What is your suggestion?
I have found than when airports are in very high levels, I have lots of Wollars, but limited crew, and contract slots.
How would it work in the game?
As an airport levels up, there would be options to use Wollars to buy contract slots.
Why is this a good idea?
Because this game is designed to be able to be played without spending any real money, I think we should be able to use the in game currency to buy features or additions to the airports
I have to disagree with you on this. There are already enough options to purchase contract slots for in-game currency (SP, GP). I would like to see the wait time between the purchases to go back to just 1 day instead of the 2 it is now. Here’s a thought, in the late game (like, really late), you’re going to get hundreds of thousands of silver planes, so what are you supposed to do with them if contract slots became available for wollars? There aren’t that many ways to spend them and contract slots are quite an important feature to the economy.
We need to be able to spend SP on additional slots to a destination. Also a lower timer would be great. Currently sitting on 7 mil SP…
At the same time, what are you supposed to do late game with millions of wollars? I have over 12m wollars at my maxed out lhr but limited contract slots to spend them on. Also as the OP said being able to buy more crew especially for an airport like lej would be useful as well. Maybe in order for it to not break the economy of the game by allowing players to skip progression this feature can only be unlocked one you reach 3 stars on an airport.
Idk, buy a ton of Concordes I guess? 
But jokes aside, that’s actually a really good point, but then it would still raise the question of: 1. How long of a cooldown period to give for this? (it can’t be too game-breaking, but it could also use up a lot of those wollars, so where’s the balance?), and 2. How much would it cost? It can’t be too little, but it also can’t be too much to only be used by a handful of players. Plus, even if the right balance were to be found, wouldn’t it do basically the same thing as if the slots for SP purchases had their cooldown shortened? If you’re already at such a late-game stage, you should have plenty of SPs to “throw away”, so would it really matter if you spend wollars instead of SPs?
I think so. When new airports come out, you would need SPs there (likely) and still have wollars to use at older airports.
I get your point, but wouldn’t that be better for the economy? That’s what it’s all about, having to decide what to spend your money (in this case SPs) on is the whole point of economy as a concept. You either get one, the other, or a part of both. I think you’re already spoiled for choice this way.
That’s a good point, but when an airport is at a high level, you could have a huge amount of wollars, so what are we supposed to do with those? Anyway, this is just an idea. Who knows if it will be added.