03/08/2017 3:58 PM AEST | Updated 03/08/2017 4:03 PM AEST

Airport Delays Should Start To Ease As Terror Threat 'Disrupted And Contained'

The aviation terrorism threat has been lowered to 'possible'.

Andrew Meares/Fairfax
Prime Minister Malcolm Turnbull: 'The plot that was uncovered to bring down a plane has been disrupted and contained.'

CANBERRA -- Terror-related aviation delays for travellers should start too ease soon across Australia with the announcement that the threat from an alleged Islamist extremist terrorist plot to bring down a plane has been "disrupted and contained".

The Director-General of the domestic spy agency ASIO has advised that threat level to aviation has now been downgraded from "probable" to "possible" after being raised in response to last week's terror raids across Sydney.

Three men are being held in custody under special provisions of the Crimes Act. They have not been charged. A 50-year-old man was released on Wednesday without charge.

Prime Minister Malcolm Turnbull told reporters in Perth on Thursday that investigations had uncovered evidence "very successfully" and he had been told to expect charges to be laid.

"Investigations have proceeded very well in terms of uncovering evidence. And they've got very strong evidence. And I should expect charges to be laid in due course," Turnbull said.

The national terrorism threat level has remained at 'probable' throughout the recent counter terror activity, but the specific advice on aviation had been raised last week.

"The Director-General of ASIO has advised the threat to aviation will be restored to the level it was a week ago," Turnbull told reporters in Perth.

At the same time, enhanced security measures will continue at airports, but be modified to reduce delays.

"Some will be obvious to travellers and others will not," the Prime Minister said. "But they will be modified in a way that will cause less delays to the travelling public."

So back to normal, just everyday, non-terror related delays?

"You should expect, travellers should expect to receive advice from their airlines within the next 24 hours that the time, in arrival times, that's to say arriving at the airport before a flight, will be restored to those that previously applied," Turnbull explained.

"You know, which was an hour for domestic, two hours for international. But some airlines differ."

As ever, travellers are being urged to check with their airlines.