Thanks to Fenrir mentioning Artie having bumped/bounced on take off during our session last Thursday, finally found and fixed the rather annoying bug where one would be flying along nicely, and suddenly one's aircraft is being removed from midair ... POOF!
That would always occur three minutes after one had landed. Makes sense, we do not want you to have tea and biscuits in cockpit. The mess! (Yes, that's the proper place to have those, apart from ground crew having to clean your pit). Artie bouncing meant the server probably thought he'd landed at take off.
Somehow I've managed to add a test to the removal script, so it will only happen to AI aircraft... and within one minute now, not after three. Now you may think your a/c will stay on the field for like ever after you've landed, but no, unless you stay in the cockpit, once you press escape, your aircraft will be set to AI status, and then poofed after one minute.
Disclaimer: only limited testing has been done, there's a good chance that during the mission running lots of blue ai aircraft occupy their home bases after having landed ... oh well, will deal with that once that happens...