Failure of 320 Neo to change altitude in autopilot

On the 320 Neo, I select a cruising altitude before takeoff, and after takeoff, engage autopilot. The autopilot handles the navigation (direction) correctly. But the aircraft stays at the altitude that it was at when I engaged the autopilot. And pushing the altitude button either to “engage selected altitude mode” or to “engage managed altitude mode” does nothing. Pushing the vertical speed button also does nothing. The plane stays at the same altitude. Is this a bug or am I doing something wrong? How are you supposed to change altitude while in autopilot?

Ah you’ve discovered the very well documented AP problem that has been covered on here multiple times.


What’s your FMA says? If it says ALT CSTR, that means your aircraft is following the altitude constraints of the next waypoint. You won’t be able to climb even higher until you have passed that waypoint.

My suggestion is, don’t set the cruising altitude from the gate. Set it to the altitude that the ATC clears you during your IFR clearance. Then, once you’re airborne, you change the altitude and press the knob again to engage managed altitude mode.

Thanks. I understand what you want me to try and I will do so. But I don’t know what an “FMA” is, or where to find it. Can you help?

FMA or (Flight Mode Announciations) is the texts that are shown on the top row of your Primary Flight Display (PFD). You can learn more about the topic here.

Primary Flight Display Symbols | Flight Mode Annunciations | Section 8.3.0 (

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