17- HOU-MSY Southwest, MSY-XXX unknown, XXX-FPO Bahamasair; XXX isn't in FL or GA; the missing airline isn't CO, DL, or US
I don't think UP had any other services to the U.S., so that seems to imply XXX = Nassau/NAS ... which creates *massive* confusion because I can't think of anyone who would have run a 737 MSY-NAS
wild guess: Turks & Caicos Airways, with the flight continuing to Providenciales/PLS