This may be a bit too complex for the game, but what about including seasonal demand. For example, in the winter, there is more demand for flights to skiing destinations etc and in the summer there is a large amount of demand for hot countries etc. This would mean that airlines could have seasonal schedules that vary depending on the time of year.
Search! You may find a lot of answers for your idea.
And very simple AS has no manpower and IMHO not enough money to realize such an idea.
The fluctuation of the AGEX, sort of takes care of this