the next NAV frequency may be one way to anticipate the change to the next radial, while remaining coupled to the autopilot.

3. Generally this is done when ATC clears you for the approach. It must be done before the FAF.

4. The autopilot will not fly a hold when following VOR guidance. It will when using GPS. Normally you would be navigating via GPS up until the point that the FAF is the active waypoint in the GTN flight plan. As soon as the FAF becomes active, the GTN will 'Auto-switch' its CDI from GPS to VLOC, you will track the localizer laterally (needles will change color from magenta to green), and the VDI will populate next to the altimeter. This does not disconnect the autopilot, as it is not a manual CDI change, you remain coupled to the autopilot throughout the procedure.

Auto-switching is an important concept for using the GTN 650 to fly procedures of this type, and is covered on page 6-17 of the P revision of the GTN 650 Pilot's Guide.

Please feel free to send any questions to us directly at [email protected].

Thanks,

Justin
 
Justin,

What about his question on knob action... I am getting a G3X installed right now and would love to be able to use other functions on the main knob since the autopilot has dedicated heading/alt knobs...
 
Justin, Thanks for the response.

1) Dropping out of NAV when changing VOR freqs. Why does it do this and is the proper response to just reactivate NAV mode?

1. Anytime you manually change the CDI source, the autopilot will revert to ROLL mode from NAV.

Just to be clear, I never changed the CDI source, it was always in VOR mode for the entire flight (I only have one NAV receiver). All I did was transfer the VOR frequency from standby to active. I didn't think that would constitute a source change. Going into ROLL mode is understandable when going from VOR to GPS source.

2) After reselecting NAV mode, it didn't capture the course which was set. Do you have to steer to a heading which crosses the desired radial in order to reintercept it? (because the AP didn't seem to know where to go at this point)

2. If you are off by more than a ball or so, NAV will be armed rather than active, and you will have to switch back into HDG or TRK to intercept the course. There is no auto-switching between VOR stations. You have to manually set yourself up for that. Centering the HDG bug and briefly activating HDG mode while changing the CDI source to the next NAV frequency may be one way to anticipate the change to the next radial, while remaining coupled to the autopilot.

The slected radial between the VORs is the same (I was on an airway between CSN and LDN setting up for the ILS 32 at KOKV). So are you saying that when I swap NAV frequencies, if I am close enough to the inbound radial, it will recapture if I immediately hit the NAV button again (that I essentially waited too long and drifted too far off the radial)? It made the turn fine because I eventually crossed the next outbound radial and I had rearmed NAV mode.

This is a real surprise… IMO, the autopilot should not do this. This is basic navigation; there is even a VOR change point marked on the IFR chart where you have to switch the VOR. The AP should pause internally for a couple of seconds and then continue totally transparent to the pilot and only drop modes if the VOR isn’t acquired within 2 or 3 seconds. This is my opinion of course… but prior to the flight I searched the G3X & GTN650 manuals and can’t find anything on this AP nuance. Please point it out if I missed it.
I don’t know what TRK mode is, I don’t have a button for this. I will have to search around for it in the manuals.

3) At what point should you arm APR mode and select the LOC freq, right before the IAF? Based on switching VOR freq, seems like no matter what you do the AP is going to change AP modes

3. Generally this is done when ATC clears you for the approach. It must be done before the FAF.

Certainly. So arm APR mode prior to reaching the IAF, but, don’t swap NAV freq from the VOR freq to the localizer until you are close to the IAF, because the AP will go into ROLL mode.


4) If you are flying inbound to the procedure turn using the VOR, will the AP fly the hold and what does it use to do that, GPS or some other logic?

4. The autopilot will not fly a hold when following VOR guidance.

4 Sounds like before you cross the IAF it would be best to change to HDG mode, cross the IAF and dial the heading around the hold based on the GTN’s guidance to “Turn to Hdg XXX in 3,2,1…”.
 
Last edited:
GTN VOR Navigation

If you change the active NAV source that is driving your CDI, the AFCS reverts to Roll Mode. This is covered on page 344 of the G3X Touch Pilot's Guide, Revision M.

