] History, rather than geography, solves the puzzle of BNA,
] TYS, GEG, OGG and MCO. The main airport in
] Nashville, Tennessee, was named in honor of Col.
] Harry Berry who helped build it: BNA. Knoxville, also in
] Tennessee, doesn't have a single letter in common
] with its tag of TYS; however, a historian would
] know that the Tyson family donated the land in
] honor of their son killed in World War I.

Some interesting factoids if you fly alot...

Airport Codes: A History and Explanation