Even though I'm not part of AC (or any game at the moment), I feel I should say something about slots.
As it is now, it seems like many players think they should be able to grow the entire time the game world is on. And without a major delay in it.
However, like we know, this can't be the case, nor should it be. As in real life, businesses can't grow exponentially. Though for a couple of years Apple has done that with iPhones, but that's about to change, as other companies get into the markets as well.
So my point is, that this game is much more than just growing up your airline. It's of course that at first, but after that, it's keeping your company running, prospecting, and ahead of every other company. That's what the airline statistics are for.
Now, about the slots. I don't know much about how they are given in real world, but as it was pointed out, the airports probably want as many passengers coming to their airport as possible. Thus, after the initial start, as the slots start to come slowly, I think they should be given in an 'auction'.
So, an airport could inform (for exmple in a news item) about upcoming slot auctions. Any airline could then participate by making an offer on how they will use the slot. There could be a form for this that has some required fields like plane to be used on that slot, route, etc.
After the auction has ended, the game would calculate points for each airline based on their offer and CI and perhaps something more. The slot would then be given to the airline that got the most points. And the airline would be required to use that slot as they offered for a given time, so that they couldn't cheat the system. If they didn't use the slot like they claimed, it would be given to the airline with second highest score.
I don't know how hard it would be to code this, but the point calculation should be pretty simple, with different weight on different items like route length, seat capacity, and those then added together.