By Daniel Stacey
In the rush to locate further signals that may be from Malaysia Airlines Flight 370's "black box" flight recorders, the Australian air force plans to drop sonar buoys typically used in antisubmarine warfare across the current search area.
On Wednesday, Australia sent a P-3 Orion military aircraft to drop the buoys in a remote patch of the southern Indian Ocean some 570 nautical miles off the remote northwest coast of Australia. That is broadly in the same spot where the defense vessel Ocean Shield detected a stream of signals on four separate occasions since Saturday, and where the naval crew is looking for more using a high-tech underwater listening device.
The P-3 Orion is stocked with 84 sonar buoys, each with a sophisticated set of underwater microphones that unspool on wires to a depth of 1,000 feet. The buoys send data through a radio system in its surface unit back to the aircraft for analysis--a technique typically used to track enemy submarines attempting to evade surface radar.
The plane has been configured to listen only for signals around 37.5 kHz sent by the locator beacons, factoring in the potential for lower frequencies as the black boxes run low on batteries and possible distortions for silt slaking the seabed. These signals pulse through the water once per second, said Commodore Peter Leavy, who is commanding the Australian military's involvement in the search.
Dropped in a pattern across the search area, the buoys could help to triangulate the source or sources of four signals the Ocean Shield has picked up since April 5.
The four signals are spaced up to 25 kilometers, or about 16 miles, apart along the "handshake" pathway. This was the estimated flight path for Flight 370, plotted using ping "handshakes" from the aircraft to an Inmarsat PLC telecommunications satellite, and supplemented with estimates of the speed and performance of the Boeing 777-200 provided by its manufacturer and from radar records that captured it in flight.
The spread of these signals means that experts have defined a 1,300 square-kilometer, or around 500 square-mile, search zone, to be covered by undersea submersible vehicles when a decision is made to deploy them, said Capt. Mark Matthews of the U.S. Navy, who is coordinating the underwater search from Perth.
Capt. Matthews estimated that the Bluefin-21 underwater drone aboard the Ocean Shield can only scan around 30 square kilometers a day. That means this new effort to narrow the area using sonar buoys is critical to quicken the search. Otherwise, crews may need to spend up to a month and half mapping the area with side-scan sonar technology to find the missing plane.
Write to Daniel Stacey at daniel.stacey@wsj.com
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