MH370: experimental ocean blasts could bring investigators closer to the truth

By Annette Gartland on June 22, 2024

This article has been updated.

Scientists who have been studying acoustic signals to see if they might have come from the missing Malaysia Airlines flight MH370 say field experiments in the southern Indian Ocean involving controlled explosions or airguns could help bring investigators closer to the truth of what happened to the plane.

Usama Kadri (pictured left), who is an interdisciplinary theoretician, applied mathematician, and aerospace engineer, affiliated with Cardiff University, has been analysing signals captured on underwater microphones (hydrophones) and detected at the Comprehensive Nuclear-Test-Ban Treaty Organization’s (CTBTO) hydroacoustic monitoring stations off Cape Leeuwin in Australia and on Diego Garcia, an island in the Indian Ocean.

Significant media attention has focused on Kadri’s discovery of a signal detected at the Cape Leeuwin station.

The signal in question was generated on the day of MH370’s disappearance within a few minutes of the last satellite ping the British company Inmarsat says was received from the plane along what is known as the 7^th Arc. The signal was not detected at Diego Garcia.

“This raises questions about its origin, but it could be just noise as it was not picked up by Diego Garcia’s hydroacoustic station,” Kadri said. “We also examined data for signals along MH370’s initial flight path but found no corresponding acoustic signatures.”

Both the Cape Leeuwin station and the one on Diego Garcia were operational at the time the signal was generated, Kadri says. Both stations are located within tens of minutes’ signal travel time from the 7th arc.

Kadri is eager to emphasise that the signal in question has not been identified as coming from MH370. He says the signal, which was relatively weak, came from the direction of the 7^th Arc and coincides, time-wise, with a signal coming from the Antarctic.

“There is currently no signal that we can say is associated with MH370,” Kadri told Changing Times.

Alec Duncan, who is a senior research fellow at Curtin University in Perth, Australia, explains that the Diego Garcia hydroacoustic station has two hydrophone arrays, one north of the island and one to the south.

“The northern array wasn’t functioning on March 8, 2014, but the southern array was fully operational,” Duncan said. “However, there were several offshore seismic surveys going on at the time, which produced frequent, loud signals from their airgun arrays that obscured all but the strongest arrivals at the southern station from other sources.”

The distance from the 7th arc to the Cape Leeuwin station is about 1,600 kilometres and the distance to Diego Garcia is about 3,700 km.

The 7th arc was defined early on in the search for MH370 and is based on calculations by Inmarsat that were based on satellite pings – or handshakes – from MH370. Inmarsat said that MH370 was most likely to be found along this 7th arc.

There are investigators who doubt the validity of the Inmarsat data and believe that MH370 never reached the southern Indian Ocean. Others continue to have faith in the data, but some question the deductions that have been made.

Flight MH370 went missing on March 8, 2014, with 239 passengers and crew on board. It was en route from Kuala Lumpur to Beijing.

While some debris has been found that the Malaysian authorities say is from the missing plane, neither MH370 nor its voice and data recorders have been located.

Previous analysis by scientists at Curtin University and later by a team led by Kadri confirmed a signal of an unknown source recorded at Cape Leeuwin station in the direction of the 7th arc, but it fell outside the time window suggested by the official MH370 investigators.

Kadri’s latest research focused on the official, narrower time window. This analysis identified only one relevant signal in the direction of the 7th arc. It has a bearing of 306 degrees relative to the Cape Leeuwin station, hence Kadri refers to it as ‘Signal 306’.

An article about Kadri’s most recent research was published last month in Scientific Reports. More than 100 hours of data, captured by hydrophones after ten aircraft accidents and one submarine disappearance, were analysed for the study.

“Violent ocean impacts such as airplane crashes produce distinctive acoustic signatures which travel vast distances through the water and are recorded by hydrophone technology from various locations on the seabed,” Kadri explains.

Kadri recommends conducting field experiments involving controlled explosions or airguns along the 7th arc while monitoring the signals received at surrounding hydroacoustic stations.

He says that these field experiments should help identify where to search for MH370, and where not to search. “We would be able to see if there is anything that was overlooked that resulted in miscalculations.”

The experiments could be done in various ways, Kadri says. “The fastest would probably be by a government’s navy. They could also be conducted by a research vessel, though this could take a much longer time to conclude,” he said.

The third option, Kadri says, is making use of vessels that are passing by the 7^th Arc, for example oil and gas ships equipped with airguns – as has been suggested by Kadri’s colleagues and experts in the field.

One possible result of the field experiments is that the explosions or airgun shots yield no signal (nothing recorded at the Cape Leeuwin station or Diego Garcia). This is unlikely, though possible, Kadri says, as there have been recordings over a much longer distance. However, the parameters in the ocean are much more than just distance, he adds.

“If we run the experiments and we record nothing at the two stations, we cannot rely on the available hydrophone data to assist for the search,” Kadri said.

If the experiments yielded strong signals that were picked up at both Cape Leeuwin and at Diego Garcia then the official investigation should be revisited, Kadri says.

“This would mean they would have to revisit their assumptions and calculations to find an updated time-window and location,” he said.

The third possibility, which Kadri says is potentially the most realistic, would be a combination result: some strong signals being picked up at some locations and none at others and some signals picked up at Cape Leeuwin, but not at Diego Garcia. “This would give us more than a hint on what to exclude and what to include,” Kadri said.

