DHAKA: Some 25 countries are now involved in a vast search operation for the missing airliner that disappeared over a week ago, Malaysian officials say.

The search area - from central Asia to the southern Indian Ocean - takes in large tracts of land and sea, reports BBC.

An already complex search operation has become even more difficult, Malaysia`s acting transport minister says.

Crew, passengers and ground staff are being investigated after it was confirmed the jet was commandeered.

A former 777 pilot has told me how easy it is to switch off most of the systems that track an aircraft. Most pilots would know how to do it - though traditional radar would still pick up the presence of a plane.

Firstly, most systems, like the transponder, the radio, the ACARS etc, have what is effectively an "off" switch.

Secondly, every electrical system also has a circuit-breaker, a bit like the fuse box in your house. The pilot has a panel of hundreds of buttons above his or her head; if they pull the right one, then the system switches off. The breakers are essential to isolate electrical systems if they overheat or catch fire.

But if you switch anything off, an orange warning light appears on a screen in front of the crew. So it is highly unlikely one could do it without the other noticing.

And the pilot may still not know about every system the aircraft has that talks to satellites - which could explain how this aircraft was sending out pings despite everything else being switched off.

The idea of hacking into an aircraft`s systems has also been mooted, but I am told this is far less likely on an aeroplane such as this and also that the manufacturers have put in a lot of work to stop this happening.

One final thing: if this aircraft flew low over land, and people on board knew there was a problem, why did no-one try to make a phone call?

Investigators are trying to obtain more radar and satellite data from any of the countries that Malaysia Airlines flight MH370 may have passed over, with its 239 crew and passengers.

The leaders of several Asian countries have been briefed by the Malaysia government in what acting Transport Minister Hishammuddin Hussein has described as a new phase of the search.

"From focusing mainly on shallow seas, we are now looking at large tracts of land, crossing 11 countries, as well as deep and remote oceans," he said at a news conference.

Malaysian officials are contacting countries including Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, Pakistan, Bangladesh, India, China, Myanmar, Laos, Vietnam, Thailand, Indonesia, Australia and France.

They are also asking countries to provide assistance in the search for the plane, including satellite data and analysis, ground-search capabilities, and maritime and air assets.

After checking their radar recordings, Pakistani civil aviation officials said they had found no sign of the missing jet.

Malaysian national police chief Gen Khalid Abu Bakar said background checks had been requested on all passengers aboard the plane, but that so far nothing suspicious had been reported - though some intelligence agencies still had to respond.

The police are also reportedly looking at the family life and psychological state of the plane`s pilot, Zaharie Shah, and co-pilot Fariq Abdul Hamid, and searched their homes on Saturday.

The two men had not asked to fly together, Mr Hishammuddin confirmed at the news conference.

Officers spoke to relatives of the pilot and experts are examining the pilot`s personal flight simulator. Police have visited his house for a second day.

Those who know Mr Zaharie, 53, insist he is a normal family man, reports the BBC`s Jonah Fisher in Kuala Lumpur.

With 18,000 hours of flying experience, he is a self-confessed "aviation geek" and proudly posted pictures online of the flight simulator he built at home.

As well as the crew and passengers, police are investigating the engineers and other ground staff who may have had contact with the aircraft before take-off.

It has also emerged that a team from British telecommunications company Inmarsat team arrived on Saturday in Malaysia.

An Inmarsat satellite is said have continued receiving signals from flight MH370 at least five hours after the plane was reported lost.

A team of French investigators is to travel to Malaysia on Monday to help with the search, the French transport ministry has said in a statement. They will join members of the US National Transportation Safety Board already in Malaysia.

BDST: 0904 HRS, MAR 17, 2014