China is using satellites and radar to sweep parts of its northern territories in hopes of finding clues to the vanished Malaysia Airlines jetliner, which authorities say appears to have been deliberately flown off its intended route – perhaps a vast distance from it.
The scope of the effort was further underlined by Australia, which on Tuesday sent aircraft to search an area 3,000 kilometres southwest of Perth in the southern Indian Ocean. Some 26 nations have combined their efforts to find MH370 over a band some 8,000 kilometres in length – greater than the return distance between Vancouver and Quebec City. The search grid offshore Australia alone amounts to over 600,000 square kilometres, roughly the size of Manitoba.
"The sheer size of the search area poses a huge challenge," said John Young, general manager of the Australian Maritime Safety Authority. The Australian search is being conducted in co-operation with New Zealand and the United States, which has begun to shift its efforts from ships to long-range aircraft.
Speculation has continued to mount on what might have happened to the aircraft and the 239 people on board, as Malaysian investigators acknowledged they were examining the possibility of pilot suicide among the prodigious array of possibilities. Some families of Chinese passengers aboard the flight have publicly threatened hunger strikes if they don't receive more information.
Some 60 ships and 50 aircraft are involved in the search. China has devoted 21 satellites to the effort.
On Tuesday, China's ambassador to Malaysia said Chinese authorities have cleared their own citizens of involvement in the disappearance of the aircraft. "China has conducted a thorough investigation of all the passengers on the missing Malaysia Airlines flight, and has found no evidence of any destructive behaviour," Ambassador Huang Huikang said, in comments reported by Chinese state television.
Western sources have said background checks on the remaining passengers and crew have similarly come up empty, despite significant attention devoted to searching the background of the two pilots. It seems likely the final radio communication – "all right, good night" – came from the co-pilot, Malaysia Airlines' chief executive has said. Conflicting information from Kuala Lumpur has left it unclear whether that message came before or after the aircraft transponder and other systems went dark.
In Beijing on Tuesday, China's foreign ministry said it has trained its search efforts on its own soil, in response to a request from Malaysian authorities. That search involves both looking at previously-gathered information from radar and satellites, and new efforts to use those tools to look for the plane, foreign ministry spokesman Hong Lei said.
The increasingly large area in question has made it "more and more difficult for us to search for the missing flight. But as long as there is a glimmer of hope, we will try our utmost," Mr. Hong said.
Chinese authorities, who have repeatedly criticized the Malaysian government for its incomplete release of information, have refused to reveal the precise location of their own search, including whether it might include the Tibet and Xinjiang autonomous regions. Those huge territories on China's western flank have been the source of unrest over Beijing's policies, although Beijing has specifically ruled out involvement by ethnic Uighur separatists from Xinjiang, who were blamed for a recent terror attack at a Chinese railway station.
China also offered no insight into whether MH370 could have penetrated Chinese airspace without being noticed by the country's defence systems.
"The Chinese military is earnestly fulfilling their duties of safeguarding China's territorial airspace and land territory," Mr. Hong said.
The Boeing-777 went missing in the early hours of March 8 en route from Kuala Lumpur to Beijing. Information from Malaysian military radar and the jet's own onboard satellite communications equipment has suggested the jet made a sharp change of course around the time its communications halted. Pings from satellite equipment continued for seven more hours, suggesting the aircraft could have continued on for another 4,000 kilometres or more.
Those indications have made it seem likely foul play is involved, although widely-circulated theories posted online offered other possible explanations, including the possibility of an aircraft fire that led the pilots to disable electrical systems to isolate the problem.
Investigators piecing together patchy data from military radar and satellites believe that someone turned off aircraft's identifying transponder and ACARS system, which transmits maintenance data, and turned west, crossing the Malay Peninsula and following a commercial aviation route towards India.
What happened next is less certain. The plane may have flown for another six hours or more after dropping off Malaysian military radar about 200 miles northwest of Penang Island.
But the satellite signals that provide the only clues were not intended to work as locators. The best they can do is place the plane in one of two broad arcs – one stretching from Laos up to the Caspian, the other from west of Indonesia down to the Indian Ocean off Australia – when the last signal was picked up.
Malaysian police have searched the homes of the captain, Zaharie Ahmad Shah, 53, and first officer, Fariq Abdul Hamid, 27, both in middle-class suburbs of Kuala Lumpur close to the international airport.
Among the items taken for examination was a flight simulator Zaharie had built in his home.
A senior police officer with direct knowledge of the investigation said the programs from the pilot's simulator included Indian Ocean runways in the Maldives, Sri Lanka, Diego Garcia and southern India, although he added that U.S. and European runways also featured.
"Generally these flight simulators show hundreds or even thousands of runways," the officer said.
"What we are trying to see is what were the runways that were frequently used. We also need to see what routes the pilot had been assigned to before. This will take time, so people cannot jump the gun just yet."