Aircraft does not follow speed and altitude restrictions properly during approach - Serious VNAV problem

[ekosif]

Hello, 

I will try to explain with help of a few screenshots:

As can be seen from above, there is a altitude restriction at SISPI, which is at or below FL280. But aircraft descend profile is not following it and it starts descend just before the waypoint. In this case, it is not possible to be at/below FL280.

 

Second case during the same approach, again as can be seen, even though I have already passed 11000 feet restriction and also another 11000 feet restriction in front of me, VNAV shows FL142 is on track. Also, during this time, aircraft is not descending and stayed leveled, so it is not overshoot issue.

 

 

Also again during same approach, even though there is a restriction on the next waypoint which is between 5000 and 6000 feet, VNAV is not following it. I switched to OP DES to catch it but it shows I am 4700 feet below at this point according to VNAV. 

 

 

And also here, there is a speed restriction there (not below 210 know, it is at 210 knot) aircraft activates the approach mode and disregard the speed targets.

If you also look at the VSD, it shows I will climb first and then I will descend again.

Edited August 7 by ekosif

[iniSteven]

Hi Ekosif,

I've been working on tracking the VNAV system and documenting its behavior for the dev team. I see you're flying an arrival here, but you could let me know the specifics of which arrival? I will try and fly it myself to see if I can recreate the issues.

Best,

Steven

[ekosif]

2 minutes ago, stagre said:

Hi Ekosif,

I've been working on tracking the VNAV system and documenting its behavior for the dev team. I see you're flying an arrival here, but you could let me know the specifics of which arrival? I will try and fly it myself to see if I can recreate the issues.

Best,

Steven

Hello!

Thanks for your interest.

It was the flight from Antalya(LTAI) to Istanbul (LTFM), SISPI1A arrival, ILS 35R. 

I am also attaching OFP here in case it helps.

Thanks!

LTAILTFM_PDF_1754520514.pdf

[iniSteven]

1 minute ago, ekosif said:

Hello!

Thanks for your interest.

It was the flight from Antalya(LTAI) to Istanbul (LTFM), SISPI1A arrival, ILS 35R. 

I am also attaching OFP here in case it helps.

Thanks!

LTAILTFM_PDF_1754520514.pdf 833.57 kB · 0 downloads

Thanks! I will see if I can recreate.

[dectenor1]

On 8/8/2025 at 12:29 AM, stagre said:

I've been working on tracking the VNAV system and documenting its behavior for the dev team.

I have made various reports on issues relating to VNAV stuff, F-PLN page predictions and how these are displayed, managed speeds, and again how these are displayed, constraint behaviour etc., etc. Please feel free to reach out for any info that may help in this regard. VNAV related things need a LOT of work currently!

Best

[iniSteven]

8 minutes ago, dectenor1 said:

I have made various reports on issues relating to VNAV stuff, F-PLN page predictions and how these are displayed, managed speeds, and again how these are displayed, constraint behaviour etc., etc. Please feel free to reach out for any info that may help in this regard. VNAV related things need a LOT of work currently!

Best

Hi Dectenor, 

Yes, I've seen your thread as well and been going through it. Definitely agree the VNAV needs work and that is something I am working with our RW A350 pilots on helping to improve.

Best,

Steven

[ekosif]

On 8/10/2025 at 12:19 AM, iniSteven said:

Hi Dectenor, 

Yes, I've seen your thread as well and been going through it. Definitely agree the VNAV needs work and that is something I am working with our RW A350 pilots on helping to improve.

Best,

Steven

Hello @iniSteven,

 

Is there any update on this one? I made another flight right now again to Istanbul airport and aircraft made the same behaviour again, it's not following the restrictions during approach.

 

Also, even though it has been reported many times ago, HUD alignment is still not correct. When should we expect any update for it?

And also, Landing checklist is not correct for flap item, it turns to green on flaps 3 even though full flap landing is configured. 

 

Unfortunately, we are not getting any update especially for MSFS 2020 even though some major and critical features are not working correctly.

[DaVsoN]

I also have the same issue on pretty much every approach. The aircraft doesn't want to follow altitude constraints and messes up the whole approach path. When will this be fixed, because me and several other people don't have a working aircraft right now.

[ekosif]

Helloooooooo!!!! @iniSteven @iniBuilds

VNAV is NOT working properly, are you aware of this? 

