A MYSTERY underwater sound detected by a pressure monitor could be the last known trace of a doomed jet that vanished over a decade ago, researchers believe.
Malaysia Airlines' MH370 flight, with 239 people onboard, disappeared from radars as it flew into Vietnamese air space en route to Beijing.
On March 24, 2014, 16 days after the plane went missing, the Malaysian Government concluded that "Flight MH370 ended in the Southern Indian Ocean".
Its disappearance sparked the biggest search in aviation history with the whereabouts of the jet still unknown to this day.
Now, researchers at Cardiff University have provided fresh hope for a new search after analysing over 100 hours of underwater audio from historical aircraft accidents and a submarine disappearance.
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Experts believe that this analysis could finally solve the mystery of MH370.
They have already pinpointed an underwater signal in the ocean that could have been caused by the impact of the jet hitting the waves.
The official MH370 narrative suggests the plane made a bizarre U-turn, flying across Malaysia, turning northwest at Penang Island and across the Andaman Sea.
Data from military radar Inmarsat satellite communications network revealed that the plane then flew until at least 8.19am, travelling south into the Southern Indian Ocean.
Many theories have since emerged about what happened to those onboard MH370 and where the jet's final resting place could be.
Mathematician and engineer Dr Usama Kadri says a network of hydrophones used to monitor pressure changes in the ocean as part of a nuclear explosion detection system could be the answer.
Usama and his team trawled through 100 hours of data before looking at signals from the time that MH370 vanished over the Southern Indian Ocean.
There appeared to be one unidentified event in an area known as the Seventh Arc that was picked up at the Leeuiwn station.
The Seventh Arc is an area of the ocean where the last known satellite communication with MH370 occurred.
Hydrophones were being used at Western Australia's Cape Leeuwin and the United States Indian Ocean naval base at Diego Gracia on the night of March 8, according to Dr Kadri.
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He thinks they could have detected the sounds made by MH370 as it crashed.
Writing in The Conversation he said: "A 200-tonne aircraft crashing at a speed of 200 metres per second would release the kinetic energy equivalent to a small earthquake.
"It would be large enough to be recorded by hydrophones thousands of kilometres away.
"Given the sensitivity of the hydrophones, it’s highly unlikely that a large aircraft impacting the ocean surface wouldn’t leave a detectable pressure signature, particularly on nearby hydrophones.
"But unfavourable ocean conditions could potentially dampen or obscure such a signal."
When an airplane crashes into the ocean it creates unique acoustic signatures which can travel more than 3,000km through water.
Audio from these violent impacts could be recorded by a network of 11 hydroacoustic stations worldwide that are dotted along the seabed.
However, the signal picked up near the Seventh Arc at the Leeuiwn station didn't exactly fit with the crash timeline from the official search.
Dr Kadri said the search would have to be revisited to determine whether other signals from the time might be related to MH370.
Usama added: "Given the sensitivity of the hydrophones, it’s highly unlikely that a large aircraft impacting the ocean surface wouldn’t leave a detectable pressure signature, particularly on nearby hydrophones.
"But unfavourable ocean conditions could potentially dampen or obscure such a signal.
"The analysis identified only one relevant signal in the direction of the seventh arc, recorded at the Cape Leeuwin station.
"But this signal was not detected at the Diego Garcia station. This raises questions about its origin."
Researchers have proposed a series of controlled underwater explosions or air gun fire along the Seventh Arc to see whether they can isolate a more precise location for MH370.
"Similar exercises were performed in the search and rescue mission for the ARA San Juan, a submarine that vanished off the coast of Argentina in 2017," Dr Kadri added.
"This shows us that it is relatively straightforward and feasible and could provide a means to determine the signal’s relevance to MH370, prior to resuming with another extensive search.
"If found to be related, this would significantly narrow down, almost pinpoint, the aircraft’s location.
"On the other hand, if the signals are found to be unrelated, it would indicate a need for authorities to reassess the time frame or location established by their official search efforts to date."
The lost flight remains one of the world's biggest aviation mysteries - with the official narrative suggesting it was ditched somewhere over the Southern Indian Ocean with all on board presumed dead.
It is feared the aircraft's pilot - Captain Zaharie Ahmad Shah - may have purposefully crashed the plane in a chilling mass murder-suicide.
Brit Boeing 777 pilot Simon Hardy believes the clues to this theory are buried in the flight documents.
He told The Sun how the addition of extra fuel and oxygen, as detailed in the logs shown above, could be proof that the plane's disappearance was premeditated.
Hardy's hypothesis that caught the attention of the official MH370 search team.
He calculated the most likely position of the remains of the doomed flight.
And he was invited to join the search with the Australian Transport Safety Bureau (ATSB) in 2015, where a team of experts were leading the hunt.
But his calculations put the resting place for the plane just outside the official search area - and despite consulting on the operation, he never had the chance to prove his theory.
He suggests the plane's pilot would have been in control the whole time - attempting to neatly plunge the plane into the ocean so it could never be found in a spot known as the Geelvinck Fracture Zone.
Boeing pilot Simon also spoke in depth about bizarre additions to the flight before it "headed to oblivion".
The plane's technical log shows that the cockpit's oxygen levels were topped up - despite them not being low.
Another document of note is MH370's operational flight plan.
It which shows that an extra 3,000kg of fuel was added to the plane - the maximum amount of extra fuel that can be added to a Boeing 777 flight.
The fuel would have given the pilot 30 minutes more flying time or more importantly, Simon explains, more time to ditch the plane in the ocean in daylight.
The official narrative suggests the plane made a bizarre U-turn, flying across Malaysia, turning northwest at Penang Island, and across the Andaman Sea after being tracked by military radar.
Data from the Inmarsat satellite communications network revealed that the plane then flew until at least 8.19am, travelling south into the Southern Indian Ocean.
On March 24, the Malaysian Government concluded that "Flight MH370 ended in the Southern Indian Ocean" - but several searches have been unsuccessful in recovering the wreckage.
Only a few pieces of debris were ever found, one being the plane's flaperon after it washed up on Reunion Island.
After it was studied by experts in France, it was determined that the flaperon was in a downward position.
This means the plane's flaps would have been down when it plunged into the ocean, Simon explains.
