Two brothers were handed lengthy jail terms in Australia Tuesday for plotting to bring down a Sydney to Abu Dhabi flight with a bomb carried in a meat grinder by their unwitting brother.

Australian-Lebanese brothers Khaled and Mahmoud Khayat were convicted of terrorism offences for trying to bomb an Etihad Airways passenger jet in July 2017 under instructions from the Islamic State group.

Khaled was sentenced to 40 years with a minimum of 30 years without parole, while Mahmoud received 36 years' jail time and ordered to serve at least 27.

The improvised device was to be smuggled inside the luggage of a third, unwitting brother.

A fourth brother, who is said to have fought with the Islamic State in Syria, is accused of directing the plot from overseas.

The plotters disapproved of their brother "because he drank, went clubbing, gambled and was gay, which they regarded as bringing shame on the family", judge Christine Adamson noted.

The plan was aborted at the airport when the plotters decided it was too risky to get through customs after airline staff said their bags were overweight.

In handing down her sentence, Adamson said despite no one being killed, the offenders had succeeded in "creating terror" because the public was made aware of the plot.

"The conspiracy to which both offenders were parties plainly envisaged that a large number of people would be killed," she said.