FOUR Australian brothers are facing a death sentence by a Lebanese military court over the “Barbie bomb” plot to explode an A380 plane with 400 on board after it left Sydney airport.

Amer Khayat, his three brothers and another Sydney relative allegedly planned to detonate bombs hidden in a Barbie doll and a meat grinder on a Dubai-bound Etihad flight on July 15 last year.

Hidden in hand luggage, the self-timed bomb inside the Barbie doll was allegedly set to detonate a second bomb inside a meat grinder, killing 400 passengers and crew somewhere over NSW.

It would have been Australia’s most catastrophic terror attack, and the world’s biggest airline disaster in three decades, outstripping the 239 victims who died on MH370 in 2014.

Amer Khayat is the only member of the alleged “Barbie bomb” plot in custody in Lebabon who will likely be hanged or face a firing squad, The Australian reported.

Lebanese military court judge Alaa Katib is preparing to pass the death sentence on the alleged terror cell members, including the brothers and relative in absentia.

Evidence before the military court suggests the alleged bombers were relying on a person who worked at Sydney airport to help the bombs’ path through security checks before departure.

Amer Khayat is currently in a Roumieh facility in east Beirut, one of the world’s most dangerous prisons where suspected Islamic terrorists are held.

Authorities detained Amer Khayat last year after the Sydneysider and dual Australian-Lebanese citizen made several trips to the Lebanese city of Tripoli, where he was to be married at his family home.

But his multiple journeys and quick divorce prompted suspicions.

When authorities questioned him, Amer Khayat allegedly revealed that he had attempted to smuggle the two bombs aboard the flight.

The plot was allegedly made in Raqqa where relatives had been fighting for Islamic state.

A third brother Tareq, an ISIS commander, is hiding in Syria.

Beirut alerted Canberra and in raids across Sydney last July, Amer’s brothers Khaled, 52, and Mahmoud, 32, were arrested and charged with two counts of allegedly planning a terrorist attack.

Israeli intelligence corps claimed its “exclusive intelligence” had helped thwart the alleged attack.

Australian police investigated the fifth alleged “Barbie” plotter, but found there was not enough evidence to charge him.

However, all five men are accused in Lebanon of participating in terrorist activities, being part of a terrorist group and scheming to commit mass murder.

Judge Khatib has recommended Amer and the four alleged bombers outside Lebanon will be tried in Beirut on May 4 and sentenced to death.

The Australian government is unlikely to agree to extradite the two Khayat brothers in custody here to face potential execution in Lebanon.

Amer Khayat reportedly suffers from a mental health condition and is incarcerated in overcrowded conditions in Roumieh where 4000 inmates live in squalid conditions.