Sydney - Eleven planes and 14 ships were scouting the Indian Ocean on Sunday for traces of a Malaysia Airlines plane that disappeared five weeks ago on a flight from Kuala Lumpur to Beijing with 239 people on board.
No new acoustic signals that could be from the Boeing 777's flight recorders have been detected since Tuesday, raising fears that their batteries have given out.
The search ship Ocean Shield first heard a promising acoustic signal on April 5, and then again three days later, but since then there have been no new transmissions monitored by the special device the vessel is towing.
The Joint Agency Coordination Centre in the west-coast Australian city of Perth said fresh signals were needed to justify sending down an underwater probe, to scan the ocean floor for debris from flight MH370 that could include the flight data recorder and the cockpit voice recorder.
The centre said in its latest bulletin that the "work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed.
"The batteries in the plane's flight recorders have passed their regulation one-month life span.