Contracts: By accepting a contract we can recieve additional revenue (say +10% as an example) for carrying additional cargo on our passengers flights. For example, I can accept a contract at INN to send X amount of mail to various different airports across the UK, such as MAN, LHR, LGW and EMA. This mail will generate additional income on all flights to the UK. Once X amount of mail has been delivered, the contract will be complete giving the player gold planes as a reward.
Charter flights: We can send our aircraft on routes that wouldn’t normally exist from a certain airport, such as having an aircraft chartered by a Cruise Line to send a 757 from INN - JFK and back. Because the aircraft is doing a flight for another firm (Cruise Line, Tour Operator, event etc), the flights will be one offs (or seasonal). Players will be rewarded with gold planes (possibly based upon aircraft category or distance).
This is just something I came up with, and might add a new level of interest into building up fleets. Gives our aircraft something else to do.