Autopilot balancing on A320

Hello everyone,

I’ve notice something that has been happening for about 1 month now. I’m having an issue with the Airbus A320 that I’ve never had before: when autopilot is set to a certain altitude AND speed, the plane starts to balance because the two variables (altitude and speed) keep changing and negatively interacting with each other.
Here are a series of print screens I took yesterday while descending to Amsterdam Schiphol:


On this first picture, I’ve set the autopilot to 11’000 feet and 240 kts. The plane has been descending from 20’000 feet, then when arriving at 11’000 feet, it starts balancing as you will see on the next print screens. On this one, you can see the speed is increasing (1) and the altitude is decreasing (2).

On this picture, about 7 seconds later, you can see the speed is now decreasing (1) and the altitude is increasing (2).

Then the speed increases again (1), and the altitude decreases again (2).

The plane keeps balancing like that and the only way I’ve found to stop this is to deactivate the altitude autopilot and stabilize manually the plane horizontally so the speed stabilizes itself and then I can set the altitude autopilot again.
The problem is that when I set the altitude to 11’000 feet for example and the plane is descending from above, it usually descend to 10’800 feet before “understanding” it’s too low, so the speed autopilot reduces the throttle to 0% (which brings the speed to approximately 235 kts), as the plane climbs the nose to reach 11’000 feet, the speed increases suddenly and goes up to 245 kts and the plane reaches approximately 11’200 feet, and the vicious circle starts here, where the two parameters are negatively affecting each other. I fly the A320 very often and this is new.

More details :

  • The problem occurs at any altitude.
  • Setting the VS to maximum -500 ft/min seems to fix the problem, but when you have ATC asking you to change your altitude, it’s frustrating if you can’t change more than -500 ft/min.
  • A new bug on the A320 I’ve noticed, when you set you flaps to position 1, the nose climbs to +15° and the plane starts to climb up even if you have your autopilot set to a certain altitude below and you VS set negatively (-1’000 ft/min for example).

That’s it, sorry for my English mistakes and I hope I explained it well. If you experience the same troubles or have any explanation thanks for you help.

4 Likes

I had the same problem, but he left. Actually I think you have to go to 240 kts under 10,000 feet first and then 340 kts. When you reach a certain altitude the speed limit will drop. At 33000 feet it will be at max 300 kts. Personally up to 15000 feet I have a vertical ascent of 2500 feet / min and as I go down to 2000 then 1500 then 1000. My cruising speed is 296 kts.
If this keeps up, it means there’s really a bug. 🤔

2 Likes

I agree that there is a bug with Autopilot in general.
I was in the C130 and using autopilot to fly and everytime I turned ap on, the planes starts porpoising very violently till stall. The only way to fix is to disengage ap and fly manual. It’s very frustrating, especially for long flights.

I’ve noticed that with the A320 family, you put the vs down from 0 to -1000 fpm and it will go down to -1500. The whole system needs a finesse really !

This is a known issue, but hard to replicate - for some reason it doesn’t affect everyone - FDS is looking for a fix.

Side note: I also have the same issue. A320, 77W and the Dash-8 all have the same issue for me.

1 Like

Setting trim might help. As for the flaps issue with the A320, the trim will stabilize the 15 degree pitch.

i have same issue and i’ve found out that is related to pitch sensivitiy.Interesting… you can try different sensivities and see if it’s stabilize on what you set.

1 Like

Finally I have this problem but with the A321. I don’t think the other planes have that problem.

I get you here on the 321

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