PERTH, Australia — Four weeks after the Malaysia Airlines jet vanished, two ships deployed sound locators Friday in the southern Indian Ocean in a desperate attempt to find the plane's flight recorders before their signal beacons fall silent.
Officials leading the multinational search for Flight 370 said there was no specific information that led to the underwater devices being used for the first time but that they were brought into the effort because there was nothing to lose.
The air and sea search has not turned up any wreckage from the Boeing 777 that could lead searchers to the plane and perhaps its flight data and cockpit voice recorders, or "black boxes."
The recorders could help investigators determine why the Malaysia Airlines plane, which disappeared March 8 while en route from Kuala Lumpur to Beijing with 239 people aboard, veered so far off-course.
Beacons in the black boxes emit "pings" so they can be more easily found, but the batteries last only about a month.
Two ships with sophisticated equipment that can hear the pings made their way Friday along a 150-mile route that investigators hope might be close to the spot where officials think Flight 370 went down.
"No hard evidence has been found to date, so we have made the decision to search a sub-surface area on which the analysis has predicted MH370 is likely to have flown," Cmdr. Peter Leahy, commander of military forces involved in the search, said in a statement.
The Australian navy ship Ocean Shield towed a pinger locator from the U.S. Navy, while the British navy's HMS Echo was equipped with similar gear.
Because the U.S. Navy's pinger locator can pick up signals to a depth of 20,000 feet, it should be able to hear the plane's data recorders even if they are in the deepest part of the search zone.