New Hydroacoustic Data!

New hydrophone data, collected on the day MH370 disappeared and never before released, sheds new light on whether and where the plane impacted the surface

In 2014, a French marine researcher named Jean-Yves Royer came to an exciting realization. A senior scientist the French government research organization CNRS, he had spent years setting up and running a network of sensitive underwater microphones, or hydrophones, that picked up the sounds of seabed earthquakes and migrating whales in the southern Indian Ocean. Now, he realized, it had the opportunity to do much more than that. It could help solve one of the world’s most famous and vexing mysteries by pinpointing the resting place of a Malaysian airliner, MH370, that had gone missing that March with 239 souls on board. There was one catch: he’d have to wait until the buoys finished collecting their data and popped to the surface, almost a year in the future. Once that happened, Royer could download the data, find a loud noise that matched the time of the plane’s impact, and triangulate the location of the wreckage.

But it was not to be. After Royer submitted his data to French and Australian authorities, they sat on it, neither releasing it to the public nor issuing it as part of a accident report. The data remained buried.

Until now. Prompted by an inquiry from a viewer, I reached out to Royer and he agreed to share his long-buried report. (You can view it yourself here.) In a mystery that is puzzlingly lacking in physical clues, this is evidence that meaningfully constrains what might have happened to MH370.

Coming on the heels of Malaysia’s recent announcement that it has extended its seabed-search agreement with the marine survey company Ocean Infinity for another year, the release of Royer’s findings raises the prospect that, in the event that that final seabed scan is unsuccessful, investigators might need to contemplate a radical rethink of their assumptions.

ROYER WASN’T THE only one who saw that hydrophone data could hold the key to solving the mystery. The Australian Transport Safety Board, or ATSB, which is charged with finding the plane, has long been aware that hydroacoustic data could fill in the gaps in the case’s all-too-scant evidence.

When MH370 vanished in the early morning hours of March 8, 2014, it first went electronically dark, then started transmitting satellite communications signal in an unusual configuration that implied that someone had tampered with its electrical system in a sophisticated way. The signals themselves carried no information — no texts or voice data — but the signal metadata offered subtle hints that the plane had flown to a particular region of the southern Indian Ocean. There, somewhere above a curved section of ocean dubbed the “7th arc,” the plane had run out of fuel and crashed. When investigators scanned that area of the seabed, however, no trace of the wreckage was found.

Investigators hoped that sound data could resolve the mystery. Their attention focused at first on a network of hydrophones maintained by a group called the Comprehensive Test Ban Treaty Organization, or CTBTO, which since the early 2000s has been listening for evidence that someone with nuclear aspirations has detonated an A-bomb. Its buoys are anchored in the seabed and float in a layer of ocean water called the SOFAR channel, for “sound fixing and ranging.” Unlike water near the surface of the ocean, where sound might only travel for a few miles, the acoustic properties of the SOFAR channel mean that sounds can propagate for thousands of miles. As a result, the 6 hydrophone stations of the CTBTO network can detect underwater noises originating anywhere in the world.

There’s a precedent for using hydroacoustic data to solve a seabed mystery. In 2017, the Argentine submarine ARA San Juan vanished while at sea 270 miles off the country’s Atlantic coast. Working from the sub’s last known location, investigators scanned the seabed but found nothing. Then investigators turned to data from the CTBTO network. Two of the network’s hydrophones — one 4100 miles away, the other 4800 miles — had detected a noise that could be interpreted as the sound of a sub hull imploding. Triangulating from the time of arrival at each hydrophone, investigators were able to determine where the implosion’s location. In November, 2018, a year after the sub disappeared, a robot submersible operated by the marine survey company Ocean Infinity found the wreckage on the seabed.

A sinking sub is different from a crashing airplane, but hydrophones should have been able to pick up MH370’s final moments, as well. Analysis of MH370’s satellite transmissions had previously suggested that the plane was in a steep and accelerating dive at the moment it sent its final signals. Such a descent would have resulted in a high-speed impact. The fact that fragments of the interior cabin were later found by beachcombers also suggests a high-energy crash. The colossal boom that resulted should have been picked up the hydrophone network.

In 2024, researcher Usama Kadri at the University of Cardiff in the UK published a paper in the journal Scientific Reports in which he analyzed other cases where planes crashed in the ocean. He found that planes known to have impacted the water at high speeds had created sounds that were detected up to 3000 miles away, even low-speed impacts were detected at range of up to 2300 miles. Given that MH370’s presumed crash zone was just 1,000 miles from the nearest hydrophone, “one expects a significant signal to appear,” Kadri writes.

But when researchers at Curtin University in Perth, Australia analyzed the CTBTO data, they found that none of the hydrophones detected any sound that could have been made by the crash of mH370. The most plausible candidate was a low-frequency rumble that was recorded by a hydrophone set off the coast of Western Australia at 1:34 Universal Time, 15 minutes after the plane’s last satellite transmission. The same sound was also detected by another hydrophone station at Diego Garcia. “When you measure it in multiple places, you can identify the position,” says David Dall’Osto, a senior research scientist at the University of Washington Applied Physics Laboratory who has worked on the CTBTO hydroacoustic data. “It’s in the northwest Indian Ocean.”

The source turned out to lie near a geologically active underwater feature called the Carlsberg Ridge, southwest of India, thousands of miles from the 7th arc. That meant it couldn’t have been MH370; more likely, it was an underwater earthquake.

