FSX autopilot not holding altitude

[rumlerm_]

Hi, i bought the game here on steam after I lost the cd I originaly bought in a normal store. The autopilot worked completely fine before, it just started doing it now. When I climb to an altitude I put into the autopilot, e.g. 25000 feet, the autopilot holds the altitude for just a few minutes and then startes to constantly climb and descend. It looks like it can´t hold the altitude by it´s own, even though I have even the autothrottle on the autopilot turned on. I tried everything, even someting with the trim, I don´t understand it though so maybe I made some mistake. It really bothers me, plus after some while when the deflection gets too big the ATC starts telling me that I climbed too much and that I have to descend and vice versa. I tried it mainly on the Airbus a321, but also on other planes, such as the in-game Boeing 737, same problem there. Oh and also, it keeps doing this only when I set the speed of the game 8x speed and 16x speed, when I slow down to 4x speed, it mounts the aircraft back to the altitude I put into the autopilot. Thank you for any reply.

[TextRich]

I have heard of different problems all caused by running the sim time to 4.x and above. I wouldn't use the ATC if I want the sim to run that quickly since the ATC is only designed to handle normal sim speeds. You did state the autopilot worked fine once you set the sim to its normal speed.

[rumlerm_]

Originally posted by BF Bullpup:

I have heard of different problems all caused by running the sim time to 4.x and above. I wouldn't use the ATC if I want the sim to run that quickly since the ATC is only designed to handle normal sim speeds. You did state the autopilot worked fine once you set the sim to its normal speed.

The problem is not with the ATC, the problem is with the autopilot at higher speeds of the game. It looks like plane is "jumping".

[Licopolis]

Originally posted by rumlerm_:

The problem is not with the ATC, the problem is with the autopilot at higher speeds of the game. It looks like plane is "jumping".

The problem actually is with the nature itself. Of course at FL250 you're using barometric setting 2992 on altimeter. However pressure varies at all altitudes so autopilot will be trying to compensate. At higher rates these attempts are less stable, cause whatever speed you use the AP response times stays the same, and impact on trajectory becomes greater.
A jetliner passanger could compare their experience after flying and after having a boat trip - a feeling of being rocked stays for some time (truly not a real sensation but rather residential signals in the brain).

[TextRich]

Originally posted by rumlerm_:

The problem is not with the ATC, the problem is with the autopilot at higher speeds of the game. It looks like plane is "jumping".

That was what I meant. Like Licopolis said, everything gets magnified when you run the sim at super fast speed, including rapid altitude changes, barometic changes, and many other things that aren't easy to compensate for at faster speed. So if you don't want the ATC to complain about incorrect altitude and heading, then fly without using it when you turn higher speed on.