How about having some skills/stats as a CEO. For instance you could have “charisma,” “negotiation skill,” “stress,” etc.
These could be used to add interesting mechanics to things like airline contracts. Let’s say an airline wants to fly to your airport once a week for X$. If your CEO has good negotiation skills and reputation, he could counter the contract and demand a higher price. And the inverse would apply for negotiating fuel prices.
These skills would develop as the game progresses since the CEO will gain experience. Certain items in the airport could also affect the performance of the CEO. If you have an office with a nice computer, it might increase your negotiation power. If you don’t have a toilet nearby, your CEO might become stressed and make workers stressed an unhappy.
Could also be possible to send the CEO to school for a while to improve certain skills. If you do this, he will go away for a few months and you won’t be able to negotiate contracts and stuff like that in the meantime.