Australian Defense Force/Handout via Reuters

New ‘possible signal’ detected in Malaysian plane search

Search zone for missing Malaysia Airlines Flight 370 is now narrowed to its smallest size yet

An Australian aircraft hunting for the missing Malaysia Airlines Flight 370 detected a possible new underwater signal on Thursday, in the same area where search crews previously detected pulses that were consistent with those from a plane’s “black box” flight recorders.

The search zone has now been narrowed down to its smallest size yet in the monthlong hunt for the plane, a day after the Australian official in charge of the search expressed hope that crews were closing in on the "final resting place" of the vanished jet.

An Australian navy P-3 Orion search plane, which has been dropping signal-locating buoys into the water near where the original pulses were detected, on Thursday picked up a "possible signal" that may be from a man-made source, said Angus Houston, who is coordinating the search off Australia's west coast.

"The acoustic data will require further analysis overnight," Houston said in a news release.

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 signals, and an analysis of two other pulses detected in the same general area on Saturday showed they were consistent with a plane's black boxes. The planes and ships hunting for the missing jet subsequently zeroed in on a targeted patch of the Indian Ocean.

"We are still a long way to go, but things are more positive than they were some time ago," Martin Dolan, chief commissioner of the Australian Transport Safety Board, which is involved in the search mission, told Reuters on Thursday.

"I'm now optimistic that we will find the aircraft, or what is left of the aircraft, in the not-too-distant future," Houston said Wednesday.

Frustrating search

Meanwhile, 14 planes and 13 ships were looking for floating debris across the 22,300-square-mile search zone, about 1,400 miles northwest of Perth, and China's patrol ship Haixun 01 was using underwater acoustic equipment to search for signals in an area several hundred miles south of the Ocean Shield. A "large number of objects" had been spotted by crews combing the area on Wednesday, but the few that had been retrieved by search vessels were not believed to be related to the missing plane, the coordination center said.

Search crews hunting for debris had already looked in the area they were crisscrossing on Thursday, but are moving in tighter patterns now that the search zone has been narrowed to about a quarter the size it was a few days ago, Houston said.

Finding the flight data and cockpit voice recorders soon is important because their locator beacons have a battery life of about a month, and Tuesday marked one month since Flight 370 vanished.

If the batteries fail before the recorders are located, finding them in such deep water — about 15,000 feet — would be difficult, if not impossible.

The hope expressed by Houston on Wednesday contrasted with the frustrating monthlong search for the Boeing 777, which disappeared shortly after takeoff in one of the biggest mysteries in aviation history. The plane veered off course for an unknown reason, with officials saying satellite data indicate it went down in the southern Indian Ocean. The black boxes could help solve that mystery.

The signals detected 1,020 miles northwest of Perth by the Ocean Shield are the strongest indication yet that the plane crashed and is at the bottom of the ocean in the area where the search is now focused.

A data analysis of the signals heard Saturday determined they were distinct and man-made and that they pulsed consistently, Houston said.

To assist the Ocean Shield, the Australian navy dropped 84 sonobuoys by parachute in a pattern near where the signals were last heard.

Royal Australian Navy Commodore Peter Leavy said each buoy will dangle a hydrophone listening device about 1,000 feet below the surface. The hope, he said, is that the buoys will help better pinpoint the signals.

But experts say the process of teasing out the signals from the cacophony of background noise in the sea is a slow and exhausting process. Operators must separate a ping lasting just 9.3 milliseconds — a tenth of the blink of a human eye — and repeated every 1.08 seconds from natural ocean sounds, as well as disturbances from search vessels.

Houston acknowledged that searchers were running out of time, noting that the last two signals were weaker and briefer than the first pair heard Saturday, suggesting the batteries are failing.

The weakening of the signals also could indicate the device was farther away, U.S. Navy Capt. Mark Matthews said. Temperature, water pressure or the saltiness of the sea could also be factors. Thick silt on the ocean floor could also distort the sounds and may hide wreckage from the eventual visual search, he said.

The coordination center said Thursday that searchers had not yet deployed an unmanned submarine to create a sonar map of a potential debris field on the seabed.

Matthews said the detections indicate the beacon is within about a 12-mile radius, equal to a 500-square-mile chunk of the ocean floor — an area the size of Los Angeles.

The Bluefin 21 sub takes six times longer to cover the same area than the ping locator, and it would take the vehicle about six weeks to two months to canvass the current search zone. That's why the ping locator is still being used to home in on a more precise location, Matthews said. The underwater search zone falls within the larger area that is being scoured for floating debris.

The underwater search was narrowed to its current position after engineers predicted a flight path by analyzing signals between the plane and a satellite and investigators used radar data to determine the plane's speed and where it may have run out of fuel.

Houston noted that all four of the pings detected since Saturday were near the site of a final, partial "handshake" signal revealed earlier in the investigation.

Al Jazeera and wire services

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