MH-370 signals (1300 sq km wide, 6.5 km deep)

The hunt for the black box recorder goes on, now concentrated on a Los Angeles size area in the Indian Ocean.

It is one level of miracle to pin-point the pings (which are due to be switched off any time now, there is a grace period of about 10 days) and quite another (impossible) challenge to retrieve the recorder from extreme depths (worst case scenario: it is in a trench 5800m deep).
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An Australian aircraft picked up a new underwater signal on Thursday while searching the same part of the Indian Ocean where earlier sounds were detected that were consistent with an aircraft's black boxes.

If confirmed, this would be the fifth underwater signal detected in the hunt for Flight 370, which vanished on March 8 while flying from Kuala Lumpur, Malaysia, to Beijing, with 239 people aboard.


On Tuesday, the Australian vessel Ocean Shield picked up two underwater sounds, and an analysis of two other sounds detected in the same general area on Saturday showed they were consistent with a plane's flight recorders, or "black boxes."
 

The Australian navy has been dropping buoys from a P-3 Orion to better pinpoint the location of the sounds detected by the Ocean Shield.
 

Royal Australian navy commodore Peter Leavy said each buoy is dangling a hydrophone listening device about 300 meters (1,000 feet) below the surface. Each buoy transmits its data via radio back to the plane.
 

The underwater search zone is currently a 1,300 square kilometre (500 square mile) patch of the ocean floor, and narrowing the area as small as possible is crucial before an unmanned submarine can be sent to create a sonar map of a potential debris field on the seabed.
 

The Bluefin 21 sub takes six times longer to cover the same area as the pinger locator being towed by the Ocean Shield, and it would take the vehicle about six weeks to two months to canvass the underwater search zone, which is about the size of Los Angeles. That's why the acoustic equipment is still being used to hone in on a more precise location, US navy Capt. Mark Matthews said.
 

The search for floating debris on the ocean surface was narrowed on Thursday to its smallest size yet — 57,900 square kilometers (22,300 square miles), or about one-quarter the size it was a few days ago. Fourteen planes and 13 ships were looking for floating debris, about 2,300 kilometers (1,400 miles) northwest of Perth.
 

A "large number of objects" were spotted on Wednesday, but the few that had been retrieved by search vessels were not believed to be related to the missing plane, the search coordination centre said.

The locator beacons on the black boxes holding the flight data and cockpit voice recorders have a battery life of about a month, and Tuesday marked one month since Flight 370 disappeared. The plane veered off-course for an unknown reason, so the data on the black boxes are essential to finding the plane and solving the mystery. Investigators suspect it went down in the southern Indian Ocean based on a flight path calculated from its contacts with a communications satellite and analysis of its speed and when it would have run out of fuel.
 

An Australian government briefing document circulated among international agencies involved in the search on Thursday said it was likely that the acoustic pingers would continue to transmit at decreasing strength for up to 10 more days, depending on conditions.
 

Once there is no hope left of the Ocean Shield's equipment picking up any more sounds, the Bluefin sub will be deployed. Complicating matters, however, is the depth of the seafloor in the search area. The pings detected earlier are emanating from 4,500 meters below the surface — which is the deepest the Bluefin can dive.

Williams said colleagues at the Woods Hole Oceanographic Institution in Massachusetts had autonomous and remotely operated underwater vehicles that will dive to 11 kilometers (36,100 feet), although they might not be equipped for such a search.
 

Underwater vessels rated to 6,500 meters (21,300 feet) could search the sea bed of more than 90 percent of the world's oceans, Williams said. "There's not that much of it deeper than six and a half kilometers," he said.
 

Williams said it was unlikely that the wreck had fallen into the narrow Diamantina trench, which is about 5,800 meters (19,000 feet) deep, since sounds emanating from that depth would probably not have been detected by the pinger locator.

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regards