Okay folks. To be clear, there are rules in this game and you must follow them. You must "read and accept" the rules at airline creation page so you cannot miss them.
Since intentional hogging of slots is becoming the trend, I have and will, take necessary actions to make sure everyone understands that rules must be respected. I've today closed an airline from this game world that had only 2 planes (1 ops, 1 order) but yet had some 40-45 routes planned with slots reserved to them (of these routes only 4-5 were actually scheduled for the two planes). In this case it is completely clear that the airline only tried to precreate all his necessary routes for fleet yet-to-be-ordered even so that there wouldn't be any problems with slots later on. But this is clearly forbidden in the rules.
Please note that while the rules manual page lists some examples and penalties it is still up to admin to decide the final penalty. In this case the airline was closed (only 2 planes, not a major loss for him) and he can restart with a new airline (without any additional game credits cost of course).
Be also aware that I will implement a tool for admin page to directly view the slot usage of each airline, to show their slot reservations vs. number of active routes vs. number of aircraft etc. But you can still report any probable violations as usual in private to me.
The basic rule would be that once you have the plane available for pre-scheduling (-21 days) you can plan the routes and slots (not exact 21 days, but about a max. month before the plane arrives can be still considered to be done in good faith).
End of note. Have a nice weekend...