Have the game patched to the latest version. Use a text editor to edit the "airlines" file in the "program filesglobal star softwareairport tycoon 3datadb" directory. Set the value for the "QUALITY" line to "1". All airlines will now be unlocked.
MassDrop - Get Huge Airport
INeedCash - Get 100.000.000 extra money
DoTornado - Invoke Tornado
SetBudget xxx - Get xxx extra money
SetCash xxx - Get xxx extra money
HideGame - Hide Game
ShowGame - Unhide Game