A Sydney terror accused allegedly sent his unwitting brother to his death with a bomb in his check-in luggage that would blow up an Etihad flight.

But the luggage was never checked in after the passenger was queried about the bag’s weight at the check-in counter for the July 15 flight, police said.

Australian Federal Police Deputy Commissioner Michael Phelan confirmed on Friday that Khaled Khayat, 49, and Mahmoud Khayat, 32, were last night charged with terror offences, after having allegedly planned “one of the most sophisticated terror plots attempted on Australian soil”.

They face a maximum penalty of life imprisonment.

The two men did not appear at Sydney’s Parramatta Local Court on Friday morning, with their lawyer Michael Coroneos saying he did not require the men to be shown on the audio-visual link screen in court.

The case was adjourned until November 16.

Police will allege that Khaled Khayat carried the device to Sydney’s international airport in the hope of putting it on the plane in “checked luggage”.

Mr Phelan said that at no point did the men’s improvised explosive device (IED) breach airport security.

“It did not get through security,” he told reporters.

Police further alleged the parts for the IED came from a senior Islamic State associate in Turkey.

Mr Phelan alleged that the IS member had sent the components to Australia by air cargo where it was assembled into an explosive device.

But authorities are confident they had now found “every single component of that IED”.

Mr Phelan added: “One of the two gentlemen charged, the brother we’re alleging is a senior member of ISIL in Syria and he indeed introduced another person, who we call the controller, to one of the people that has been charged.”

After the aborted attempt on July 15, the IED was disassembled by one of the accused, the police will allege.

The brother left Australia on the flight and remains overseas.

One of the accused and the IS controller then discussed how to create a chemical device with the potential to release colourless toxic gas, hydrogen sulfide.

“It was designed to release the highly toxic hydrogen sulfide,” Mr Phelan said.

But police noted the chemical plot was only “hypothetical”, and the alleged terrorists were “a long way from having a functional device”.

Another man, Khaled Merhi, remains in police custody under special anti-terror laws, while police investigations continue. Mr Merhi can be detained until the weekend under the current ruling.

A fourth man and the brother of Mr Merhi, Abdul Merhi, 50, was released on Tuesday from police custody without charge. All four of the men are related through marriage.

Mr Phelan confirmed the aborted July 15 attempt involved a high-end explosive being concealed in a meat grinder.

“If it hadn’t been for the great work of our intelligence agencies and law enforcement over a very quick period of time then we could well have a catastrophic event in this country.”

– with AAP