Malaysia Airlines MH370: Ocean Shield detects signal 'consistent' with black box recorder

Updated

The pinger locator deployed by Australia's Ocean Shield defence vessel in the search for missing Malaysia Airlines flight MH370 has detected signals consistent with those emitted by a black box flight recorder.

Retired Air Chief Marshal Angus Houston, who is leading the international search effort, says it is the "most promising lead" so far in the hunt for the plane, which went missing on March 8 with 239 people on board.

However, he has urged caution, saying it could take several days before the signals can be definitely linked to the missing flight.

Air Chief Marshal Houston says a long, consistent underwater signal was picked up for two hours and 20 minutes within "the northern part of the defined search area".

"What we've got is a visual representation on the screen, and we've also got an audible signal [that] sounds to me just like an emergency locator beacon," he said.

The signal was lost before being detected for a second time by the Ocean Shield for 13 minutes.

"On this occasion two distinct pinger returns were audible. Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," Air Chief Marshal Houston said.

The signals are in addition to the "acoustic noise" Ocean Shield picked up a few days ago, and the two electronic pulse signals identified by the Chinese ship Haixun 01 at the weekend, about 600 kilometres away.

Sorry, this video has expired Video: Watch Air Chief Marshal Angus Houston discuss the signals detected by the Ocean Shield (ABC News)

It is unclear if the two ships have detected the same signal, but Malaysia's acting transport minister Hishammuddin Hussein says he is cautiously optimistic.

"The new development over the last few hours has been the most promising lead we have had," he told a press conference on Monday night.

"I urge all Malaysians and the international community to unite in their prayers, and not give up hope. We will continue with all our efforts to find MH370."

Ocean Shield is staying in the area until it can verify or discount the detections as being from MH370 - a task which could take days.

Air Chief Marshal Houston says once the position of the signal is pinpointed, the Ocean Shield will lower autonomous underwater vessel Bluefin-21, which will search for wreckage on the sea floor.

The Bluefin-21 works primarily as a sonar device. If it detects something unusual on the ocean floor, it will be brought back to the surface and re-equipped with a video recorder, and then sent back to film the area.

It has now been more than one month since the plane went missing, and that means it is one day past the advertised shelf life of the distress locator beacon on the black boxes.

How can multiple pings be detected in different locations at similar times?

So from now on, the sonar-detecting role of the Bluefin-21 will become more and more important.

What is perplexing for many lay observers in the increasingly sonar and sound-focused search is the confusing notion that multiple pings could be detected in different locations at seemingly similar times.

Commodore Peter Levy is in charge of the military taskforce, and today he explained it this way.

"Unlike in air, where sound travels in a straight line, acoustic energy, sound, through the water is greatly affected by temperature, pressure, and salinity. That has the effect of attenuating, bending, sometimes through 90 degrees, soundwaves," he said.

"So it is quite possible, and very hard to predict, it's quite possible for sound to travel great distances laterally but be very difficult to hear near the surface of the ocean for instance.

"So it is a markedly different environment to what you see with sound travelling through air."

Despite sightings of debris from the air, no wreckage has been recovered from the ocean surface by search vessels.

On Monday nine military and three civilian aircraft along with 14 ships were involved in the hunt.

But what may count the most is the ability of the Ocean Shield's crew to reacquire the acoustic signal, and help narrow down the area of ocean floor where the black boxes are probably located.

"If they gain another acoustic event on that towed pinger locator, that will be the trigger at the moment to launch the autonomous underwater vehicle with a more accurate sonar and, potentially, camera for mapping and visually looking at the ocean floor," Commodore Levy said.

If all goes to plan, the search zone for the black boxes could be reduced to a three square mile box.

Topics: disasters-and-accidents, air-and-space, wa, australia, malaysia

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