Malaysia Airlines Flight 370 Search Zone Narrows: Crews Focus on Picking Up Fading Signals That May Be From 'Black Boxes'

The Wall Street Journal

By Rachel Pannett

April 10, 2014 12:10 a.m. ET

SYDNEY—The search zone for Malaysia Airlines Flight 370 continued to narrow Thursday, as authorities focused on picking up fading signals that may be from the missing jet's "black boxes" before their batteries run out of power.

The Australian authority leading the multinational hunt said more than a dozen planes and 13 ships would patrol an area of about 57,923 square kilometers (22,364 square miles) of the southern Indian Ocean northwest of Perth—the narrowest zone yet in a close to five-week-old search for the jet, which disappeared en route to Beijing from Kuala Lumpur on March 8.

The planes and ships are continuing to scour the surface of the sea for debris that could provide confirmation that Flight 370 went down in the area. Air sorties on Wednesday spotted a large number of objects, but those items fished out of the water by ship crews weren't from the missing plane, according to Australia's Joint Agency Coordination Centre.

Authorities believe they are closing in on the missing jet's likely final resting place after search crews regained contact with underwater pings consistent with emergency locator beacons attached to the flight recorders.

The latest signals, picked up twice on Tuesday, were weaker than the initial pings detected over the weekend, suggesting the recorders' batteries were close to running out of power. Beacons on the plane's two flight recorders have an estimated battery life of about 30 days before they stop emitting signals. It has been more than a month since the plane disappeared.

Investigators believe Flight 370 ran out of fuel and crashed into the ocean after vanishing from civilian radar as responsibility for communicating with the plane was being handed from Malaysian ground control to Vietnam. It was carrying 239 passengers and crew.

On Wednesday, Australia sent a P-3 Orion military aircraft to drop 84 sonar buoys in a remote patch of the southern Indian Ocean, broadly in the same spot where the Australian defense vessel Ocean Shield detected the stream of signals. Each sonar buoy is equipped with a set of underwater microphones that unspool on wires to a depth of 1,000 feet.

The buoys send data through a radio system back to the aircraft for analysis–a technique typically used to track enemy submarines attempting to evade surface radar. Dropped in a pattern across the search area, the buoys could help to triangulate the source or sources of four signals picked up by the Australian navy since April 5.

Ocean Shield has been sweeping a 7-mile strip of water since Friday. It is towing a U.S. Navy device nearly 2 miles beneath the ocean surface, listening for sounds from the black boxes. Other vessels, including the Chinese ship Haixun 01, are also doing an underwater search of an area farther south, though they haven't detected any new signals since late last week.

Unless search crews can pinpoint a more precise location for the signals detected by Ocean Shield—which are up to 15.5 miles apart—undersea vehicles hunting for plane wreckage on the ocean floor would need to cover a zone of about 502 square miles, according to the U.S. Navy, which is coordinating the underwater search. The submersibles travel at walking pace, meaning it could be weeks rather than days before any debris is found.

"The more effort we put into location of where the transmission is coming from, the more certainty we will have that we will find something on the bottom of the ocean," Air Chief Marshal Angus Houston, who is leading the search operation, said Wednesday.

Air Chief Marshal Houston said that search crews still needed hard evidence, such as a photograph of the wreckage, to declare the plane has crashed.

To avoid interfering with the delicate search for signals, authorities are holding back on deploying any other ships or underwater vehicles, though Air Chief Marshal Houston indicated Wednesday such a move wasn't far away. Choosing to deploy the Bluefin-21, a torpedo-shaped submersible drone strapped to the Ocean Shield's deck, would mark another switch in the search, effectively signaling an end to hopes of more signals from the black boxes.

Authorities think the seabed is covered with a thick carpet of silt that might be distorting the signals and could also handicap any undersea vehicles sent to look for plane wreckage using sonar initially and later video cameras. The silt also may hide debris from Flight 370 that likely scattered over a wide area as it sank to the ocean floor, they said.

The two-year underwater hunt for the black boxes of Air France Flight 447, which crashed into the Atlantic Ocean in 2009, provides sobering lessons in the search for Flight 370. The ocean floor in the Air France crash was nearly 2.5 miles deep, with forbidding peaks and valleys. It took small robotic submarines provided by the Woods Hole Oceanographic Institution nearly 60 trips under the surface before the black boxes were discovered.

Source:  http://online.wsj.com