Search Phase 2: Virgin Territory [S2Ep32 video]

The next phase of the search has been revealed, and it's got me feeling optimistic

In the last episode we talked about how we couldn’t tell what Ocean Infinity was planning, because they weren’t saying anything publicly and the ship tasked with searching the seabed seemed to be heading off to South Africa.

Well, fortunately, that didn’t happen. Instead, Armada 78 06 sailed to a stretch of ocean near the 7th arc, arriving there on Tuesday March 11, and it deployed its three search AUVs.

But what comes next?

With still no information coming out of Ocean Infinity or the Malaysia government, all we can do is read the tea leaves, and infer what their strategy is from the surface movement of the ship. There’s no getting around it: what we’re talking about is informed gueswork, but at least the picture is a lot clearer than it was a week ago. And basically, the news is quite good. In today’s episode I explain why.

You’ll remember that the first part of the seabed scan, which ran from February 23 to March 1, was conducted very close to the 7th arc and covered an area of the seabed that had already been scanned years before.

The theory was that, based on analysis of the Inmarsat data and aircraft performance, this was where the plane most likely went, and so the most likely explanation for why it hadn’t been found there was that against all odds it must have fallen into one of the very few places where the search data was incomplete due to technical glitches or rough terrain.

Well, that appears not to have been the case, because if Armada 78 06’s crew had found the wreckage they wouldn’t have to keep searching, which they are.

Since leaving port near Perth they’ve zipped themselves over to a different part of the ocean, about 100 nautical miles from where they were before. Since they’re looking in a different place they must be following a different analytical rationale. Let’s talk about what that could be.

One thing you’ll notice is that the area that they’re currently searching is outside both the original search carried out under the auspices of the Australian government between 2014 and 2017 and by Ocean Infinity in 2018. This is virgin terrain so it tells us that Ocean Infinity has given up the idea of searching data gaps, at least for now.

They’re looking quie far beyond the 7th arc. In fact the current position of the search vessel is about 55 nautical miles past the 7th arc. This is further than was previously deemed worth looking, because the odds that the plane could have gotten this far were deemed to be low. Why?

Some background: the scientists who studied the Inmarsat data came to the conclusion that the reason that the plane sent the ping that defined the seventh arc was that it had already run out of fuel and then a backup power system came online and restored power to the satellite data unit, which then sent that final set of signals.

Since the plane had already been without engine power for several minutes, and so would have already lost significant energy and altitude, reducing its ability to glide far from the 7th arc. On top of that, there are characteristics of the signal that indicate that it was in a steep and accelerating dive that would have put the plane into the ocean very, very quickly.

Back in Episode 4 of Season 2 we recreated what that dive would have looked like in a commercial 777 simulator. It’s over quite quickly. A plane that is traveling almost straight down for about a minute is not going to get very far at all from the 7th arc.

Yet it wasn’t found even with 35 nautical miles of the 7th arc. How can that be?

Well, either the scientists misinterpreted the Inmarsat data and the plane wasn’t really in a steep dive, or else after pushing the plane into this dive the pilot had a change of heart, perhaps deciding that he didn’t want to die that way after all, and pulled out of the dive and tried to glide as far as he could using his remaining speed and altitude.

How far could he get if he changed his mind after, say, 10 seconds of a near-vertical dive?

It’s hard to say exactly, because there are so many unknowable variables at play, but the absolute maximum that’s conceivable would be on the order of 100 nautical miles. Assuming he’s lost significant altidue during that steep dive, 70 is a more plausible upper bound. But the further you go outwards away from the 7th arc, the lower the probability gets. That’s way the first search was right on the arc, the second search was outward from that, and the third search appears to be searching outward from that.

So that’s why they’re searching this far away from the arc. But why are they searching on this spot, laterally along the arc? What’s the analytical basis for that?

You’ll recall that the first phase of the search was close to an area that Victor Ianello and his colleagues had identified based on Inmarsat data, aircraft performance, and drift modelling. But that’s not the only endpoint along the arc that you can plausibly make a case for. Every different combination of aircraft speed and direction will put the plane in a different place at the moment it sends that final transmission. You can try all kinds of ideas, and each will result in a different final location.

Reading the tea leaves, this is my best guess as to what Ocean Infinity is thinking. I think they’re going to scan another strip of seabed between 35 nautical miles and mayble 70 nautical miles away from the 7th arc, something a bit like the rectangle outlined in white:

For reference, this is about 37,000 square kilometers, substantially more than the 15,000 square kilometers that Ocean Infinity originally proposed to scan in total. Maybe this is just me being optimistic, but this is what happened during the last Ocean Infinity search in 2018—they searched way more than originally planned, and that makes sense, because if you’re going to go all the way out into the remote ocean you might as well go for it.

So I think there’s a good chance that they’ll do a nice long strip here on the outer edge of prior search zones, and if they don’t find it mabye they’ll do some more strips outward and inward from the 7th arc, maybe even beyond 70 nm away from the 7th arc. Given that they’re using a whole new generation of technology, I don’t think it would even take that long, though the ship might have to go back to port a time or two to refuel, resupply and take on new crew. Ocean Infinity could easily, I think, exhaust all plausible seabed search areas by June, if not earlier.

Of course, all that is pure speculation, and I say it with zero confidence; there is so much we don’t know about the company’s ideas and intentions. We don’t even know whether they think Malaysia is ever really going to sign that contract.

What do you think? What is your gut telling you? Let me know in the ongoing chat for this episode.