Idea for additional realism:
Not only implement “slots” in terms of “runway operations”, but also “gates” in terms of parallel handling of aircrafts.
Example from a small airport in Germany: You can fly 4 planes per 5 mins into MGL, but MGL can only handle 6 planes in parallel (see the parking positions in google maps). More than 6 planes handled heavily increases turn around time!
It is not easy to implement, it would act like “slots after slots”. Land at 8:00, but the next handling is available from 8:15 on. Or change from “runway slots” to “handling slots” that are used for the time of turnaround. The runway slots should fit to those from handling in real life? This would increase the use of terminals: you can increase the handling!
Edit: just found Redefinition of airport handling capacities, maybe revamp this idea, but make it simpler. No “gates sizes”, but maybe only in numbers of “passengers handled per 5 min” similar to the slots. Given e.g. a 15 min “deboarding” (defined at first by the plane) of a 150 pax plane takes 30 pass/5min of capacity to get to the planes boarding/deboarding-limit. As for the example MGL, they could maybe have a capacity of 15pass/5min (20 seconds each, only one check in agent!). So a A320 could still land, you can still land more planes, but ONE such plane will block the entire airport for 10x5 mins = 50 mins instead of 3x5min = 15 mins.
Data: add “#pax” to the 5min-slots, limited by the max pass / 5min, filling it up beginning at “deboarding” / “boarding” time from the shedule until all pax are accounted for.
Visualisation: similar to the slots, but “% of pass handling” visualized (in addition: “# of pass available / 5 min”).
Edit 2:
The “gate size” could be simulated by this too, but only slightly:
Give a “malus” if the capacity of the airport is less than the capacity needed by the plane. This neglects the size of the gate, but still gives a number (15/5min equals ~1 narrowbody…).