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G3X Pathways

Ezburton

Well Known Member
Patron
I installed a dual G3X Touch in my plane recently and finally got around to entering a flight plan and letting the autopilot fly the route in Nav & Alt Hold modes. This is the first time I have seen the Pathway boxes appear on the PFD. It was about a 30 kt crosswind at 3500' and I was surprised to see that the Pathway Boxes were significantly skewed to the left side of the display, with the velocity vector going through them and the HSI centered.

I was expecting that I would see the boxes in the center of the display since I was on course albeit with a significant crab angle. If the wind had been higher, I wouldn't have seen the Pathways at all. Seems strange if I were IFR. Is there a setting which changes this or comments about the use of or experience with Pathways?

Thanks,
Don
 
I installed a dual G3X Touch in my plane recently and finally got around to entering a flight plan and letting the autopilot fly the route in Nav & Alt Hold modes. This is the first time I have seen the Pathway boxes appear on the PFD. It was about a 30 kt crosswind at 3500' and I was surprised to see that the Pathway Boxes were significantly skewed to the left side of the display, with the velocity vector going through them and the HSI centered.

I was expecting that I would see the boxes in the center of the display since I was on course albeit with a significant crab angle. If the wind had been higher, I wouldn't have seen the Pathways at all. Seems strange if I were IFR. Is there a setting which changes this or comments about the use of or experience with Pathways?

Thanks,
Don

Hello Don,

Don't forget that synthetic vision is heading based (aligned with the nose of the aircraft) since it is meant to give you the same picture that you see out the front window of the aircraft.

When you are flying with a crosswind, the nose of the aircraft can be significantly misaligned with the flight path marker which is showing you "where the aircraft is going".

Since the track of the aircraft is aligned with the course line, not the nose of the aircraft, you will frequently see the flight path marker and pathway boxes (if you use them) off the center of the display when the CDI is centered.

Let us know if you have additional questions.

Thanks,
Steve
 
Another Question

I see the pathways when I use "direct to" navigation and also during the "approach" but I do not see the pathways while on a leg of a flightplan. Is that right?
 
I have a GTN650 with the flight plan loaded. I also have the AP Panel which I used to set the target altitude. After takeoff when I turned toward the first leg of the flight plan, I noticed the Pathway boxes sitting up at altitude (and when I change target altitude, they immediately move with the changing knob... they don't wait until I command the VS or IAS climb mode).

I connected the AP and it flew right to them (once I put in a VS at which to climb). In the (somewhat acute) corners the boxes disappeared due to the rounding of the corner, then came back into view as the turn completed and the second leg became active.

Thanks G3Xpert.... That's what I understood. The flight director was spot on in front of me as it should have been. I guess I hadn't thought that the Pathways were heading based and not track based. I was wondering if they were slaved to the DG, which I think has two different settings.

Don
 
Remember, the G3X/latest Garmin EFIS info is a ?path? based flight display. The boxes (active route) indicate your path. Where the nose is pointed is indicated by the circle with the bulls eye in it - both laterally and vertically. If you takeoff when there?s a substantial crosswind, the bulls eye (heading) will be straight ahead, but after takeoff when you climb into a crosswind and correct your heading to maintain track, the flight path indicator will slew to the downwind side of your heading whenever you are using an active route. The flight path (boxes) indicate where you are going, not where your nose is pointed. When you don?t have a route programmed, the heading/bulls eye will still show crab angle between heading and track based on GPS track information.
 
So, simply put, flight path (as presented by the G3X) equals ground track? Such that they'll only coincide in a no-wind condition?
 
Correct. Its the desired track.

The green pip is your velocity vector and should be going through the center of the windows. Following the flight director should keep you on the ground track and at the selected altitude.

I need to go out and play with this again.
db
 
For me, I prefer flying with the flight director only, all the other 'toys' are turned off.
 
