A trigger action is a simple SQL statement.
CREATE TRIGGER . . . DELETE FROM flightavailability WHERE flight_id IN (SELECT flight_id FROM flightavailability WHERE YEAR(flight_date) < 2005);)
A trigger action does have some limitations, though; for example, it cannot contain dynamic parameters or alter the table on which the trigger is defined. See "TriggerAction" in the Java DB Reference Manual for details.