I am now spending times on Simutrans-experimental. Today I downloaded the recent complied devel-new version (170215_78519e1) and I have found that my airplanes refuse to enter a depot. They just come and go to the front of the nearest depot and the nearest apron.
Even more, they flies along their own route, not to enter a depot, though I have ordered them to enter. As far as I know airplanes enter a depot with no problem in previous version (161223_2d60c8f) if I commend them.
My map is so large (as before; in fact it is the same one) so I uploaded it on the Google drive. Here is the download link. (https://drive.google.com/open?id=0B9oADnQa57kodmx5Wk82WXdaRm8)
I get this happening with trains as well, where clicking "go to depot" will sometimes just make it go to a depot and then turn back without actually entering it, and it will continue on it's schedule, still with 'no load' and then going around indefinitely until clicking go to depot a few more times.
It looks lile you are using my devel-new build, and those are now outdated since James have made proper nightly builds which compiles every day (I manually did it before).
Go check it out, there is a link in the "how to get simutrans extended" thread, the bug might have been fixed :)
Thank you for your notice that there is new version. However, same problem also happens in the new version.
I think that I have fixed this now; I should be grateful if you could re-test with the next nightly build.