A 430w drives my G3X Touch. What I observe is that the Garmin autopilot will only settle in with the airplane in the center of the HITS boxes when the ball is centered (coordinated flight), when the navigation was driven by the 430w. This is unrelated to winds aloft. I can choose which side of the boxes by simply holding in a little rudder (it takes a moment for the a/p to settle into an offset). Hold in enough rudder and the boxes will almost disappear off to the side. If the ball is slightly off center, it will move the boxes noticeably. Half ball will put the plane outside the boxes.

However, if the navigation is driven by the G3X, the autopilot will always settle in with the center the plane in the boxes regardless of the lack of coordination.

I corresponded with the Garmin G3X guys about this. The explanation was that the course information from the 430w is more sensitive than the G3X's internal one. I cannot imagine how this would cause the observed behavior. Somehow the G3X's algorithms are coupling the degree of un-coordination into the track information, which makes no sense to me.

I don't fly IFR, so for me it was a curiosity. I don't display the boxes anymore.
 
OK

I kind of do what Walt has said. Every now and then when the weather is good and bumpy, with a strong cross wind, if we are on a cross country I will turn off the AP and only hand fly with the flight director up and running. It will challenge you to be a better pilot trying to stay on track and not get to over worked. I think flying in the green is a good idea, so I don't get too dependent on all the easy automation. We don't have Sim's for our RV's so I have to train as I go kind of thing. 2 pennies worth, Yours, R.E.A. III # 80888
 
Follow up with picture

This is what I was describing in the earlier post:

vBl1ARCccxzgFgtVRtDZQ5dGFPEp0cKtGY7l54ik6mV_62wkWHUk7Zt__7EQMo7HiHVP5exyuHqnrUfVfrKDxLkJHF9joytnXjucye5gFmUIBjUGxkoQqa_GTJDF4cvOejzxHFEwdmQR48YYONXeJVoAEd5TxaCHbJe3BP90fQQMPL5WcfMkgsC3h-jS5MHg6wTgc0C0b4jqTyn0wIKKapRBXhuB8RIYF0_yJsPl7gxaDG8GBI0IWtAtpGQW7qDboOjhPsOlNiF_g9FG-XGQF8uaqv-dtH8jsu9UzABF4ExgsaAHlpF-3sqbmASz95PO--Wlty-nwMc6_SCItJgp_m880o9ZmRT_-MowCUPtDVvb4kz1hsLr_bYT5aPvy0L1wn5aoIkKDpvpKVALI2nzzWO1t8vgDoBheyyMLQrgXzkIHa-DySFMxLnMSDkR4LsgCYfqusUyrv7JbePA55VHdJ7u66nokkJz4dZ6X0hal9mYxygRYLyKma868Rxvl1xQ0-rW8diNVmTBsypgyppvNJbFo9RR5LDm5-EZKWuZ-gLgnJfXQEgyjX4TbE4ksoNIYGXTU7jqPiubpuywyL06E5lI2HIC8Kidr95Uq8NjcnZO7sJRZ-GguKbWLjDFabxeEwQhvjuoRVJp4w84z70aR5FzioU7np1fbKPV-_4xZM4a-II6t8FR7lG6wj7XhlaiZZzDC5iRqyiQRIORYCkZv2KYCMEFd7b__oCxxjk=w650-h557-no


This is after the A/P has stabilized. I understand that the rectangular pathways (HITS) should mimic what one would see out the window if those were really in the sky, but this depiction is not that. Indeed, the nose shows pointing directly at the furthest box, even though there is a little crab going on due to a crosswind component (see little airplane depiction on map). The closest box is probably correct, given that the a/p is not on course.

If I center the ball while keeping everything else the same, I can get the "closest" rectangle to center along with the CDI needle after a few seconds.

Again, this does not happen if the G3X's navigation is on internal. The a/p will keep the cdi centered regardless of ball coordination condition.

I do not understand why the A/P would not keep the needle centered (and hence the "nearest" box) just because the ball is 1/4 offset from center when navigating from an external source (430w).

