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LNAV sometimes skip waypoints

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LNAV sometimes skip waypoints

Postby PedramPedram » Sun Mar 11, 2018 8:45 am

Hi, B773 and A32x(IDG) and probably other aircrafts doesn't follow waypoints as they should in LNAV mode.

sometimes they skip waypoints specially when another waypoint is somehow closer.

example:

Image

https://imgur.com/a/5k8Dz


is there anyway to fix this or this is normal?
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Re: LNAV sometimes skip waypoints

Postby legoboyvdlp » Sun Mar 11, 2018 9:01 am

What speed are you flyinit at? If you are flying it at 250 knots, the turning circle will be too large to execute such a tight turn. Also, you do have the latest version of the IDG-A32X, correct?
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Re: LNAV sometimes skip waypoints

Postby it0uchpods » Sun Mar 11, 2018 11:37 am

I'll make a test and check. Thanks for bringing it up.

Kind Regards,
Josh

PS: use OP CLB/DES (pull Altitude knob) instead of V/S unless you need a specific rate. Its more realistic. It will use speed by pitch to get the best climb/descent rate.
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Re: LNAV sometimes skip waypoints

Postby it0uchpods » Sun Mar 11, 2018 12:56 pm

Hey, I figured out what is happening.

This SID has it as a flyover waypoint. What is happening is this:
Image
The autopilot sees how much it needs to turn at (3500) to make it back to DNZ, so it advances the waypoint command. Then, it sees how much it needs to turn to PUSAL from DNZ, and advances again. This can be corrected by having the FMGS set (3500) to a fly-over, something that isn't supported in the A3XX-AUTOFLIGHT yet. I am planning to add this function to the plane very soon.

Right now, you can fly it, by leaving it on heading manually, until (3500), then pushing NAV. Sorry for the inconvenience!

Kind Regards,
Josh
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Re: LNAV sometimes skip waypoints

Postby Wecsje » Sun Mar 11, 2018 1:38 pm

Actually, the (3500) is showing an altitude constraint on the departure, meaning you should keep RW heading till you reach 3500ft, then turn towards DNZ. Easiest way to solve the issue in this case, is just flying RW heading till 3500ft, then turn right to DNZ. Other option is to set 3500 in the thrust red setting in the MCDU.

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Re: LNAV sometimes skip waypoints

Postby PedramPedram » Sun Mar 11, 2018 3:15 pm

Thanks it0uchpods! I'm looking forward to try new update

Another example for such scenario:

To approach UTAA (Ashgabat) from RIKOP you have to descend from FL170(RIKOP) to FL030(GUDRA) in just 23nm which impossible. so you have to circle around GUDRA until you reach 3000'
UTAA Chart page 7


i used navigraph procedures and the actual chart and i came up with something like this:

Image


Image


but unfortunately autopilot skip circling completely and jumps from ASB10 to FF30R


btw. A32X project is awesome . keep it up :D
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Re: LNAV sometimes skip waypoints

Postby it0uchpods » Sun Mar 11, 2018 4:30 pm

Thank you much for the support and your understanding.

Would you kindly fill out a bug report here so I do not forget in my millions? Thanks!
https://github.com/it0uchpods/IDG-A32X/issues/new

Hope you will enjoy flying the Airbus all the time :)

Kind Regards,
Josh
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Re: LNAV sometimes skip waypoints

Postby legoboyvdlp » Sun Mar 11, 2018 10:24 pm

Wecsje wrote in Sun Mar 11, 2018 1:38 pm:Actually, the (3500) is showing an altitude constraint on the departure, meaning you should keep RW heading till you reach 3500ft, then turn towards DNZ. Easiest way to solve the issue in this case, is just flying RW heading till 3500ft, then turn right to DNZ. Other option is to set 3500 in the thrust red setting in the MCDU.

C.


Why would you set 3,500 in the thrust red setting? That is not standard procedure.

However, you are correct: the correct behaviour would be to climb straight ahead to 3,500 then circle back to DNZ.
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Re: LNAV sometimes skip waypoints

Postby it0uchpods » Sun Mar 11, 2018 11:57 pm

Yeah I don't get that either, that makes no sense. NAV engages at 30ft AGL on liftoff if it was armed, so the THR RED has nothing to do with the lateral modes of the Flight Director Autopilot.

It will be fixed soon and handled like the real plane (I hope!!!)

Kind Regards,
Josh
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Re: LNAV sometimes skip waypoints

Postby Wecsje » Mon Mar 12, 2018 2:01 pm

Should have explained more, it can help in this case to remember to fly RW heading until the lvr climb message flickers. However, you wouldn't do this IRL. In this case, the waypoint in the sim would be wrong as well, since it can not calculate exactly when you will be at 3500ft, in this case, as said before, fly runway heading till 3500ft, then turn right to the VOR (and keep the speed down, the departure probably even has some speed restrictions for the turn ie: 185kts).

To add to the specific arrival talked about here, this would probably not be how it is flown IRL with ATC, I assume this is the RIKOP30A arrival we are talking about, and although it indeed says 3000ft holding at GUDRA, this does not mean it is an altitude restriction. Only at or above FL170 at RIKOP is. ATC would then vector you to one of the 30 runways, and make sure you descend to the ILS intercept altitude in time.

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