Jeff Wise

The website The Maritime Executive has a story up about an apparently successful bid by Russia to scramble GPS signals in the Black Sea–for reasons unknown:

An apparent mass and blatant, GPS spoofing attack involving over 20 vessels in the Black Sea last month has navigation experts and maritime executives scratching their heads.

The event first came to public notice via a relatively innocuous safety alert from the U.S. Maritime Administration:

“A maritime incident has been reported in the Black Sea in the vicinity of position 44-15.7N, 037-32.9E on June 22, 2017 at 0710 GMT. This incident has not been confirmed. The nature of the incident is reported as GPS interference. Exercise caution when transiting this area.”

But the backstory is way more interesting and disturbing. On June 22 a vessel reported to the U.S. Coast Guard Navigation Center:

“GPS equipment unable to obtain GPS signal intermittently since nearing coast of Novorossiysk, Russia. Now displays HDOP 0.8 accuracy within 100m, but given location is actually 25 nautical miles off; GPS display…”

After confirming that there were no anomalies with GPS signals, space weather or tests on-going, the Coast Guard advised the master that GPS accuracy in his area should be three meters and advised him to check his software updates.

The master replied:

“Thank you for your below answer, nevertheless I confirm my GPS equipment is fine.

“We run self test few times and all is working good.

“I confirm all ships in the area (more than 20 ships) have the same problem.” 

The article goes on to describe further details of the incident, and to note that hundreds of thousands of cell phone towers in Russia are equipped with GPS jamming devices as a defense against US missiles–and also that Russia has previously jammed GPS signals in Russia and in Ukraine.

Point being, we should not underestimate Russia’s capabilities when it comes to spoofing satellite signals.

In my last post, I reviewed Malaysia’s analysis of the MH370 debris its investigators have gathered. Not included in that study was the flaperon found on Réunion, as it is being held by the French. So today I’d like to look at what the damage patterns seen on the flaperon suggest about the crash, based on the work done by IG member Tom Kenyon and by a reader of this blog, @HB.

On February 3 of this year, Kenyon released an updated version of his report “MH370 Flaperon Failure Analysis” in which he gives an overview of the flaperon’s structure and how it was damaged. He notes that of the six main structural attachment points of the aircraft, the two biggest and most significant are the flaperon hinges (pictured above). They snapped in the middle:

The lesser attachment points failed in a similar way. That is to say, they did not rip away the flaperon structure to which they were attached.

Kenyon observes:

The location of the failure points of Flaperon hinges is consistent with a large singular lateral force or repetitive lateral (or torsional) movement of the hinges in the inboard/outboard direction. If Flaperon was separated from the Flaperon hinge with forces in forward/aft direction or by applying forces to the Flaperon in the extreme rotated up/down direction (beyond structural stops) then deformation of the Flaperon structure due to such forces would be evident. Significant and permanent deformation of the Flaperon structure does not appear to be present in photographs of the Flaperon.

Recall that two scenarios have been proposed for the flaperon coming off 9M-MRO: either the plane hit the water, or it came off as the result of flutter in a high-speed dive. Neither event could reasonably be expect to produce a primarily lateral (that is side-to-side) force on the flaperon of the kind Kenyon describes.

To raise the level of perplexity, Kenyon points out in other crashes involving 777s, failures didn’t occur at the hinges; rather, the hinges remained intact and the material to which they were attached broke. That is to say, hinges are stronger than the flaperon proper. Here’s an example from MH17:

Kenyon concludes that:

No significant evidence of secondary structural damage excludes a massive trailing edge strike and leads the author to conclude that the Flaperon separated from MH370 while in the air and did not separate from the wing due to striking water or land.

In other words, since the damage isn’t consistent with a crash into the sea, we can deduce that flaperon must have come off in the air. The only conceivable cause would be high-speed flutter. However, on closer inspection the evidence seems to rule out flutter, as well.

The reader who goes by the handle @HB is an expert in quantitative risk assessment in the transportation industry and has extensive experience with composite materials. In a comment to the last post, he observed:

For the flaperon… the lift/drag load is normally passed on the honeycomb panel over the exposed surface area then the primary stucture of the component (the aluminum frame of the flaperon) then the hinges then the primary aluminum stucture of the wing.

In a nut shell, those panels are not designed to sustain any in-plane loads either compressive or tensile. They are just designed to resist bending due to uniform lift load on the surface (top FRP layer in tension and bottom FRP layer in compression, the honeycomb is basically maintaining the distance between the layers without much strength).Those panels can arguably take a little bit of shear load due to drag forces on the top skin (top and bottom forces in opposite direction) but not much due to limits in the honeycomb strength.

The second thing to consider are the GRP properties. The GRP is very tough in tensile mode, much stronger than Steel. In compression mode, it buckles easily and only the honeycomb is preventing this. This is by far the weakest failure mode. If it fails, you will see fibres pulled out link strings on a rope failing under tension. For the skin under compression, you will see sign of compression on the honeycomb but the fibres will have to be pulled out as well. Also, a perfect manufacturing does not exist, there are always delamination (small bonding defects) between the honeycomb and the GRP skin to weaken further the compressive strength.

The hinges are usually much stronger as all the load is passing through them (analogy door hinges).

So you could imagine, if there is a large impact the hinges are expected to fail last. The part of the skin that will buckle is expected to fail first.

@HB here is agreeing with Kenyon: it is baffling that the flaperon came off the plane due to failure within the hinges. But @HB goes further, arguing that this type of damage is inconsistent with flutter:

I would tend to agree that the hinges have been subject to cyclic fatigue… the hinges appear to have been subject to cyclic lateral forces which are not expected in any accidental circumstances (take door hinges, for instance, and imagine the hinge fail after 50 times someone is trying to burst through – you can try at home but it is very unlikely to happen). This of course requires a closer look by experts to double confirm. I cannot think myself of any possible lateral force on this part in the first place but a lateral force that will fail the hinges and not the skin which is weaker is very hard to explain. Try with a wooden door and tell me if you manage.

