Build a 2000 meter runway for big planes, and then build at least two terminals. When your airport rating is high enough, go to contracts, and then go to refueling. There you must choose the highest refueling company (2 stars or more). Next go to the catering section in the contracts group and do the same. Now you should have more airline contract offers that have big planes!
This video should give a good example: http://www.youtube.com/watch?v=sJDF0loNd74