This probably happens not only to a321, but I haven’t noticed it yet on other aircraft. When I set the landing speed my airplane just ignores it and continues to slow down.
I also noticed that when I set flaps 3 or 4 the airplane starts to pich it's nose down up to 10 degrees although the altitude is good at the moment and airspeed is about 170 knots.
Hi there！
Maybe you can pull out the speed button which on the autopilot panel then try again.
( I haven't met this kind of problem yet)
By the way, you know that, when you put more flaps out , the plane will get more force to lift the plane up.So the plane itself need to put the nose down to counteract the lift force. In real life , I think 10 degrees is too much. When I take planes, the whole approache is smooth.
(Looking for your reply)
New here,Luciano
Display MoreHi there！
Maybe you can pull out the speed button which on the autopilot panel then try again.
( I haven't met this kind of problem yet)
By the way, you know that, when you put more flaps out , the plane will get more force to lift the plane up.So the plane itself need to put the nose down to counteract the lift force. In real life , I think 10 degrees is too much. When I take planes, the whole approache is smooth.
(Looking for your reply)
New here,Luciano
Hi, Luciano!
I did some test flights and there was no such troubles this time. I'll send screenshots if that happens again.
Last time that happened the airspeed was controlled by autopilot, I pulled the speed button and set 140 knots for landing. (Thrust levers was in the Climb position and this thing was green)
But the airplane continued to slow down to 120 knots so I had to go around.
Hi,Daniel!
Glad to receive your reply!
Well, a simple way to sovle it is to check out the little triangle beside the speed.(In photo.)
By the way , may I know which autopilot you are using? Aerofly copilot or Airbus autopilot?
170 IAS is high speed for flaps 4 when approach, because aircraft do bose down for supporting descent.
Auto trust (on apprach) only works when the SPEED sign on the FMA is on. Please, check FMA and Speed that selected for maintain
Hi,Daniel!
Glad to receive your reply!
Well, a simple way to sovle it is to check out the little triangle beside the speed.(In photo.)
By the way , may I know which autopilot you are using? Aerofly copilot or Airbus autopilot?
Thanks for the possible solution, Luciano! I guess I was focused on other things and forgot about this triangle. I'll be more careful next time.
Thank you for helping me 
I never use Aerofly copilot because I want to do everything myself, so I use Airbus autopilot.
