Airline Club

Pardon the vague title, this touches upon a number of things... I generally approached this with the goal of making niches viable and more fluid standings, so newcomers/players outside prime regions can have fun with something that works for them. That said, I realize patson has his own vision and philosophy and these are just based off my own somewhat subjective impressions, so I completely understand if he rejects these ideas

Aircraft selection can be very hit-or-miss - there are breakpoints that make an aircraft become light, medium, large, etc, which can have significant effects on how competitive they are, as the slot fee depends on these brackets. Moreover, range is also binary - either your aircraft can serve the route, or it can't. Then there's turnaround times, max speeds within certain range brackets, etc. As a result, there are many aircraft that are less competitive than they might otherwise be - for example, hardly anybody uses the Airbus A319 because it barely misses the cutoff to be considered a Regional jet, while the Boeing 787-8 Dreamliner is a popular option because it maxes out the Medium bracket.

To this, I would suggest eliminating the categories entirely and replacing category-dependent things with capacity scaling - this will smooth out aircraft selection and avoid aforementioned funny situations. Since the aircraft supplier discount is based on these categories, perhaps maintenance, training, and operational costs might be based off the number of aircraft families an airline has. This would allow up-and-coming airlines the ability to specialize, while larger, more established airlines would have to make strategic decisions about where and what they do. The current limit for model of aircraft your airline can have is a little dissatisfying since it's locked behind reputation - there's often not much you can do besides sit and wait for reputation to increase, especially if you're maxed out and don't have a free model to gradually transition your fleet.

One other factor missing is that currently aircraft are more fuel-efficient maxing out their range, as the takeoff/landing portions consume more fuel and range brackets limit max speed: the extra distance averages out towards cruise fuel consumption. This, however, doesn't factor in that aircraft flying longer routes need to carry more fuel on takeoff (which translates into more weight/less fuel efficiency), so the fuel-efficient optimum IRL is a "medium" distance, less than the aircraft maximum. The fact that long hauls are more efficient than shorter flights, given the same aircraft, makes point-to-point flights more attractive. This mostly benefits the large, rich cities with attractors and makes regional hubs less viable - after all, why connect to a regional hub when I can connect directly to LHR/JFK/etc?

I understand that the Staff system was added in part to mitigate this by forcing airlines to carefully choose where they connect, but I'd argue the effect of limiting frequency/routes makes these cities more important - if I've got limited routes, I'm going to prioritize the important, well-connected cities with guaranteed volume over the less connected ones. Perhaps this might change as the routes get more saturated, but right now it seems like performance is very dependent on city charms and not so much geography. This is doubly true when factoring in higher-capacity planes are less reliant on Staff, so it's more rewarding to connect large hubs to each other than underserved, smaller cities.

Lastly, a small change I'd suggest is scaling aircraft condition reduction with utilization rate. I think this makes sense, since the more you cycle the aircraft, the more wear & tear they get. Right now, any usage at all reduces condition at the same rate.