Twelve years after Malaysia Airlines' MH370 vanished, an overlooked clue is back in focus

MH370 overlooked clue: Twelve years after Malaysia Airlines flight MH370 disappeared, an old acoustic clue is raising fresh questions about whether investigators may have spent years searching in the wrong part of the Indian Ocean.

The Boeing 777 vanished on March 8, 2014, after its transponder stopped identifying the aircraft on civilian radar. But the plane continued communicating with an Inmarsat satellite for several hours. Timing and frequency data from those contacts suggested that MH370 had flown south into the Indian Ocean before ending near a curved line of possible locations known as the “seventh arc,” as per a report.

Search teams spent years looking for the wreckage there. They found nothing. That has renewed interest in another possible source of evidence: underwater sound.

Could hydrophones have detected the MH370 crash

Hydrophones are underwater microphones that record sounds travelling through the ocean. Researchers believed they might have detected the impact of a large aircraft hitting the water, as per a Popular Mechanics report.

The CTBTO's global hydroacoustic network initially became a focus. Its hydrophones can record sounds over vast distances, and there was already evidence that such data could help locate objects beneath the sea.

In 2017, CTBTO stations detected an unusual underwater signal near the last known position of Argentina's missing submarine ARA San Juan. The wreckage was found the following year.

A large aircraft crashing into the ocean should also have created an acoustic signal. A 2024 study by Cardiff University researcher Usama Kadri found that sound from previous aircraft crashes at sea had travelled between 2,000 and 5,000 kilometres through the water, as per the Popular Mechanics report.

But researchers studying CTBTO data found no convincing signal near MH370's presumed crash area along the seventh arc.

Instead, a low-frequency signal recorded west of Rottnest Island appeared to point far to the northwest, near the Chagos-Laccadive Ridge.

The simplest explanation was an underwater earthquake or another natural event. But one researcher believes it could have been something much more important.

An overlooked hydrophone network recorded the Indian Ocean

French researcher Royer's OHASISBIO network had been recording low-frequency sounds across the southern Indian Ocean since 2010, as per the Popular Mechanics report.

The instruments were not designed to search for missing aircraft. They were built to study small earthquakes and seafloor spreading, while also recording whale calls.

Unlike the CTBTO network, the hydrophones stored recordings internally and had to be recovered before the data could be analysed.

MH370 disappeared only weeks after the instruments were deployed.

When the network was recovered in early 2015, one of the hydrophones closest to MH370's presumed crash area was lost. But the remaining instruments survived.

Royer later identified five possible acoustic events around the time MH370 disappeared. Two had already been identified in earlier CTBTO-based research.

He sent his analysis to French and Australian officials in late 2016, but it was not included in the ATSB's final search report published the following year.

Royer believes officials may have considered the work too similar to earlier CTBTO analysis, as per the Popular Mechanics report. Still, the independent recordings showed that separate hydrophone networks had detected some of the same events.

Could MH370 have crashed somewhere else

The acoustic evidence does not overturn the satellite analysis. But it adds to the growing list of questions surrounding the official search area.

MH370 debris confirmed that parts of the aircraft reached the western Indian Ocean, but drift models struggled to explain every fragment's journey. Meanwhile, years of seabed searches found no wreckage.

Between 2014 and 2017, the Australian-led search covered more than 120,000 square kilometres of seafloor. Ocean Infinity's 2018 search brought the total area searched close to 200,000 square kilometres.

By March 2026, the company said it had mapped more than 140,000 square kilometres of seafloor since returning to the search, but still had not found the aircraft.

Ocean Infinity CEO Oliver Plunkett said, “If nothing else, we can say with confidence that it isn’t where we looked,” as quoted by Popular Mechanics.

David Dall'Osto, a senior research scientist who has worked on CTBTO hydroacoustic data, believes the unexplained signal in the northwest Indian Ocean could be the acoustic signature of MH370's impact.

If he is right, the search may have been focused on the wrong location for 12 years. Dall'Osto said, “There was a sound that was made right there,” adding, “It’s not like it was made along some 6,000-mile-long arc. It was made at this spot right here,” as quoted by Popular Mechanics.