An alert which caused a US-bound aircraft to return to Sydney on Tuesday may have been triggered by a misunderstanding rather than a hoax.
A flight bound for Los Angeles turned back after a note reading "B-O-B" was found on a sick bag in a toilet.
The United Airlines captain decided the note could have meant "bomb on board".
But airline workers said the acronym was also commonly used to mean "best on board", referring to a particularly attractive passenger.
"The innocent meaning of the acronym within cabin crew... can mean
'best on board'," Michael Mijatov, from the Australian Flight Attendants Association, told ABC radio.
Correspondents said the letters could have other meanings too, as well as spelling a man's name.
The flight, carrying 246 passengers, left for Los Angeles on Wednesday with no further delays.
Transport Minister John Anderson defended the pilot's decision to turn back.
"In circumstances like that I don't think either you, I or any
of our listeners would be too keen to pass judgement... In my view
the pilot was right not to run risks," he told Channel Nine.
Police said investigations would continue to try and find the person who wrote the note.
"Someone has been irresponsible at least, and
horrendously selfish and stupid at worst, and every effort will be
made to find the person responsible," Mr Anderson said.
The scare follows mounting security concerns in Australia.
Over the weekend an organisation calling itself the Islamic Tawhid group and the European branch of al-Qaeda threatened to attack Australia with "columns of rigged cars" unless it withdrew its troops from Iraq.
And there has been alarm at a number of recent security breaches at Australia's airports, including an alert at Brisbane airport in May, when a passenger wandered into a sterile zone without passing through security.