Airport_mapping is a project mainly written in PHP, it's free.
This sample script will display the IATA airport codes, which have same names as PHP internal function matches "/^[a-z]{3}$/".
The result is following:
$ php airports.php CHR : Chateauroux airport at Chateauroux, FRANCE ORD : O'Hare International airport at Chicago, UNITED STATES ABS : Abu Simbel airport at Abu Simbel, EGYPT SIN : Changi airport at Singapore, SINGAPORE COS : Colorado Springs Metropolitan Area airport at Colorado Springs, UNITED STATES TAN : Tangalooma airport at Tangalooma, NORWAY POW : Portoroz airport at Portoroz, SLOVENIA EXP : not defined LOG : Longview airport at Longview, UNITED STATES DIR : Aba Tenna D Yilma airport at Dire Dawa, ETHIOPIA END : Vance AFB airport at Enid, UNITED STATES KEY : Kericho airport at Kericho, KENYA MIN : Minnipa airport at Minnipa, AUSTRALIA MAX : Matam airport at Matam, SENEGAL POS : Piarco airport at Port Of Spain, TRINIDAD AND TOBAGO $