Airport generally tend to serve different kind of aircrafts, seeing from what you guys have done so far in the current builds, you already implemented grass and asphalt.
From what I see on your build it looks like carriers ask for contracts. Since different carriers fly different airplane types, wouldn’t it be an idea to implement a minimum requirements for your airport.
Say ‘Airline A’ requires there to be facilities to land light aircraft, possibly DHC-8 or whatever. This would require a short grass runway, there’s no need for certain facilities.
However there’s also airline ‘B’, they require facilities for heavies, A380, B744 etc. This would require a longer runway, with a high MTOW rating, since it’s kinda impossible to land these into a grass runway.
And for example ‘C’ might require facilities for B733, A321 etc.
This would in my opinion add value to the game, A DHC-8 is able to land on a long runway . This would cost some of the runways capacity, which could add to the management off this game.
You could add extra parameters to the game since a heavy has a higher turnaround time, as opposed to a medium or even a light.
I might have read this wrong, but I wouldn’t expect or want airlines to require my airport to support all of its aircraft before flying any flights. It obviously doesn’t work like this in the real world. As an example, British Airways operate A380s and B747s but the airports it serves do not all cater for the jumbos; e.g. Aberdeen would not manage to host an A380 or a B747. That doesn’t stop BA serving the city using narrow body aircraft, which it does many times a day.
What is more sensible is that each individual “contract”/flight has its own requirements and these are obviously self evident. An airline wishing to fly a Cessna into your airport once a day can manage with the basic facilities that your fledging airfield has to offer. That same airline may also have a large fleet of wide body aircraft, but that’s not required for your airport yet so that doesn’t matter. As your airport grows, the heavies may well become important and of course the airlines may start to demand longer runways, wide body stands and so on. This will of course all be self evident - you can’t as you rightly point out land a B747 on a short grass runway and this would in effect not allow you to sign that contract.
Have you considered the airport landing systems installed? As airports developed over time, more elaborate landing guidance systems were required, becoming more expensive to install and maintain. Even large modern airports do not always have them all working at all times. Perhaps started with Non-Directional Beacons, moving later to VOR, Localizer, Back Course approaches to save money, or later implement full ILS landings, and offer having them certified for Category I, II, or III approaches by runway, allowing aircraft with the correct equipment to land even with zero visibility. These later systems would of course be runway specific and have a maintenance price tag, but could help keep airports running during poor weather.
Incidentally, most large airports designate favored take off runways and landing runways to facilitate flow. These runway configurations change based upon prevailing wind, noise abatement considerations, and construction/maintenance on-going. Another thing to consider, depending how realistic you’re going for.