“If an experimental blast gave a strong signal from a particular area that was picked up at Cape Leeuwin and Diego Garcia, but there was no acoustic signal that could possibly be from MH370 in that area, then the plane must not be there. If it was there we would expect to see a strong signal too.”

Kadri hopes that the field experiments he suggests can be done before the next search for MH370, proposed by the American seabed exploration company Ocean Infinity, begins.

He already has collaborators who are, in advance of the proposed field experiments, conducting numerical experiments (simulations on computers).

The field experiments are the most important, however, Kadri says. “You can’t argue with the field experiments whereas, on the computer, you start simplifying things in order to be able to run the computations in a realistic time frame,” he said.

Kadri says there are many possible reasons why ‘Signal 306’ was not picked up at the Diego Garcia station. It could, for example, be because of a localised event such as an exploration vessel, close to the Cape Leeuwin station, dropping an object into the water.

“We don’t know what the signal really looks like as it is buried in ambient noise. It was in the direction of the 7^th Arc, but, in this scenario, it would have been too far away from Diego Garcia to be picked up.”

Such scenarios are a reason why Kadri doesn’t share the excitement exhibited in mainstream media outlets about ‘Signal 306’.

The focus, Kadri says, should be on the field experiments. “The focus should be on trying to have a little bit more data, a little bit more patience … trying to understand a little bit more, do some careful analysis, and then make a focused search in a narrower area,” he said.

“With the current data, we don’t know where MH370 is. From my point of view, it could be anywhere.

“The question is how we can go one step forward towards the truth. I think the field experiments can help us step forward towards the truth.”

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, Kadri says. However, unfavourable ocean conditions could potentially dampen or obscure such a signal.

One of the problems Kadri faces is that he cannot recognise whether an acoustic signal is from a plane. “If we see a signal coming from a whale, experts will tell you that’s a whale. If there’s a signal from an earthquake, experts will tell you that’s an earthquake. The problem with airplanes is that, first of all, the duration of the event itself is very short … a few seconds.

“We don’t have an understanding of the uniqueness of a signature coming from an airplane crash. When I see a signal in the data, I can’t say that’s an airplane. We simply don’t have that knowledge.”

Alec Duncan cautions that further analysis should be carried out before taking any action based on ‘Signal 306’. He says it’s possible that, in the analysis of this detection, Kadri’s software may have misinterpreted some of the residual energy from strong signals coming from the south at the same time (most likely Antarctic ice-cracking events) and arriving at the Cape Leeuwin station at the same time as ‘Signal 306’.

In his analyses, Duncan has not identified any signals coming from the direction of the 7^th Arc. All the signals he has identified in the time window in question have originated in the south and were almost certainly ice-cracking events.

He told Changing Times: “There are relatively few places in the Indian Ocean where an aircraft could have crashed that would have resulted in a detectable sound being received at the Cape Leeuwin hydroacoustic station.

“This is because most of the sound from a surface impact initially travels steeply downwards, which prevents it from getting trapped in the deep sound channel and travelling long distances.

“For the sound to get into the deep sound channel the impact would have to occur in water that wasn’t too deep (very roughly, not more than 3,000 metres) and where the seafloor was sloping downward towards the receiver.”

Duncan agrees with Kadri that it would be a good idea to conduct calibration explosions along the 7^th Arc.

“Given the time and expense involved in just getting a suitable ship out to the 7^th Arc it would make sense to do this at as many locations as the budget allows, starting at a place that is thought most likely to be the MH370 crash site,” Duncan told Changing Times.

The source of the explosion would need to be a near-surface source, Duncan said. “You’d get a completely different answer if you put a source down a few 100 or 1,000 metres. You’d get much stronger signals at Cape Leeuwin than you would if the source was at 10 metres.

There’s a need to determine how the likelihood of detecting a signal at long range varies with the depth of the source, which would require multiple transmissions from at least one location, Duncan says.

He adds: “Water column properties change with latitude so detection results would also be expected to vary with latitude. Seafloor shape and properties can also have an effect.”

The kind of field exercise Kadri and Duncan are recommending was performed in the search for the ARA San Juan, an Argentine Navy submarine that vanished off the coast of Argentina in 2017.

A few hours after the submarine disappeared, an unusual signal was recorded by CTBTO stations. To help with the search, a calibration grenade drop was conducted two weeks later near the submarine’s last known location.

The calibration grenade, which was also recorded at the CTBTO hydroacoustic stations, was similar to the unusual signal that radiated from the submarine implosion. The submarine was found a year later by Ocean Infinity.

In 2018, Ocean Infinity spent more than three months searching for MH370 in the southern Indian Ocean. The company scoured, and collected data from, more than 112,000 square kilometres of ocean floor, which is far in excess of the initial 25,000-square-kilometre target and almost the same area as was examined in the previous search over a period of two and a half years.

The previous Australian-led underwater search for MH370 was suspended on January 17, 2017, after an area spanning 120,000 square kilometres was scoured.

In May this year, Ocean Infinity made a presentation about its new ‘no find, no fee’ search proposal to Malaysia’s Minister of Transport, Anthony Loke, senior transport ministry officials, and representatives of other government agencies.

Loke said the matter would need to be presented to the Cabinet before an agreement was finalised and he anticipated that the process would take about three months to complete.

V.P.R. Nathan (left), whose wife, Anne Daisy, was a passenger on MH370, presents Ocean Infinity’s new proposal to Anthony Loke during the MH370 10^th anniversary remembrance event in Kuala Lumpur.

Reports about Kadri’s research can be found here, here, and here.