The fact that the CTBTO hydroacoustic array detected no trace of MH370 near the 7th arc doesn’t necessarily mean that the plane didn’t crash there. While a high-speed impact would almost certainly be detected, a low-speed ditching might not be. “A ditching like the Miracle on the Hudson is a much quieter event,” says Robert Parker, the former US Navy intelligence officer who turned me on to Royer’s work. “You’re definitely not going to get any sound going into the deep sound channel from that.”

IF THE CTBTO data proved inconclusive, then the addition of more hydrophones might be able to resolve the issue. And that’s exactly the opportunity that Royer’s data offers.

OHASISBIO, a French acronym that means “Hydroacoustic Observatory of Seismicity and Biodiversity,” was first deployed in the Indian Ocean in 2010. “We were interested in detecting small earthquakes that tell us about the dynamics of seafloor spreading,” Royer explains. “And since we are recording low frequency sounds, we also record calls from the large whales in different places and then figure out their migration pattern.”

Unlike the CTBTO array, the OHASISBIO hydroacoustic network is entirely focused on the southern Indian Ocean. All eight of its buoys were deployed there, as opposed to just two of CTBTO’s 6 hydrophone stations. That gave it the potential to hear more events and triangulate them more precisely. But it had a drawback. Instead of streaming data continuously back to the surface for immediate analysis, as CTBTO’s array does, OHASISBIO buoys are designed to record the information in internal storage, then periodically detach from their anchor and float to the surface, where they’re retrieved so that their data can be downloaded.

MH370 disappeared in March of 2014. The OHASISBIO buoys were scheduled to be collected the following January and February. That meant that Royer’s team had to wait nearly a year to see if their sensors had found the missing plane.

Finally, the research vessel Marion Dufresne went to collect the buoys — but bad luck intervened. As pickup was underway for the hydrophone called Northeast Amsterdam, the captain misjudged his timing and wound up running over the buoy as it bobbed to the surface. “He goofed,” Royer says. “The instrument went into the propellers of the ship and was chopped to bits and pieces.”

Unfortunately, this was the buoy positioned closest to the presumed crash site, and so would have had the best chance detecting an impact near the 7th arc. All of the other buoys, however, were retrieved successfully, and in total the recovered data set provided a much more comprehensive assessment of the Indian Ocean sound environment than the CTBTO array did on its own. In all, Royer identified five events that occurred in the Indian Ocean around the time of MH370’s disappearance, two of which had previously identified from CTBTO data.

Royer finished writing up his analysis in December of 2016 and submitted it to both French and Australian MH370 investigations. Australia’s ATSB published its final assessment of the MH370 disappearance the following year in a document called “The Operational Search for MH370.” Three of its ten appendices were devoted to the analysis of hydroacoustic data, but Royer’s findings were not among them. Royer thinks that the ATSB left out his report because they felt his findings were not different enough from the earlier Curtin University analysis to merit separate inclusion: “It didn’t bring any any new information relative to the CTBTO data,” Royer says.

That’s not really true, though. While Royer’s hydrophones didn’t detect any impact near the 7th arc, they did record the event southwest of India, and also confirmed another CTBTO-detected event linked to calving icebergs in Antarctica. In scientific terms, such duplication isn’t merely redundant; it adds weight to the validity of the earlier analysis and underscores the sensitivity and accuracy of both networks.

The fact that MH370 left no detectable acoustic trace of a crash in the 7th arc search area does not, on its own, necessarily undermine the satellite data analysis that says it must have gone there. But the absence of a hydroacoustic detection begins to seem more problematic when lined up alongside all the other kinds of evidence that should be there but aren’t. The authorities, for instance, were never able to generate a drift model that could explain how all the pieces of MH370 debris got to their discovery locations at the correct time. Nor did any of those objects carried traces of marine life that matched how long they had supposedly been at sea. And then, of course, most glaringly: an exhaustive, years-long sidescan sonar search of the seabed around the 7th arc came up empty. “If nothing else, we can say with confidence that it isn’t where we looked,” wrote Ocean Infinity CEO Oliver Plunkett after the company announced the end of its search effort in March of this year.

Could investigators have gotten something wrong? Was there something important in their analysis that they had overlooked? Suspicions have long simmered. In the very first Curtin University paper, written in mid 2014, the authors speculated that the absence of any detectable acoustic event near the 7th arc could mean that “there is a problem with the position line determined from the satellite handshake data.” In other words, that the satellite-data analysis could be wrong.

Today, hydroacoustic scientist David Dall’Osto still harbors doubts. “I agree with Dr Kadri that if the airplane crashed, it could have made a sound loud enough to be heard,” he says. “And if it was detected, it wasn’t on the seventh arc.” He thinks that the sound that came from southwest of India could be the acoustic signature of the plane’s impact. If that’s true, then it means that for the last twelve years investigators have been searching in the wrong place.

In a statement to the media on June 29, Malaysian officials announced that they would extend the no-find, no-fee search deal that Ocean Infinity seemed to have given up on in March. Based on the availability of Ocean Infinity’s marine survey ships, the next phase is most likely to take place some time between this November and April, 2027.

If that search comes up empty, too, Dall’Osto suggests that it might be time to throw in the towel on the 7th arc and move on to the seabed near India. “There was a sound that was made right there,” he says. “It’s not like it was made along some 6000-mile-long arc. It was made at this spot right here.”