---

So that gave Dubyah and Tony quite a bit of leeway for invading Iraq, right?

---

---

IED does not imply professional or military design

---

---

---

---

---

---

Flight release form ? If official , opens up a whole new area of investigation

---

---

---

---

The son of a man arrested in Sydney over an alleged plot to bring down an aeroplane with a bomb or deadly gases studied aviation management and mixes with a network of pilots and airline workers, it can be revealed.

The revelation comes as sources confirmed to Fairfax Media that the Sydney cell behind the alleged plot were talking to foreign fighters in Syria in communications that were picked up by allied intelligence agencies.

The son of one of the men arrested was reportedly studying aviation management in NSW.

It is understood that British and US spies fed the information to Australia, triggering police to bring forward a planned operation by launching dramatic raids in Surry Hills, Punchbowl, Wiley Park and Lakemba on Saturday evening.

Four men – two middle-aged fathers, one adult son and a relative in his 30s – remain in custody at the Sydney Police Centre on suspicion of attempting to build an improvised explosive device that they could smuggle onto a plane, believed to be a commercial flight to Dubai.

The alleged plot, described by police as sophisticated and elaborate, was allegedly hatched with help from Islamic State operatives in Syria.

On Sunday night, the AFP successfully applied to a court to detain the men for up to a week without charge.

Police have seized several items from four homes, including a kitchen meat mincer possibly intended to hold the bomb.

Precursor materials were found that could have been mixed to make either an explosive device or a noxious gas to incapacitate those on a plane, it's understood.

Khaled Merhi, aged in his 50s, was arrested in Surry Hills and his son, Abdul Merhi, was arrested in Punchbowl.

Khaled Khayat, also in his 50s, was arrested in Wiley Park and a relative, Mahmoud Khayat, was arrested in Lakemba. The four are related through marriage.

One of Khaled Khayat's sons, who has not been arrested and is not facing charges, studied aviation management at UNSW.

Several photos on online profiles show he socialises with alumni who have gone on to become international pilots, airline managers, airline network analysts and air traffic controllers.

Fairfax Media is not suggesting he is involved in the allegations and police don't believe the group infiltrated any internal airport systems or staff.

In one online post from 2015, the son described his father as "the best man on the planet".

Bomb squad officers and heavily armed police searched a unit on Sproule Street, Lakemba, following the arrest of four men.

"He has been my hero and inspiration for all my life and been there for me through all the ups and downs. Always being wise and full of heart he is the man that I aim to be everyday of my life," he wrote.

On Monday, Australian Federal Police Commissioner Andrew Colvin said the information received by police had no "specificity on what was to be attacked" or "when it was to be attacked".

Bomb squad officers were among police who raided a terrace house in Surry Hills on Saturday night.

He declined to comment on the overseas tip-off.

"I think the important point here is the intelligence was received, police and our security partners have acted very quickly to stop and disrupt another attempted attack in this country," he told reporters in Brisbane.

Jacinta Collins, a counter-terrorism expert with the Australian Strategic Policy Institute, said bringing down a plane or killing large numbers of people would have been a significant technical challenge.

"The things that would make the most impact are almost impossible to get onto planes these days," she said.

But any kind of attack on a plane would get the attention and headlines terrorists crave, she said.

"You don't need to necessarily kill or injure many people to get the attention. Terrorists do look for something that is a vulnerability to demonstrate their power and get a headline."

Rodger Shanahan, a terrorism specialist with the Lowy Institute, said the group might have had multiple targets and back-up plans beyond a plane attack.

He said police were right to move when they did based on what they had gleaned about the alleged intent, but it remained to be seen whether their capabilities matched their ambition.

He said the involvement of overseas intelligence agencies demonstrated the benefit of sharing information so that even suspects who weren't on a current radar in Australia could be picked up.

"You need to have your net cast as widely as possible. That's why all these strong relationships we have with overseas partners … is really, really vital. You can't do everything yourself so you need close partners."

Greg Barton, an expert from Deakin University, said dispersing a sulphur-based gas on a plane "doesn't make any sense at all" because even potent gasses such as the nerve agent sarin were hard to "weaponise".

He said the alleged targeting of a plane was "quite a threshold that has been crossed" in Australia.

The counter-terrorism operation forced authorities to implement enhanced security arrangements at all major Australian airports including extra screening and baggage checks. It led to long delays at Sydney Airport on Monday.

Officers in protective gear continued searching homes in Lakemba and Surry Hills on Monday, digging up yards and going through garbage bins.

---

---

High-grade military explosives used to build the bomb were sent by air cargo from Turkey as part of a plot "inspired and directed" by the militant Islamic State group, police Deputy Commissioner National Security Michael Phelan said. ...

"This is one of the most sophisticated plots that has ever been attempted on Australian soil," Phelan said. ...

Since police revealed details of the scheme, security experts said it exposed weaknesses in air cargo screening, particularly in Turkey, where intelligence agencies have been weakened by a government purge in the wake of last year's failed coup.

"Islamic State is now positioned in Turkey such that it can send military-grade explosive via cargo flights out of Turkey around the world," said Deakin University's Barton. "Now presumably Sydney is not a one-off and they are going to try this elsewhere and that's a level of risk that we hadn't thought of before."

---

---

---

---

Having picked an international flight as their target, the men were forced into a last-minute change of plans when the baggage wasn't allowed on board.

But Australian authorities were only alerted by overseas intelligence agencies when the alleged conspiracy was revived.

---