Airport City Hints for iPhone/iPad
To rotate the runways go to the bottom of the screen where the icons are located (shop, plane, box, treasure, people, arrow and gift) and tap the arrow icon, then just click on the orange and green arrows.
Don't forget to check back for a daily reward.
Although it costs try to expand your land whenever possible so you can build a bigger town/airport to generate more cash. The more runways you have, the more planes will be able to take off and land at any given time but keep in mind though that each plane needs it's own hangar and that costs.
Invest in some Power Plants to generate more electricity because the bigger your town/airport gets the more electricity you will need.