I don't like it that when a plane is off the ground (you notice it by the shadow it's casting), it still registers as a collision when it flies over a plane that has just landed.
Maybe make the solution at the end of the manual a tutorial level, so everything is a bit more clear. Other than that, the game is good actually. Actually programming takes some getting used to.
I would add a "refresh stock" button or something. I mean, now the game just pauses and ramping everything up to 25 is a bit tedious. Maybe also add an upgrade to be able to carry more thing at once. Otherwise very fun and good game :)
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