Australia has been handed control of the southern Indian Ocean search for missing jet MH370, after investigators revealed someone broadcast "good night" from the cockpit after the plane's tracking systems were switched off.

Prime Minister Tony Abbott told Question Time today that along with assuming responsibility for the "southern vector" search, Australia has also committed more resources to the operation.

Investigators believe the plane could have flown in one of two different directions after its tracking systems were turned off - one north-west into Asia and another path south-west into the Indian Ocean.

They say someone had broadcast the informal sign-off "all right, good night" after the plane's tracking systems had been disabled, a revelation that could further heighten suspicions of hijacking or sabotage.

"The answer to your question is yes, it was disabled before," Malaysia's acting transport minister Hishammuddin Hussein told reporters yesterday when asked if the ACARS system - a maintenance computer that sends back data on the plane's status - had been deactivated before the voice sign-off.

The hand-off went against standard radio procedures, which would have called for the pilot to read back instructions for contacting the next control centre and include the aircraft's call sign, said Hugh Dibley, a former British Airways pilot and a Fellow of the Royal Aeronautical Society.

Investigators are likely to examine the recording for any signs of psychological stress and to determine the speaker's identity to confirm whether the flight deck had been taken over by hijackers or the pilot himself was involved, he said.

Malaysian investigators are trawling through the backgrounds of the pilots, crew and ground staff who worked on the missing Boeing 777-200ER for clues as to why someone on board flew it perhaps thousands of miles off course.

Background checks of the 239 passengers have drawn a blank but not every country whose nationals were on board has responded to requests for information, police chief Khalid Abu Bakar said.

No trace of the plane has been found more than a week after it vanished but investigators believe it was diverted by someone with deep knowledge of the plane and commercial navigation.

The search for the missing plane now involves 26 countries and covers a vast area from central Asia to the southern Indian Ocean.

China, France and the United States have all been asked for more satellite data and the call has also gone out for more ships and planes.

The Government initially provided two P-3 Orion aircraft to the search, and has promised another two Orions will be available for patrol within 24 hours.

'Most botched aircraft investigation in history'

Foreign Minister Julie Bishop told Question Time that Australia would continue to hand all of its defence intelligence to Malaysian authorities, who have overall responsibility for the operation.

But a senior aviation writer told The World Today that governments should be telling the Malaysian authorities they are not competent to run the investigation.

Editor of website airlineratings.com, Geoffrey Thomas, says the search for the missing Malaysian Airlines plane is "one of the most botched aircraft investigations in modern history".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 4 minutes 26 seconds 4 m 26 s Missing aircraft investigation botched: expert Download 2 MB

"Unfortunately we have not been told by the Malaysians in a timely fashion about the shutting off of the ACARS, the shutting off of the transponder, the plane going to the west," he said.

"Millions of dollars has been wasted, days have been wasted searching in the wrong area. I think this is without doubt one of the most botched aircraft investigations in modern history."

Thomas says Malaysian authorities have known the vital information since the plane went missing on March 8 and it is "inexcusable" that information was not revealed on the day.

He says if the information had been released earlier it would have focused the search on a narrower area.

"Look, absolutely. I mean, for instance, the whole 10 or 15 nations wouldn't have wasted time looking in the South China Sea," he said.

"They would have been looking over in the Indian Ocean, west of Malaysia, not east of Malaysia.

"Critical time has been lost here and it's just inexcusable and it's dashed the hopes of the relatives and given them a torturous seven days of theory, then no theory, then counter-theory. All of that could have been dashed and we could have been looking in the right place.

"You'd have to say, without further clarification, the Malaysian air investigation, the Department of Civil Aviation in Malaysia is to blame. They're running the investigation.

"It's not Malaysian Airlines' fault. It's the fault of the authorities and the military in Malaysia as well."

Thomas says that if the plane flew into the middle of the Indian Ocean then the chances of finding it are "remote".

"This aeroplane may join a long list of planes that have disappeared over the last century with no trace whatsoever," he said.

Defence Minister David Johnston says he is satisfied with the communications from Malaysian authorities.

"I am satisfied with them. I think they're as perplexed as we are and, you know, I've seen an absolute parade of experts on television stations pontificating and hypothesising about what has happened to this aircraft," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 9 seconds 3 m 9 s Search may continue for weeks: Defence Minister Download 1.4 MB

"It is most mysterious."

Mr Johnston says he is prepared for Australian teams to keep searching for weeks for the missing Malaysian jet carrying 239 people.

"I think we are locked in to do what we can to assist the Malaysians as best we can for as long as it takes," he said.

"That doesn't mean we will be there for the next 12 months but nevertheless we've got to really make a big effort in these next two or three weeks, certainly, to get to the bottom of what has happened here."

Pilot's home searched

On Saturday, police special branch officers searched the homes of the flight's captain, 53-year-old Zaharie Ahmad Shah, and first officer, 27-year-old Fariq Abdul Hamid, in middle-class suburbs of Kuala Lumpur close to the international airport.

Posts on the captain's Facebook page suggest he was a politically active opponent of the coalition that has ruled Malaysia for the 57 years since independence.

A day before the plane vanished, Malaysian opposition leader Anwar Ibrahim was convicted of sodomy and sentenced to five years in prison, in a ruling his supporters and international human rights groups say was politically influenced.

An experienced pilot, Captain Zaharie has been described by current and former co-workers as a flying enthusiast who spent his days off operating a life-sized flight simulator he had set up at home.

A senior police official says the flight simulator programs have been closely examined, adding they appeared to be normal ones that allow users to practise flying and landing in different conditions.

A second senior police official has told Reuters investigators have found no links between Captain Zaharie, a father of three grown-up children and a grandfather, and any militant group.

The two corridors that might have been flown by Malaysia Airlines flight MH370. ( ABC TV )

ABC/Reuters