The planned search area for Saturday.

The planned search area for Saturday. Photo: AMSA

Australia has dispatched six planes, including a pair of commercial jets with volunteer observers, to patrol the southern Indian Ocean for the missing Malaysian airliner that disappeared two weeks ago.

The chartered aircraft bolster the hunt in the region 2,500 kilometres southwest of Perth. Australia said two merchant vessels were in the area, while the Xinhua News Agency said China, whose nationals made up most of Flight 370's passengers, is deploying at least seven ships.

Saturday's missions follow a shift to emphasize a visual search yesterday after radar scans failed to locate two objects whose sightings via satellite kindled hopes of a breakthrough in the mystery of Malaysian Air Flight 370. Investigators are focused on a 36,000 km sq zone in what has become the longest disappearance ever for a modern passenger jet.

"It's about the most inaccessible spot you could imagine on the face of the Earth," Prime Minister Tony Abbott said yesterday.

The Australian Maritime Safety Authority said 10 State Emergency Service volunteers from Western Australia were flying today aboard what it described as "ultra-long-range commercial jets." The aircraft were chartered, according to the agency, which didn't elaborate on the owners or any other arrangements.

The ultra-long-range jets have the capability of five hours of search time, compared with two hours for the other jets because of the distance from the search area, it said.

Friday's air search involved five planes. HMAS Success from the Royal Australian Navy is heading to the search area and is due there later Saturday, AMSA said in its daily update.

Chinese Flotilla

China's flotilla reflects the urgency the country attaches to finding Flight 370, whose complement of 239 passengers and crew included more than 150 Chinese. The U.S., which also is searching the southern Indian Ocean, was asked by Malaysia to provide underwater search technology, the Defense Department said in a statement.

The Australian satellite images that galvanised the latest push in the search were taken on March 16 and showed two objects: one piece as big as 24 metres, and a second one as big as 5 metres. Poor weather hampered Friday's patrols.

'Big Area'

"Although this search area is much smaller than what we started with, it nonetheless is a big area when you're looking out the window and trying to see something by eye," John Young, general manager of emergency response at the Australian Maritime Safety Authority, said on Friday. "We may have to do this a few times to be confident about the coverage of this search area."

An analysis of satellite pings shows that Malaysian Airline System Bhd. Flight 370 may have cruised steadily across the ocean after diverting from its scheduled route to Beijing from Kuala Lumpur. That assessment gave the clearest idea yet on how investigators pinpointed a search zone.

London's Daily Telegraph published the transcript of the communication between the cockpit and ground control, which included instructions on takeoff and flight altitude. The exchange ended with the cockpit's response of "All right, good night" at 1.19am, similar to initial investigation that showed the co-pilot's last words as the plane left Malaysian airspace.

Seven Positions

Engineers at Inmarsat Plc, whose satellite picked up the pings, plotted seven positions for the Boeing Co. 777-200ER on March 8, Chris McLaughlin, a company spokesman, said in an interview. The plane flew steadily away from the satellite over the equator while pinging, McLaughlin said. Malaysia needs to verify that information, Azharuddin Abdul Rahman, the chief of the nation's civil aviation, said in Kuala Lumpur.

The data helped investigators conclude that the most logical path was progressively either north or south. U.S. investigators have focused the search to the south, where Australia is leading the ocean-search efforts.

When officials estimated the plane was flying at or near its cruising speed of more than 800 kilometres per hour, it produced a probable path the engineers were "very confident" about, McLaughlin said.

Arc Estimate

The engineers don't know the plane's track for certain because the satellite pings can only be used to estimate an arc along the Earth's surface where it would have been, he said.

"You can assume the tracking was based on what the autopilot was set for on the 777," he said.

If the Inmarsat estimates are accurate, it would have been impossible for the plane to have landed before its satellite transmitter sent the final ping at 8:11 a.m., almost seven hours after its last known position as it left Malaysian airspace, according to McLaughlin's account. Because the 777 burns more fuel at lower altitude, it also suggests the plane remained at cruising altitude.

The plane was flying at 872 kph at 10,668 meters at 1:21 a.m. when its transponder stopped functioning and it disappeared from Malaysian's civilian radar system, according to FlightRadar24, a flight-tracking company.

The engineers at Inmarsat were able to validate their estimates of the plane's location by matching its position at 1:07 a.m., when it sent a burst of data through its Aircraft Communications and Reporting System, McLaughlin said. That final transmission on Acars included a GPS position that was used to calibrate the other estimates, he said.

The Inmarsat analysis is consistent with details suggesting that, at least initially, the path was commanded from the cockpit, John Cox, president of Washington-based Safety Operating Systems, said in an interview. It still doesn't answer what may have happened to the plane and what led it to fly for so long, he said.

--With assistance from Jason Scott in Canberra, Michael Sin and Michael Heath in Sydney, Barry Porter and Manirajan Ramasamy in Kuala Lumpur, Shamim Adam in Singapore and Gopal Ratnam and John Hughes in Washington.