The flight is dated Saturday, August 7, 2004.
edit: I see, the FAA is scheduling AMT flights but the one you linked to had already been cancelled when I looked. They import a base schedule from OAG and are known to have a number of issues they don’t regard as problems with the import.
AMT is Mexican Navy. AMT is the first part of their registration, but as Amtran is still in the system then it picks them up. Quite useful!