Why are the A/P controls not smooth for the narrow-bodied aircraft?

Through past experience of flying the A318, 9, 20 and 21, I found a similar problem with the A/P among all of them. The A/P VS button when adjusted, causes the aircraft to jerk up and down violently even with no wind. I find it hard to keep the aircraft stable when adjusting the VS. I can try flying manual but me hand-flying is equally as unstable as using the A/P VS, please solve this issue thanks.

This issue also occurs on the 787 as well.

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This happens when you are not already stable with the correct altitude for the approach. When applying the APPR, it will try to find the correct altitude. It may do a couple acrobatic jumps and swings

Are you adjusting it with 100ft/min? Don’t slide it so far up/down and it’s usually pretty smooth.


It doesn’t happen all the time. Sometimes when I adjust the VS by + or - 100fpm, it seems ok. But when I increase the VS to 700fpm via 7 100fpms out of these 7 adjustments at least 1 will cause the aircraft to jerk.

I don’t adjust with + or - 200fpm as it will surely cause my aircraft to jerk like crazy.

I would recommend that you try to screen record this. I’ve done this several times and i can’t say I’ve noticed anything like what you’re describing to be honest :)


I knew someone would ask me this, I’d already have screen recorded to make this easier to understand if I had the app and so far the screen recording apps are making my phone and IF lag and hot.

Can someone also input their findings? I also don’t know why this has been moved to General when it’s a bug.

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I forgot to mention that this is about me descending from TOD changing the VS from 1200 to 1000 to 700 so as to slow my descent and not when I’m near the ILS.

And I assume this got ignored, great!

You have to apply the AP smoothly too, it’s a magical thing, but you have to help it a bit

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I’ve seen this too, with a range of aircrafts.
During a descent, changing the vertical speed, causes vertical shaking of the aircraft. Nothing major, but not pretty.


Shame you are having issues, I have a fair amount of experience on those aircraft and have not seen the issues you mentioned.

Suggestion which might help is when programming in your next FL ( from TOD as an example), rather than going down in 1000 or 2000ft steps until you reach your FL straight away, start off in small steps of 100ft until you reach 1000ft below your current FL then use the bigger steps to reach your planes flight level. Then go back and change the VS from -250 up to -2500.

Ie FL is 350, you are at TOD and wish to go to FL120.

First go from 350 down to 340 in 100ft steps, then down in 1000 / 2000 ft to reach FL120 on your AP. VS should still be at -250 ftpm. Now change your VS to -2500 rpm ( or what ever you have planned), this should keep it nice and smooth

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If it’s not pretty I still have to say it. If I keep quiet now they might not know and not include in the update (if there’s one).

I don’t get what you’re saying. You mean to go slow on the VS initially and then increase VS? The issue I’m facing isn’t about going slow or going fast in VS. It’s about how the A/P responds when I change the VS. Even if I go slow initially by descending -100fpm and change from -100fpm to -2500fpm like what you said, the aircraft is still going to jerk unless I do the adjustment very slowly, which means I’ll take probably 1 minute to adjust from -100fpm to -2500fpm. I’m a very sensitive person.

Well not sure what else to suggest, that is the only issue that I am aware of , and by changing first the ALT in small steps and then increasing by larger steps to reach the desired Alt and then do the same on the VS, this controls it.

Changing the ALT in small or large steps still causes my aircraft to jerk, even for the 787!

This is honestly going to be a configuration error of some kind.

Information needed

  • Altitude at start of descent
  • Speed at start of descent
  • A/P engauged (NAV, HDG, SPD, ALT, VS)
  • Triming (Purple line not present prior to changes)
  • Steps to reproduce (First, Second, Third, ect.)

If I’d have to guess without this information I’d say you are either
A Fast or slow on your airspeed
B Trimmed incorrectly
C steps of use are incorrect

If you could provide the steps you took to get the result consistently we can address it.

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Assuming an A321:

Altitude at start of descent: FL 360
Speed at start of descent: M 0.78
A/P engaged: NAV, HDG, SPD, ALT, VS (All)
Trimming: 25%

So to start off my descent, I just adjust ALT from 36000 to 0. It doesn’t matter whether I straightaway reduce by -2000 or -100 from the start it still causes my aircraft to jerk.

Another way I start my descent is to disengage ALT and VS and hand-fly my aircraft to descent at -1200fpm VS. I find this way better than the former.

Next, I’d reduce my VS to -1000fpm as I don’t want to be below FL 300 until 200nm or nearer. Reducing the VS by -100fpm or -200fpm makes no difference unless I adjust slowly. By that I mean it takes 1 min or longer to adjust from -1200fpm to -1000fpm.

No, as the pink bar can be barely seen and I was at M 0.78 at TOD.

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