Bomb man didn't have a chance: passengers

The man who threatened to blow up a flight out of Melbourne "didn't have a chance" against the group of passengers who jumped on him.

Scottish man Robert Macdonald was in Australia to visit his grandkids and responded when a flight attendant called for help on Malaysia Airlines flight MH128 late on Wednesday night.

"The girl called for help... (it's) the thing you do," he told reporters on Thursday.

"He had four or five us, quite big guys, he didn't have a chance. (We put) knees on him, hands on him."

Mr Macdonald said the stewards tied the man up with a seat belt and then used plastic wire to restrain his hands.

"I couldn't see if he was drunk but his eyes were glazed, we had him down and his eyes were just staring and glassed. I think he was on drugs," he said.

Mr Macdonald lives in Milton Keynes in England and was travelling with his wife to see their daughter and grandkids.

"I'd do it again. I just had to get on and help," he said.

A 25-year-old Sri Lankan national living in Dandenong on a student visa has been arrested and is speaking to police over the incident.