The search in the Indian Ocean for the wreckage of the aircraft has been the largest and most expensive search effort in history - but it has turned up nothing.

Now, a team of researchers says Malaysia Airlines Flight 370 may have crashed thousands of miles from the search locations, based on sounds recorded in the ocean near the time the passenger jet disappeared on March 8, 2014.

In research published on January 29 in the open-access journal Scientific Reports, applied mathematician Usama Kadri said underwater microphones in the Indian Ocean had recorded four distinctive sound events, caused by very low-frequency acoustic-gravity waves, around the time that Flight 370 could have crashed into the sea.

His research showed that one of those sound events happened relatively close to the search area - but two others are thousands of miles away, in the northern part of the Indian Ocean, somewhere between Madagascar and the atoll of Diego Garcia in the Chagos Archipelago, Kadri told Live Science.

Investigators suspect that the lost airliner crashed somewhere in the Indian Ocean, although its flight path after it disappeared from civilian and military radars, west of the Malay Peninsula, is not known.

The aircraft's captain, Zaharie Ahmad Shah, had ordered enough fuel for a routine flight from Kuala Lumpur, Malaysia, to Beijing, a flight that would have lasted 7 hours and 30 minutes. But just how long the Boeing 777 jet could have stayed airborne would depend on its actual flight path, its altitude and how many of its four engines were operating.

Ocean sounds

Kadri and colleagues at the University of Cardiff in the U.K. and Memorial University of Newfoundland in Canada analyzed sounds recorded by a network of underwater microphones (called hydrophones), which are maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to listen for banned nuclear tests.

The CTBTO hydrophones give directional bearings, loudness and frequencies of sounds in the ocean, from which scientists can calculate an approximate location for where those sounds originated.

But the CTBTO hydrophone network is designed to detect underwater nuclear explosions, in concert with other monitoring systems in the air and through seismological tremors in the earth - and it was thought not able to detect a crashing jet.

To learn more about the patterns of sounds made by objects crashing into the ocean surface, Kadri and his colleagues recorded the sounds caused by weighted spheres impacting tanks of water in 2017.

They found that when a massive object like an airliner crashes into the ocean, it creates a distinctive pattern of sound waves — including patterns of very low-frequency sounds known as acoustic-gravity waves that can be transmitted for thousands of miles through the ocean.

Search at sea

Kadri said that future searches for any wreckage of the airliner should start with scientific investigations of the sound events recorded in the Indian Ocean - without regard to information from other sources, such as the satellite radio data, which could create large inaccuracies.

"All the efforts that were done before, they all relied on the satellite data as given evidence … unfortunately, they found nothing," he said.

Details of the new research had been relayed to the Malaysian and Australian authorities responsible for locating the aircraft, but there are currently no plans to resume the search at sea, Kadri said.

LiveScience.com