Following four strong underwater signals in the past week, all has gone quiet in the search for the missing Malaysia Airlines jet, meaning the batteries in the plane's all-important black boxes may finally have died.
Despite having no new transmissions from the black boxes' locator beacons to go on, air and sea crews were continuing their search in the southern Indian Ocean for debris and any sounds that may still emanate. They were desperately trying to pinpoint where the Boeing 777 could be amid an enormous patch of deep ocean.
No new electronic pings had been detected since Tuesday by an Australian ship dragging a US Navy device that listened for flight recorder signals. Once officials were confident that no more sounds would be heard, a robotic submersible would be sent down to slowly scour for wreckage.
''We're now into Day 37 of this tragedy,'' said aviation expert Geoffrey Thomas.
''The battery life on the beacons is supposed to last 30 days. We're hoping it might last 40 days. However, it's been four or five days since the last strong pings. What they're hoping for is to get one more, maybe two more pings so they can do a triangulation of the sounds and try and narrow the (search) area.''
Recovering the plane's flight data and cockpit voice recorders was essential for investigators to try to figure out what happened to Flight 370, which vanished March 8. It was carrying 239 people, mostly Chinese, while en route from Kuala Lumpur, Malaysia, to Beijing.
After analysing satellite data, officials believed the plane flew off course for an unknown reason and went down in the southern Indian Ocean off Australia's west coast.
Investigators trying to determine what happened to the plane were focusing on four areas - hijacking, sabotage and personal or psychological problems of those on board.
Two sounds heard a week ago by the Australian ship Ocean Shield, which was towing the ping locator, were determined to be consistent with the signals emitted from black boxes. Two more pings were detected in the same general area Tuesday, but no new ones have been picked up since then.
Australian Prime Minister Tony Abbott has expressed confidence that the pings picked up by the Ocean Shield were coming from the plane's two black boxes, but he cautioned that finding the actual aircraft could take a long time.
''There's still a lot more work to be done and I don't want anyone to think that we are certain of success, or that success, should it come, is going to happen in the next week or even month. There's a lot of difficulty and a lot of uncertainty left in this,'' Abbott said Saturday in Beijing, where he was wrapping up a visit to China.
Searchers want to pinpoint the exact location of the source of the sounds - or as close as they can get - before sending the Bluefin 21 submersible down. It would not be deployed until officials were confident that no other electronic signals would come, and that they have narrowed the search area as much as possible.
The underwater search zone was currently a 1300-square-kilometre patch of the seabed, about the size of Los Angeles.
The sub would take six times longer to cover the same area as the ping locator, and would need about six weeks to two months to canvas the current underwater zone. The signals were also coming from 4500 metres below the surface, which was the deepest the sub can dive.
The surface area being searched on Sunday for floating debris was 57,506 square kilometres of ocean extending about 2200km northwest of Perth. Up to 12 planes and 14 ships were participating in the search.