Maybe some personnel management, getting good pilots you have to pay more, payroll staff are needed for large companies otherwise they'll embezel funds, etc...
Also potential disaster mechanics, if a plane is used too much increase the percentage chance of a "disaster" event, which would kill/injure/disappear the occupants of a flight, this creates a short term plummet in sales, and a medium term negative modifier on willingness to fly with that airline
- jaybee