S2Ep6 Listening for MH370

A hydrophone network detected something. Was it the missing plane?

In 1892 Sir Arthur Conan Doyle published a Sherlock Holmes story called “Silver Blaze,” about the murder of a race horse’s trainer.  At a crucial juncture in the mystery Holmes realizes that no one has mentioned hearing the watchdog bark during the night.

A Scotland yard detective says, “Is there any other point to which you would wish to draw my attention?”

Holmes answers: “To the curious incident of the dog in the night-time.”

A character named Gregory says: “The dog did nothing in the night-time.”

Holmes says: “That was the curious incident.

Aha! You see, if the perpetrator of the murder had been a stranger, the dog would have barked, and people would have heard it. But no one heard it, so the dog didn’t bark, so the perp wasn’t a stranger.

The reason I’m talking about this is because it’s June 2024 and I’ve recently come across a bunch of stories suggesting that new evidence has emerged in the case. Like this one from the New Straits Times, with the headline: “Loke: Ocean Infinity's proposal to resume MH370 search will consider new lead by UK researchers”

This is about Malaysia’s Transport Minister Anthony Loke, and the “new lead” he’s talking about is a paper published by a researcher at Cardiff University in the UK named Usama Kadri.

Called “Underwater acoustic analysis reveals unique pressure signals associated with aircraft crashes in the sea: revisiting MH370,” the paper is published by Nature, a prestigioius journal. So on the face of it, it’s worth taking seriiously.

It’s a fascinating paper, and today’s episode of Finding MH370 I walk through the evidence that Kadri analyzed and what it might tell us about where MH370 ended up. The core question I’ll be addressing is this:  if a plane falls into an ocean, should we expect to hear it? Or, like a dog that doesn’t bark, should the absence of a noise be evidence that something DIDN’t happen?

It all goes back to 1945, when the United States detonated the first atomic weapons and set of a nuclear arms race. In the years that followed, the US, China and Russia all detonated test bombs in the atmosphere, then later limted their test explosions to underground detonation.

Eventually The UN adopted the Comprehensive Nuclear Test Ban Treaty in 1996. Technically, it isn’t in force, because the US never signed it, but essentially it’s being followed. Though Pakistan, India and North Korea have all exploded A-bombs since then. Neverthelesss, an organization called the Comprehenisve Test Ban Ttreaty Organization, or CTBTO, monitors adherence to the treaty by maintaining a whole bunch of detectors around the world that try to detect seismic waves or radioactive particles and so forth.

A part of this network are 11 hydroacoustic stations dotted around the world’s oceans. They’re listening all the time, they’re quite sensitive, and so the question that Kadri explores in this paper is: should we expect the network to have detected MH370, and secondly, did it?

Kadri has a very elegant way to address the first question, which is to look at other plane crashes in the ocean, and see whether they were detected. I talk about a few of them in the episode, but to make a long story short, the hydrophone network is able to detect the sound of planes crashing into the ocean at distances of up to 5000 km.

In one case, the hydrophones detected a low-energy event — a ditching which both pilots survived — from 3,600 kilometers away.

The presumed crash site of MH370, meanwhile, lies a mere 1,600 km from the hydrophone array at Cape Leeuwin in Australia. Two other sets of hydrophones are 3,700 km away in Diego Garcia. So, really, all of them should have been able to detect MH370.

As Kadri writes, “It is highly unlikely for MH370 to have crashed near the 7th arc without leaving a discernible acoustic signature.”

OK, so was there an event?

The answer to that question is slightly complicated by the fact that the ocean is full of noise, so that, yes, noises were recorded by the hydrophone arrays, but when they were looked at closely — when the data was analyzed to determine the direction they were coming from — it turned out that most of them were simply not in the right place to have come from MH370.

One, however, strikes Kadri as being a potential match. He writes: “Within the specified time window, only a single signal of interest at a bearing of 306◦ has been identified.”

There’s some reason to doubt whether this noise came from the crash of MH370, however. Specifially, three:

1) The signal was only recorded at Cape Leeuwin. The distance from the event to Diego Garcia is about 3700 km, so the noise should have been picked up there as well.

2) The location of the sound’s origin is too far north. It’s actually on the northern edge of where Ocean Infinity searched, on the far, far fringes of where statistical analysis says it could plausibly be.

3) There’s a 17-minute discrepency between the time MH370 sent its final ping and the time the sound wave began propogating toward the Cape Leeuwin sensor. I find this problematic because as we saw in episode 4, if the plane was in the terminal dive indicated by the BFO data, it shouldn’t have been in the air for less than a minute.

When all these considerations are taken together, it appears that this signal lies on the far fringes of what’s possible.

So once again we have a situation in which, having found a new form of evidence to shed light on the disappearance of MH370, the new information fails to clearly reinforce the default scenario — that the plane was taken into the southern Indian Ocean as part of a mass murder/suicide plot by the captain. We saw the same thing that with the age and composition of the marine biofouling, the drift modeling, and so on.

If you squint and look at it sideways, you can just about convince yourself that there must be a perfectly reasonable explanation for the new data. But really, the simplest and most compelling interpretation is simply that MH370 didn’t fly into the southern ocean.

Kadri conclude his paper by suggesting that, since we can’t really make sense of this data, we need to gather more data. In this case he proposes calibrating the sound profile by detonating explosives along the 7th arc. The media coverage that his paper received tended to emphasize this part, suggesting that the results would allow us to better make sense of the acoustic signal and hopefull allow us to locate MH370, but honestly I don’t think that dog will hunt.

Or, if we’re talking about dogs, to say that the dog didn’t bark in the night-time.