With this cool site I just heard about, you can discover the (sometimes weird, sometimes banal) reason behind each code.
Oh, and FAT = "Fresno Airport Terminal," in case you were wondering. Yeah, I was hoping for something more interesting, too. :)
Making sure you're searching with the right airports
Nowadays, of course, most flight search engines let you do searches by city names, but that has its own challenges. How do you know you're selecting the airport -- or airports -- with the best flight options?
With Google Flights (http://www.google.com/flights), start by typing in a city name, and then optionally click the little + icon next it (see image). You'll then instantly learn about nearby airports and how far they are from the city center... and can add one or more to your search.
I'm a Program Manager working on Google Flights and am always curious to hear your thoughts and questions about the service. :-)
[ Hat tip: My colleague Demian: http://google.com/+DemianCaponi ]