You are getting events from the December 3rd because 03-DEC-12
gets interpreted as 2012-12-03T00:00:00
and an event 10 hours after midnight does match.
If you want events starting the following day, use
SELECT *
FROM flight
WHERE FLIGHTDATE >= DATE '2012-12-04'
-- or FLIGHTDATE >= (DATE '2012-12-03') + 1
You could also truncate the datetime to a date using the TRUNC
function, but this may make the query non-sargable:
SELECT *
FROM flight
WHERE TRUNC(FLIGHTDATE) > TO_DATE('03-DEC-12', 'DD-MON-YY')