In the case of switching from one VOR to another, you are manually changing your Navigation source. Along the same lines, any time you do this, the autopilot will revert to roll mode as soon as the NAV source it is following disappears. As you cross the VOR, you can change to heading mode to hold your current heading, quickly swap frequencies and re-engage NAV mode to track the new VOR.

If you have an older GMC autopilot controller that does not have a TRK button, you will still have this option on the AFCS menu in your G3X display. Touch the autopilot annunciator and you can select TRK mode. This allows you to follow a GPS ground track rather than a specified heading.

If you are flying a procedure turn, engage HDG mode prior to the IAF, to fly the hold as you suggest. During the hold, make your frequency change from the VOR to the localizer. Once inbound, engage APPR mode and you will couple to the localizer, without the autopilot having ever disengaged or reverted to ROL mode.

If you have any further questions, we can put you in touch with one of our Pilot trainers to walk through your specific flight plan with you.

Thanks,

Justin
 
Knob Assignments

MikeAg03 said:
Justin,

What about his question on knob action... I am getting a G3X installed right now and would love to be able to use other functions on the main knob since the autopilot has dedicated heading/alt knobs...
Click to expand...

In split screen mode, the knobs on the PFD side control heading and altitude at all times, so if you do not have a mode controller, you always have control over the heading and altitude setting. With a GMC mode controller in the panel, there are two sets controls for heading and altitude. This has been brought up before, we will take another look at changing this for those that have the mode controller installed with their system.

Thanks,

Justin
 
g3xpert said:
If you change the active NAV source that is driving your CDI, the AFCS reverts to Roll Mode. This is covered on page 344 of the G3X Touch Pilot's Guide, Revision M.

In the case of switching from one VOR to another, you are manually changing your Navigation source. Along the same lines, any time you do this, the autopilot will revert to roll mode as soon as the NAV source it is following disappears. As you cross the VOR, you can change to heading mode to hold your current heading, quickly swap frequencies and re-engage NAV mode to track the new VOR.

If you have an older GMC autopilot controller that does not have a TRK button, you will still have this option on the AFCS menu in your G3X display. Touch the autopilot annunciator and you can select TRK mode. This allows you to follow a GPS ground track rather than a specified heading.

If you are flying a procedure turn, engage HDG mode prior to the IAF, to fly the hold as you suggest. During the hold, make your frequency change from the VOR to the localizer. Once inbound, engage APPR mode and you will couple to the localizer, without the autopilot having ever disengaged or reverted to ROL mode.

If you have any further questions, we can put you in touch with one of our Pilot trainers to walk through your specific flight plan with you.

Thanks,

Justin
Click to expand...

Okay, I guess I missed that bullet on the freq change. There's no harm in pushing the HDG knob while on the radial, and it seems like it may be best practice to do this. TRK mode I never saw because I never use the touch panel to control the autopilot since I have the 307. TRK does use GPS which is what I was trying to avoid in this scenario.

Thanks for clearing all this up for me Justin. Its better to find out these things before you need them to work. If I get it right this weekend, then I can move on to the next lesson. There is soooo many things to learn on this system.

db
 
g3xpert said:
In split screen mode, the knobs on the PFD side control heading and altitude at all times, so if you do not have a mode controller, you always have control over the heading and altitude setting. With a GMC mode controller in the panel, there are two sets controls for heading and altitude. This has been brought up before, we will take another look at changing this for those that have the mode controller installed with their system.

Thanks,

Justin
Click to expand...

I think I found that if you touch the course window on the PFD, it opens the keypad and you can use the right knob to set the VOR radial. I try not to use the touch so much because its really hard to hit in turbulence, even if I rest my hand on the bezel. I'd still prefer to have my choice of what the knob on the PFD side controls.

db
 
g3xpert said:
In split screen mode, the knobs on the PFD side control heading and altitude at all times, so if you do not have a mode controller, you always have control over the heading and altitude setting. With a GMC mode controller in the panel, there are two sets controls for heading and altitude. This has been brought up before, we will take another look at changing this for those that have the mode controller installed with their system.

Thanks,

Justin
Click to expand...

Thanks! Having the ability to change that would be great!
 
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