Jet search 'will go on a long time'
Australia's prime minister has said the massive search for the missing Malaysian jet is likely to continue "for a long time" as electronic transmissions from the dying black boxes are fading fast.
Tony Abbott appeared to soften his comments from yesterday while on a visit to China, where he met president Xi Jinping.
He had said he was "very confident" that signals heard by an Australian ship towing a US Navy device that detects flight recorder pings were coming from the Boeing 777.
He has continued to express this belief but, with no new underwater signals detected, he added that the job of finding the plane that disappeared on March 8 remains arduous.
"No one should underestimate the difficulties of the task still ahead of us," he said on the last day of his China trip.
"We have very considerably narrowed down the search area, but trying to locate anything 4.5 kilometers beneath the surface of the ocean about 1,000 kilometers from land is a massive, massive task and it is likely to continue for a long time to come."
After analysing satellite data, officials believe the plane with 239 people aboard flew off course for an unknown reason and went down in the southern Indian Ocean off the west coast of Australia.
Search crews are scrambling because the batteries powering the recorders' locator beacons last only about a month, and that window has already passed. Finding the devices after the batteries die would be extremely difficult due to the depth of the water.
Two sounds heard a week ago by the Australian ship Ocean Shield, towing the ping locator, were determined to be consistent with the signals emitted from the black boxes. Two more pings were detected in the same general area on Tuesday.
Mr Abbott said: "Given that the signal from the black box is rapidly fading, what we are now doing is trying to get as many detections as we can, so that we can narrow the search area down to as small an area as possible."
The underwater search zone is a 500-square mile patch of the seabed.
The searchers want to pinpoint the exact location of the source of the sounds - or as close as they can get - and then send down a robotic submersible to look for wreckage, but the sub will not be deployed until officials are confident there are no other electronic signals.
The Bluefin 21 submersible takes six times longer to cover the area as the ping locator. That is about six weeks to two months to canvass the current underwater zone.
The signals are coming from 15,000ft below the surface, which is the deepest the Bluefin can dive. The search co-ordination centre said it was considering options in case a deeper-diving sub is needed.
The surface area to be searched for floating debris has been narrowed to 16,000 square miles of ocean extending from about 1,400 miles north west of Perth. Up to 10 planes and 14 ships are searching.