??
 
This is what I was describing in the earlier post:

vBl1ARCccxzgFgtVRtDZQ5dGFPEp0cKtGY7l54ik6mV_62wkWHUk7Zt__7EQMo7HiHVP5exyuHqnrUfVfrKDxLkJHF9joytnXjucye5gFmUIBjUGxkoQqa_GTJDF4cvOejzxHFEwdmQR48YYONXeJVoAEd5TxaCHbJe3BP90fQQMPL5WcfMkgsC3h-jS5MHg6wTgc0C0b4jqTyn0wIKKapRBXhuB8RIYF0_yJsPl7gxaDG8GBI0IWtAtpGQW7qDboOjhPsOlNiF_g9FG-XGQF8uaqv-dtH8jsu9UzABF4ExgsaAHlpF-3sqbmASz95PO--Wlty-nwMc6_SCItJgp_m880o9ZmRT_-MowCUPtDVvb4kz1hsLr_bYT5aPvy0L1wn5aoIkKDpvpKVALI2nzzWO1t8vgDoBheyyMLQrgXzkIHa-DySFMxLnMSDkR4LsgCYfqusUyrv7JbePA55VHdJ7u66nokkJz4dZ6X0hal9mYxygRYLyKma868Rxvl1xQ0-rW8diNVmTBsypgyppvNJbFo9RR5LDm5-EZKWuZ-gLgnJfXQEgyjX4TbE4ksoNIYGXTU7jqPiubpuywyL06E5lI2HIC8Kidr95Uq8NjcnZO7sJRZ-GguKbWLjDFabxeEwQhvjuoRVJp4w84z70aR5FzioU7np1fbKPV-_4xZM4a-II6t8FR7lG6wj7XhlaiZZzDC5iRqyiQRIORYCkZv2KYCMEFd7b__oCxxjk=w650-h557-no


This is after the A/P has stabilized. I understand that the rectangular pathways (HITS) should mimic what one would see out the window if those were really in the sky, but this depiction is not that. Indeed, the nose shows pointing directly at the furthest box, even though there is a little crab going on due to a crosswind component (see little airplane depiction on map). The closest box is probably correct, given that the a/p is not on course.

If I center the ball while keeping everything else the same, I can get the "closest" rectangle to center along with the CDI needle after a few seconds.

Again, this does not happen if the G3X's navigation is on internal. The a/p will keep the cdi centered regardless of ball coordination condition.

I do not understand why the A/P would not keep the needle centered (and hence the "nearest" box) just because the ball is 1/4 offset from center when navigating from an external source (430w).

??

No expertise to add here, but I find it odd that the VVI is not centered in the path box. I understand that the "view" is heading based, but the VVI is an indication of where you are currently moving towards (i.e. more track based). If you are truly on course / level and the flight boxes represent the course, the VVI should be in the middle of the box, by my logic. I must admit that I don't use flight path boxes, so am somewhat inexperienced, but would like to learn more.

I am guessing that the VVI would be aligned with the final waypoint, if it were visible on the screen. This makes sense. However, I don't see the value of a flightpath marker if the closer boxes can't be used to aim or align yourself on the path.

EDIT: I notice on your HSI, that you are around 1* off course. I suspect that is the reason for offset boxes, as this would make sense. You'll hit your waypoint, but you are not on the programmed course line. Next time hit the Direct button and see what happens.

Larry
 
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I have observed the same thing on the boxes. However, I think the green flight path marker is lined up with the boxes and here?s my reasoning. Only 4 or 5 boxes are drawn - as you pass through one, another is drawn farther out. If the full line of boxes were drawn (to the horizon), they would get smaller and smaller right out to the flight path marker. I believe it is referred to as ?parallax?. If you correct to the center line (as the AP would), this goes away, but if you are on a heading to the waypoint, you would remain off center, gradually moving to the center as you get closer to the waypoint.
 
