PERTH - Planes and ships in the search for a missing Malaysian airliner were deployed Monday to verify whether underwater signals are from the jet's black box, as the clock ticks on its battery life.
Three separate signals have been detected by Australian and Chinese vessels, raising hopes of solving the mystery of Flight MH370 which disappeared on March 8 and is believed to have crashed in the southern Indian Ocean.
Angus Houston, the former Australian defence chief who is leading the search coordination body, has said that two pulses detected by Chinese vessel Haixun 01 are an "important and encouraging lead".
But experts have voice scepticism over the signals, which the Haixun 01 said were on a frequency used for the plane's flight data and cockpit voice recorders, and urged caution until better-equipped ships and air force planes reach the area.
"Haixun remains in the position, attempting to regain the pinger signal," Houston's Joint Agency Coordination Centre (JACC) said Monday.
It said that the British naval vessel HMS Echo "has now joined her to assist in the search".
A third acoustic signal, picked up by the Australian vessel Ocean Shield, was also being scrutinised, 300 nautical miles away from the Chinese ship in the remote search zone far off the west coast of Australia.
Australia's JACC said that in total up to nine military planes, three civil planes and 14 ships were to take part in Monday's search operation.
Houston said Sunday the signal detections were being taken "very seriously" as the lifespan deadline loomed on the black box tracking beacons, which typically transmit for one month but can continue for another eight to 10 days.
Australian authorities have said the Haixun 01 had twice picked up a signal -- once for 90 seconds on Saturday and another more fleeting "ping" on Friday a short distance away.
"This is an important and encouraging lead but one which I urge you to continue to treat carefully," Houston told reporters.
"We are working in a very big ocean and within a very large search area."
He said Haixun 01 was in waters about 4.5 kilometres (nearly three miles) deep, meaning "any recovery operation is going to be incredibly challenging and very demanding and will take a long period of time" if the plane is found there.
The search area was expected to be approximately 234,000 square kilometres on Monday, JACC said, predicting good weather throughout the day in a region which is regularly hit with storms and mountainous seas.
- Time running out -
The Malaysia Airlines flight was on a flight from Kuala Lumpur to Beijing with 239 people aboard when it vanished, veering wildly off course for reasons that remain unknown.
A criminal probe has centred on hijacking, sabotage or psychological problems among passengers or crew, but there is no evidence yet to support any of the theories.
No debris has yet been found despite extensive aerial and sea searches, prompting authorities to focus more on undersea acoustic surveillance in hopes of finding the aircraft.
The hunt was adjusted to the southern end of the search zone Sunday after corrected satellite data showed it was more likely the plane entered the water there.
Houston said the Haixun 01 was already operating in that more southerly zone.
Some analysts greeted the acoustic detections with optimism, saying a 37.5kHz signal can only be transmitted by an emergency beacon. But others were sceptical and said it was vital to find supporting evidence.
- Hope, scepticism over signal -
Australian aviation analyst Geoffrey Thomas said the Chinese signals were detected using a simple handheld device called a hydrophone which was lowered into the water on a probe from the side of a dinghy.
The device is designed for "shallow detection work" by divers and Thomas questioned whether it was capable of picking up a signal from 4.5 kilometres below the surface, saying it was the "the most low-tech solution you can think of".
"It certainly could pick up this signal, but it's picking it up at the extreme end of the range of detection," he told AFP, saying that while it was an improbable outcome, so was the disappearance of the plane.
"The Chinese could have stumbled on it, you can't discount it at all and I think the fact that Australia is sending ships to the area means they are not discounting it."
Greg Waldron, Asia managing editor of Flightglobal magazine, was also sceptical that the Chinese ship had picked up a pulse from the black box.
"There have been a lot of false leads in this story and we need to be extremely cautious with any information that comes," he told AFP.
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