[Xenon341]

Hello,

VNAV has been updated in 1.1.6, specially the TOD calculation. You should see some enhancement.

From the dev team :

Quote

For context, the specific issues that were fixed were that it was miscalculating TOD, so it would always miss high altitude constraints, and then it was having issues where it would under estimate drag and would oscillate betwene THR IDLE and SPEED modes

Works still continue for other cases like sequencing closely spaced waypoints with restrictions.

[dectenor2]

2 hours ago, Xenon341 said:

From the dev team :

Where was this taken from if you don’t mind me asking?

[Xenon341]

IniBuilds Discord server.

https://discord.com/channels/535246634448191499/1292807978986111046/1424997127007895617

[dectenor2]

1 hour ago, Xenon341 said:

IniBuilds Discord server.

https://discord.com/channels/535246634448191499/1292807978986111046/1424997127007895617

Thanks

Link doesn't work for some reason.

Must be banned despite the countless hours I have spent testing and making detailed reports to try and help the product improve.

Edited Tuesday at 03:13 PM by dectenor2

[ekosif]

On 10/7/2025 at 5:06 PM, dectenor2 said:

Thanks

Link doesn't work for some reason.

Must be banned despite the countless hours I have spent testing and making detailed reports to try and help the product improve.

I don't think they banned you, there must be some other issues

[iniSteven]

Hi all, have you had a chance to try 1.1.6? We've made some changes to the VNAV logic and it *should* be much more accurate during the majority of the descent. We still have a few more fixes coming in an update shortly, including tuned wind correction and some CDA adjustments as it transitions onto approach - but for the majority of cases from TOD down to ~3000agl it should be much more accurate.

Also @dectenor2 we've gone through some discussions with our SMEs regarding the behavior at hard altitude constraints, and from what we can find it is accurate behavior that the aircraft attempts to level off in ALT CST*. So you can rest easy that when the aircraft gets high on path in that situation, you are truly immersed in the real Airbus experience 🙂

[dectenor2]

35 minutes ago, iniSteven said:

Also @dectenor2 we've gone through some discussions with our SMEs regarding the behavior at hard altitude constraints, and from what we can find it is accurate behavior that the aircraft attempts to level off in ALT CST*. So you can rest easy that when the aircraft gets high on path in that situation, you are truly immersed in the real Airbus experience 🙂

Hi, good to hear from you.

I think that what the aircraft ACTUALLY DOES is very good, it’s just a lot of the indications and information provided on various systems pages about what the aircraft is GOING TO DO is incorrect.

For example, I have actually never had a problem with an aircraft meeting altitude constraints or being at the correct speed. It’s just the indications given about these are broken. Things like the ND and level-off arrow indicating you’re not going to make a constraint, but the F-PLN page saying that you are going to make it. You do actually make it, it’s just you can’t actually tell that from the various sources you would use to check if you are going to because they’re broken.

Or on PERF pages, the aircraft does in fact target the correct speed restrictions, but the PERF page gives the completely wrong target speeds.

Or the aircraft actually does target a MACH, but the FMA and FCU are telling you that it’s targeting SPD.

 

Etc., etc., there are many examples of behaviour like this.

 

I hope this makes sense, I think that what the aircraft does is very nice, and has certainly improved with recent updates, it’s just the information provided about it is incorrect.

 

A lot of this stuff I have already documented (dectenor1, I had to make a new account as the forums stopped supporting Facebook login). But more than happy to go over it again. I have a lot of free time at the moment and would be more than happy to go through all of this again, or do it and send it to you directly if that’s more useful.

 

It’s exactly the same situation with the A340 as well, in terms of lots of indications and information displayed being incorrect, but the aircraft itself does a good job.

 

It would be great to really try and get this stuff fixed and I’m sure it could be easily applied across the entire fleet once the logic is correct, which would really enhance all aircraft.

 

Of course, thanks for all the work as always. And please, please, do reach out if you need further information, or I can be of any assistance at all in these matters. Both the A350 and A340 would be a joy to behold for me and many others if these things could get fixed, rather than always having that feeling of looking at something displayed on the F-PLN page for example and knowing that it’s just incorrect.

 

Sorry, long message, but as you can see, I’m passionate about this project and really willing to spend plenty of my own time helping it improve!!

 

Thanks again!

 

Edited 42 minutes ago by dectenor2