I think if's required to establish some slot distribution system.
I'm working at Beijing Airport, we do have slot restriction according to the type of aircraft. In fact, scheduled flight operated by light aircraft is not allowed in PEK, and small private jet has only 2 slots per hour. But in the game, to ban light aircraft is impossible, so we should put restrictions on those operator.
First, certain categories of aircraft must be decided, my idea is:
Light-I :Cessnas,LET410s.
Light-II:CRJ200/700s, ERJ135s, DH4s, ATRs.
Medium: Airbus 320s, Boeing 737s, EMB190s, CRJ900/NGs
Heavy: All wide-body aircraft included.
New York JFK as example. There're 11 slots pre 5 minutes, and they can be categorized to four groups as follow:
1——Light-I
2——Light-II
6——Medium
2——Heavy
Geneva as example. There're 5 slots pre 5 minutes.
1——Light-I
1——Light-II
2——Medium
1——Heavy
And those slots are upward compatible, which means a 747 can uses slottime for light or medium a/c, but a Cessna can never use a slottime for bigger plane.
The benefit is that when the game are in later phrase, transcontinental flights could be easy to arrange because the big airports have some slots reserved for them, instead of being stuck in repetitive regional flights. For long-term design, those small plane operators could pay handsome money to upgrade their slot category.