Once of the few 'realistic' aspects of AE that I think would be a helpful implementation is on-time flights. This is something which could be gauged on how hard you're pushing your fleet, your staff happiness, union satisfaction, even the airports that you're using and how busy you are and what facilities you have at that airport could all play into this.
e.g. using a jetway instead of aircraft stairs may help keep things on-time...but only if your aircraft has built-in stairs. Aircraft without these may actually take a time penalty by not using a jetway...if that all makes sense as an example.