Plane doesn't hold altitude in AUTO - Cannot change desired airspeed

Hi everybody,

I have a question regarding arduplane altitude and airspeed control. In my setting, from time to time it happens that when doing mission in AUTO the plane doesn’t hold altitude instantly after switching to AUTO mode. It does hold the Airspeed and is descending slowly.
From the curosities what I have seen is mainly that the airspeed_error is in such cases equal to the airspeed itself and the altitude error works correctly. I have checked doing that with TRIM_ARSPD_CM parameter only as well as DO_CHANGE_SPEED waypoint. There’s also the thing that the Change Speed button in MP doesn’t work and the NumericUpDown that’s besides always shows the value of 100. The curious thing is that I always mess with the same stuff - uploading waypoints with DO_CHANGE_SPEED or without it and sometimes it works well.
Am I missing something here ? I can upload logs from flights as well as settings.

Is ARSPD_USE = 1 ?

That will determine if it’s using TRIM_THR or TRIM_ARSPD_CM

Yes, ARSPD_USE is 1. The curious thing is basically that it keeps the airspeed quite well while basically descending. At first I thought that may be an issue with altitude however as I looked into altitude and airspeed errors (the latter being exactly the airspeed - and the green bar on airspeed scale being shown at 0) I started digging into how to really set the desired airspeed.

I’ve uploaded here the log from actual flight. Takeoff is at 61%, switch to FBWA at 68% and switch to AUTO at 75.8%. It’s visible how the altitude error is increasing while airspeed error is kept the same at -airspeed. The throttle output is all the time 0% while in AUTO mode.

We really need to see the DF (DataFlash) log from the ardupilot itself. That will tell us some very important information at a much higher frequency.

Hi Nathan, I’ve uploaded the log here: https://drive.google.com/file/d/1ulRsFa9WnakvL3MECSWDD_r77iyes6V7/view