I just realised that especially for newly started airlines, predicting how much money you will make in a month is extremely tough, as the airline is very volatile indeed. So, the following would be requested:
A function to predict the amount of profit/loss you might make in a month. This will calculate based on current load factors on routes, predicting end of month revenues and then removing expected costs. This should not be used in a month of great expansion.
I would understand if this can't be implemented as what is outlined would probably be quite demanding to code, and also, it may begin to lose functionality as the player's airline becomes more stable. However, it would still be a pretty good idea, if implemented correctly.