Perth: The final resting place of missing Malaysia Airlines plane MH370 has been narrowed says Australia.
More signals have been detected revealed search chief Angus Houston at a news conference in Perth.
"Ocean Shield has been able to reacquire the signals on two more occasions, late yesterday afternoon and later last night," said Houston, head of the Joint Agency Coordination Centre.
"Ocean Shield has now detected four transmissions," he said as searchers try to poinpoint wreckage from the Boeing 777 that disappeared on March 8 with 239 people on board.
He said the most recent 'ping' was received late last night (Perth time) which lasted seven minutes and another, lasting 5 minutes 32 seconds was detected earlier in the afternoon.
In all there have been four reports of acoustic signals in the same area, on Saturday 5 April at 4.45 pm (Perth time) and again at 9.27 pm. The next set was on Tuesday 8 April at 4.27 pm and later at 10.17 pm.
Houston said data analysis of the first two acoustic signals established that the pulse was not of natural origin, and more likely from a flight data recorder.
"The analysis determines that a very stable distinct and clear signal was detected at 33.331 kHz and that it consistently pulsed at a 1.106 second interval.
"They therefore assessed that the transmission was not of natural origin and was likely sourced from specific electronic equipment.
"They believe the signals to be consistent with the specification and description of a flight data recorder," he said.
The retired air marshal added he was confident the hunt was now in the right area but a sighting of wreckage was needed to be certain.
"Hopefully with lots of transmissions we'll have a tight, small area and hopefully in a matter of days we'll be able to find something on the bottom that might confirm that this is the last resting place of MH370," Houston told reporters.
He added "we are now searching a more concentrated area" adding that the smaller area allows for a tighter search pattern and visual search for debris.
Responding to the media, the Joint Agency Coordination Centre (JACC) head said "This is a great lead. I'm optimistic we will find the aircraft, or what's left of the aircraft".
He added that once the underwater vehicle is deployed, the hope is that "within days we can get a visual sighting of the wreckage".
But he remained cautious, warning that there is much silt at the bottom of the ocean floor which affect sound and visual searches, and that the batteries of the black box could be weakening.
Authorities have been searching a linear arc produced from satellite data believed to represent the last stretch of the plane's flight path, hoping to pick up the pings from the black box recorders.
Houston said the first "pings", picked up on Saturday afternoon and evening, were near the final radar "handshake" the plane made with satellites.
Up to 11 military aircraft, four civil aircraft and 14 ships were searching Wednesday over a zone covering 75,423 square kilometres (29,000 square miles), JACC said.
The focus of the search area is 2,260 kilometres (1,400 miles) northwest of Perth and JACC said scattered showers were forecast for Wednesday.
Officials say a submersible US-made sonar device called a Bluefin 21 will not be launched to comb the seabed until it was clear batteries that may be emitting pings from the black boxes had expired.
Houston said officials were probably close to using this device because the last acoustic signal was very weak, indicating the batteries were running down.
"I don't think that time is very far away," he said.
The case of the missing jet has baffled aviation experts and frustrated the families of those on board, two-thirds of whom were Chinese.
Despite extensive searches on the ocean surface, no debris from the flight has yet been found.
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