SNIP

EDIT: I notice on your HSI, that you are around 1* off course. I suspect that is the reason for offset boxes, as this would make sense. You'll hit your waypoint, but you are not on the programmed course line. Next time hit the Direct button and see what happens.

Larry

Larry, the entire point of my post was to note that if the ball isn't centered, the a/p will not track the course line, which means the closer boxes are off center. (How far off-center the far boxes are has mainly to do with crab angles, a separate discussion.) If I center the ball, the a/p will correct the deviation from course after 10 or 20 seconds, and the course deviation will be zero, centering the near box. If I move the ball to the left side with right rudder (doesn't take more than a tiny bit), the a/p will stabilize with a deviation to the right of course. The a/p should track the course without regard to whether the ball is centered or not. These offsets on course tracking are not transient - the a/p will fly offset all day long if the ball isn't centered. This seems like an algorithm problem to me.

If the G3X is on internal gps, this phenomenon does not happen. Therein lies another piece of the mystery...
 
In the photo posted, you are off course. The system is taking you to the next waypoint, but is off to the side because when you started towards that point, you were not on course. Likely taking off or something else put you off the direct point to point course and there is no way around that. Hit the direct button and the course will realign from where you are and the boxes that appear to be stressing you out, will line back up. The boxes are off center because you are not on the path....also indicated by the HSI line not lining up. HSI says you need to move to the right and the boxes say you need to move right...so if you want everything to line up....move to the right or reset the course with direct. From what I?m seeing in the photo the ball has nothing to do with the boxes being off center. You are off course.
 
Larry, the entire point of my post was to note that if the ball isn't centered, the a/p will not track the course line, which means the closer boxes are off center. (How far off-center the far boxes are has mainly to do with crab angles, a separate discussion.) If I center the ball, the a/p will correct the deviation from course after 10 or 20 seconds, and the course deviation will be zero, centering the near box. If I move the ball to the left side with right rudder (doesn't take more than a tiny bit), the a/p will stabilize with a deviation to the right of course. The a/p should track the course without regard to whether the ball is centered or not. These offsets on course tracking are not transient - the a/p will fly offset all day long if the ball isn't centered. This seems like an algorithm problem to me.

If the G3X is on internal gps, this phenomenon does not happen. Therein lies another piece of the mystery...

Sorry, didn't catch the original intent. That is odd behavior and I agree it's an algorithm problem. I can see where the s/w might look at yaw or heading deviation from track to determin intercept aggressiveness, but don't understand why it would never ultimately fly on the actual course, regardless of yaw. My first guess would be they wrote the algorithm for their internal GPS guidance first and the external GPS data is missing something that was accounted for with the internal GPS data.

It is also possible that the s/w accounts for this in order to feed data to it's yaw trim routine. This would create a feedback loop to constantly keep the yaw in trim. However, they may have missed a check to insure that a YD is installed or simply ignored that possibility and didn't write the extra code to behave differently if no YD is installed.

Larry
 
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In the photo posted, you are off course. The system is taking you to the next waypoint, but is off to the side because when you started towards that point, you were not on course. Likely taking off or something else put you off the direct point to point course and there is no way around that. Hit the direct button and the course will realign from where you are and the boxes that appear to be stressing you out, will line back up. The boxes are off center because you are not on the path....also indicated by the HSI line not lining up. HSI says you need to move to the right and the boxes say you need to move right...so if you want everything to line up....move to the right or reset the course with direct. From what I?m seeing in the photo the ball has nothing to do with the boxes being off center. You are off course.

I thought I wrote this clearly, but maybe not. If I hit direct-to, it will of course immediately re-center, but will drift again within 10 or 20 seconds to off-course and stay there until I run out of gas. If the ball is centered, this doesn't happen. I can make it run left or right of course simply by putting the ball slightly off to one side or the other. Or, use the internal nav gps of the G3X, then the ball is not coupled into the course algorithm.
 
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