Leaving the various PC trolls aside for a moment (notice to all: don't feed the trolls!).
The last sentence in this Reuters report is interesting, as it pretty clearly states that AirAsia had, in fact, the permission to fly on the day.
Excerpted quote:
A joint statement from Singapore's civil aviation authority (CAAS) and Changi Airport Group said that AirAsia had the necessary approvals to operate a daily flight between Surabaya and Singapore.
Full article here:
Weather frustrates divers as more AirAsia wreckage found | Reuters