An underwater "black box" locator finally made its debut in the hunt for flight MH370 yesterday, just days before the recorders' signals are due to fall silent.
With batteries that power the boxes due to run out any day and no debris to give search teams an indication of where the plane is, search chief Angus Houston admitted time was running out.
Two ships spent yesterday slowly trawling along a 240-kilometre corridor of the Indian Ocean in the vague hope that the "towed pinger locator", which is dragged along beneath the waves, would pick up the signals.
Watch: How does a 'black box' work?
"The locator beacon will last about a month before it ceases its transmissions, so we're now getting pretty close to the time when it might expire," Houston said.
Malaysia Airlines flight 370 vanished on March 8. Experts say the black boxes will transmit locator signals for a minimum of 30 days, after which time they will fade as batteries run down.
Investigators settled on the small search area after analysing satellite data "pings" picked up after the plane disappeared off radar screens. But Houston admitted that it was a best guess, based on the plane's estimated speed and performance.
"The area of highest probability as to where the aircraft might have entered the water is the area where the underwater search will commence," he said as the Australian navy ship Ocean Shield and the British HMS Echo set off on their mission.
The total search area currently being scoured for debris by 14 planes and nine ships is 217,000 square kilometres.
Malaysia's opposition leader, Anwar Ibrahim, told Britain's Daily Telegraph that he believed Kuala Lumpur had deliberately concealed information about the flight. He said he was "baffled" as to how the aircraft was not picked up by the country's radar system after going off course. "I believe the government knows more than us," he said.
Australian Prime Minister Tony Abbott yesterday met with staff at the Australian Maritime Safety Authority, which is co-ordinating the search effort. He said officials had no idea how long the hunt would continue. "It's probably the most difficult search that's ever been mounted."
Associated Press, Agence France-Presse