Researchers at Perth's Curtin University are examining a low-frequency underwater sound signal that could have resulted from Malaysian Airlines Flight MH370 crashing into the Indian Ocean.
Dr Alec Duncan, from Curtin University's Centre for Marine Science and Technology team, believes there is slim chance - perhaps as low as 10 per cent - the low frequency signal could have been MH370 either hitting the water or a part of the aircraft imploding as it sank to the bottom of the ocean.
However he conceded the signal, picked up by underwater sound recorders off Rottnest Island just after 1.30am (UTC) on March 8 - consistent with the disappearance of MH370 - more likely originated from a natural event, such as a small earth tremor.
A scaled back search for MH370 continues off the WA coast after the Australian Transport Safety Bureau declared that in its professional judgement, the search zone could be discounted as the final resting place of the missing aircraft.
The signal detected by the Curtin University team has since been correlated with another underwater listening station, run by the United Nations' Comprehensive Nuclear-Test Ban Treaty Organisations,140 kilometres off Cape Leeuwin.
“Soon after the aircraft disappeared, scientists at CTBTO analysed data from their underwater listening stations south-west of Cape Leeuwin and in the northern Indian Ocean. They did not turn up anything of interest,” Dr Duncan said.
“But when the MH370 search area was moved to the southern Indian Ocean, scientists from Curtin’s Centre for Marine Science and Technology decided to recover the IMOS acoustic recorders located west of Rottnest Island."
Although only one of the two acoustic recorders was recovered, Dr Duncan said analysis of the recordings picked up a significant low-frequency noise.
“Data from one of the [Rottnest] recorders showed a clear acoustic signal at a time that was reasonably consistent with other information relating to the disappearance of MH370," Dr Duncan said.
“The crash of a large aircraft in the ocean would be a high energy event and expected to generate intense underwater sounds.”
"We sent the data to search authorities and I got a phone call at 3am in the morning so they were definitely interested in it."
Dr Duncan said the timing of the signal (consistent with the disappearance of the aircraft), the fact that it was a long-distance event and the north-west direction of the frequency were the three factors that gave researchers hope the noise may have been caused by MH370.
“It has since been matched with a signal picked up by CTBTO’s station south-west of Cape Leeuwin," Dr Duncan said.
“A very careful re-check of data from that station showed a signal, almost buried in the background noise but consistent with what was recorded on the IMOS recorder off Rottnest.
“The CTBTO station receives a lot of sound from the Southern Ocean and Antarctic coastline, which is why the signal showed up more noticeably on the Rottnest recorder.
“Using the three hydrophones from the Cape Leeuwin station, it was possible to get a precise bearing that showed the signal came from the north-west.
But Dr Duncan conceded there were large uncertainties in the estimate and that it was "not compatible" with satellite "handshake" data transmitted from the aircraft, currently considered the most reliable source of information.
"We don't know if it is related to the aircraft, we only have circumstantial evidence of that, whereas the information they have from the satellite handshake data they do know is from the aircraft, so that's a very big difference," he said.
However Dr Duncan said the data had attracted significant interest from search authorities, and would likely be used to focus the search area.
He described the discovery as "tantalising".
"They've been encouraging us considerably to keep on looking at it and to refine the numbers. I've been over to Canberra to talk to them and we continue to have a very close relationship with them," Dr Duncan said.
"They've provided us with some financial support as well for us to be able to continue working on it and they feel the same way that we do about it.
"It's sort of tantalising, it's sort of something that 'whoah, it could be something really useful but' there's these other factors that say maybe it's not."
"I think, you know, a low percentage [that the noise originated from MH370], maybe 10 per cent or something like that but it's really hard to put numbers on something like that.
"In underwater acoustics you never really know what you're listening. This is another example of that.
"We haven't given up on it. In the fullness of time we will be recovering other loggers that we have scattered around the country that we think have only a very low chance of having recieved the same event. But we will have a look at that data.
"This is such an incredible mystery, and we find ourselves in a unique position to be able to contribute to hopefully solving it.
"There's a large number of families who have no idea what happened to their loved ones. If we can do anything that will help them then that's something that will be really worthwhile."
MH370 departed Malaysia's Kuala Lumpur International Airport on March 8 bound for Beijing, carrying 12 Malaysian crew members and 227 passengers from 14 nations, including seven Australians.
It would never arrive at its destination, with Malaysian air traffic control losing contact with the aircraft less than an hour after takeoff.
While the initial search area focused on the South China Sea and the Gulf of Thailand, it quickly shifted to the coast of Western Australia, with authorities focusing on a 319,000 square kilometre area of the Indian Ocean 2,600 kilometres south-west of Perth.
But the search is now effectively on hiatus, with no aircraft and just one ship, a Chinese survey vessel, actively searching for MH370 after ATSBU discounted the search area, when acoustic pings, thought to be from flight data or the cockpit voice recorder of MH370, were determined to have come from another, man-made source.
However, the federal government has still pledged $89.9 million over two years towards the search in the 2014 Federal Budget.