Slot Based Contracts
The idea is that when signing a contract with an airline, the airline purchases a number of daily slots. These slots cost more or less depending on demand (i.e. the time of day) and airport rating.
A slot involves a time frame to land, a time frame to take off as well as an available gate. For Airport CEO, I envision a system where runways have a limited number of slots available per hour. For example, runway with small ATC can handle 6 take offs and landings per hour (3 slots per hour), a medium ATC can handle 10 take off and landings per hour (5 slots per hour), and a large ATC a runway can handle 12 per take off and landings per hour (6 slots per hour).
An airport with one medium gate (3 hour turnaround), one runway and small ATC tower operating from 6am to 6pm (daytime hours) could handle four flights per day,so would have four slots per day available. The number here is limited by the number of gates.
An airport with one medium gate (3 hour turnaround), one runway and small ATC tower operating 24 hours per day could handle eight flights per day,so would have eight slots per day available. The number here is limited by the number of gates.
An airport with 10 medium gate (3 hour turnaround), one runway and small ATC tower could handle 72 flights per 24 hours, so would have 72 slots available. The number here is limited by runway capacity (gate capacity is 80 per day). Adding a medium tower or adding another runway would raise the runway capacity.
Each slot is unique. For example, once the 8:00 am arrival slot has been sold to an airline, it is no longer available, unless the airline sells it, or returns it to the airport. The next available slot would be 8:10 am (with a small tower)
Why it should be implemented:
This should be implemented to increase the realism and add to the game play. The number of slots per day or per hour are not realistic but reflect the in-game mechanics and time-scale. This could add a new dimension to the game in that valuable slots become sought after, and can command a high price. It means the airport can charge different rates for slots at different times. This can be simplified to blocks of time, rather than exact times to simplify the code and game play. e.g. Morning peak, midday, afternoon peak, early evening, late evening, night, early morning. The number of slots in each of those larger categories would be limited by number of runways, ATC and gates.
It allows airlines to request slots at their preferred time, which leads to different airport strategies to handle those requests.