Autopilot not following the magenta line on the ND

[grizzly_air]

Flying from Yellowknife to Ottawa Canada I had a heck of a time because the autopilot was not following the magenta line on the ND.  So I would place it in HDG SEL mode and steer it back to the magenta line.  But when I turned LNAV back on, it steers hard to the side of the line again.  If I watch it on Navigraph charts, it is WAY off, but I figure great circle route perhaps that accounts for the difference on Navigraph, but at the very least I would think it should still follow the line on the ND.   Version 1.32 I am using, by the way.  Latest nav data in xplane and the IXEG    Any idea why I am seeing this?   It wants to stay about 20 miles to the north of the line.

 

TIA

Edited July 20, 2020 by grizzly_air
added screenshot

[Litjan]

hi grizzly air,

I have a hard time seeing it on your screenshot, but the mode annunciations on the EADI look correct.

There are three reasons why the LNAV would not follow the magenta.

First maybe you had a gizmo crash before and closed the window to keep on flying (this may mess up all calculations of the aircraft´s code) or

second the waypoint did not sequence properly (i.e. you bypassed a waypoint too far abeam, so the FMS doesn´t consider it as "passed over").

The second problem can usually be fixed by going "direct" to the next desired waypoint again, so in your case click on the top (highlighted) waypoint - this will put it in the scratchpad - then enter it again on top of itself into the first line. This should give you a "dashed white" line emanating from the nose of the triangle-aircraft-position symbol to the desired waypoint. Hit the lit EXECute button and the plane should turn towards the waypoint.

The first problem can only be solved by clicking the "reboot" option - but that will reset your aircraft to the startup situation, so make sure you pick "ready to fly" first and then "save" the flight like I show in my last video...

The third possibility is that you have discoverd a bug...so if you can reproduce this situation somehow please let us know so we can track down why it happened?

Cheers, Jan

 

Edited July 20, 2020 by Litjan

[grizzly_air]

I had just updated Gizmo as the beta was about to expire so that seems possible, BUT I did get it solved using suggestion number one, but I had to do it a few times to get it to register.   So I’d move it up to the top and exec and the line would draw correctly on the ND, but the plane wouldn’t follow it still.  Did it a couple more times and on the third or fourth attempt it accepted it.  I suspect since I was flying from Yellowknife to Ottawa and the distance was almost 1100nm that might have given it fits as well. 

[Litjan]

Hmm - I will try to recreate that problem by setting up your situation, 150NM northwest of YVO then to BEMOG,...

I will let you know if I can reproduce that.

Edit: Tried to set up your flight as close as possible but the LNAV was humming along very well and went after that magenta like the devil after the poor soul... so I am not sure what is interfering on your end.

I doubt that the long range of the flight had anything to do with it. I recently took it from SFO to Honolulu and that went flawlessly... Also variation and latitude is not special for this flight.

Cheers, Jan

Edited July 20, 2020 by Litjan

[Iain]

Having done far too many 2000nm+ flights in this aircraft, I can also say I have never seen a drift of the line in LNAV, so I doubt it's to do with the route length.