In a followup comment, @HB observes that even under very strong oscillation the flaperon should not be expected to disintegrate. “If hydraulic power is on, fluttering is unlikely to cause any disintegration. If off, fluttering forces are up and down and the hinges are free to move. Lateral forces, I think, would be small in comparison with the vertical forces and not be strong enough to cause fatigue on the hinges.”

Kenyon concludes his report with a list of six questions and issues generated from his analysis. While all are worthwhile, one stands out to me as particularly urgent:

• Why are the official investigators silent on releasing preliminary reports on their Flaperon analysis? Why would France’s Direction générale de l’armement / Techniques aéronautiques (DGA) release photographic data to ATSB and yet chose not to make Flaperon Analysis findings public after such a long period of elapsed time?

To sum up, a close examination of the flaperon’s breakage points does not yield any comprehensible explanation for how it came off the plane, commensurate with a terminal plunge into the southern Indian Ocean.

This is baffling but unsurprising. Every time we look at the debris data carefully, we find that it contradicts expectations. The barnacle distribution doesn’t match the flotation tests. The barnacle paleothermetry doesn’t match the drift modelling. The failure analysis doesn’t match the BFO data. And on and on.

Something is seriously amiss.

Black box data is the ne plus ultra of aircraft accident investigation. But it is not the only kind of physical evidence. Pieces of debris—in particular, their dents and fractures — can tell a vivid story by themselves.

There are five basic ways that an object can break. The two most important for our present discussion are tension and compression. A tension failure occurs when something is pulled apart—think of pulling the ends of a piece of string until it snaps. Compression is the opposite; it’s what happens when something is crushed by a weight or smashed in an impact.

When a plane crashes, it’s common for all different parts to exhibit different kinds of failure. Imagine a plane whose wingtip hits a tree. The impact would crush the leading edge of the wingtip—compression failure—and then wrench the wing backwards from the body of the plane, causing a tension failure at the forward wing root and compression failure at the aft end.

By collecting many pieces of debris after a crash, investigators can place the mechanical failures in a chronological order to tell a story that makes sense, much as you might arrange magnetic words on a refrigerator. This is how the mystery of TWA 800 was solved. When the fuel tank exploded, the pressure pushed the fuselage skin outward so that it came apart like a balloon popping. The plane broke into two major parts that smashed apart when they hit the ocean. Thus tension failures predominated in the first phase of the catastrophe and compression failures predominated later.

So now let’s turn to the issue at hand. What story do the pieces of MH370 debris tell?

In April of this year the Malaysian government published a “Debris Examination Report” describing the 20 pieces of debris that were deemed either confirmed, highly likely or likely to have come from the plane. For 12 of them, investigators were able to discern the nature of the mechanical failure. Some key excerpts:

Item 6 (right engine fan cowl): “The fracture on the laminate appears to be more likely a tension failure. The honeycomb core was intact and there was no significant crush on the honeycomb core.”

Item 7 (wing-to-body fairing): “The fibres appeared to have been pulled away and there were no visible kink on the fibres. The core was not crushed; it had fractured along the skin fracture line.”

Item 8 (flap support fairing tail cone): “The fracture line on the part showed the fibers to be ‘pulled out’ showing tension failure. Most of the core was intact and there was no sign of excessive crush.”

Item 9 (Upper Fixed Panel forward of the flaperon, left side): “The fracture lines showed that the fibres were pulled but there were no signs they were kinked. The core was intact and had not crushed”

Item 12 (poss. wing or horizontal stabilizer panel): “The carbon fibre laminate had fractured and appeared to have pulled out but there was no crush on the core.”

Item 15 (Upper Fixed Panel forward of the flaperon, right side): “The outboard section had the fasteners torn out with some of the fastener holes still recognizable. The inboard section was observed to have signs of ‘net tension’ failure as it had fractured along the fastener holes.

Item 18 (Right Hand Nose Gear Forward Door): “Close visual examination of the fracture lines showed the fibers were pulled and there was no sign of kink.”

Item 20 (right aft wing to body fairing): “This part was fractured on all sides. Visual examination of the fracture lines indicated that the fibers appeared to have pulled away with no sign of kink on the fibers.”

Item 22 (right vertical stabilizer panel): “The outer skin had slightly buckled and dented but the inner skin was fractured in several places…. The internal laminate seems to be squashed.”

Item 23 (aircraft interior): “The fractured fibres on the item indicated the fibres were pulled out which could indicate tension failure on its structure.”

Item 26 (right aileron): “The fitting on the debris appeared to have suffered a tension overload fracture.”

Item 27 (fixed, forward No. 7 flap support fairing): “One of the frames was completely detached from the skin. It may be due to fasteners pull through as the fasteners’ holes appeared to be torn off with diameters larger than the fasteners.”

Note that all of these but one failed under tension. The exception is item 22, which came from the tail—specifically, from near the leading edge of the vertical stabilizer.

It’s particularly remarkable that Item 18, the nose gear door, failed under tension. (Image at top) If, as the Australian authorities believe, the plane hit the sea surface after a high-speed descent, this part of the plane would have felt the full brunt of impact.

 

Bill Waldock, a professor at Embry Riddle University who teaches accident-scene investigation, says that if MH370 hit the water in a high-speed dive, you would expect to see a lot of compression, “particularly up toward the front part. The frontal areas on the airplane, like the nose, front fuselage, leading edge of the wings, that’s where you’d find it most.”

I spoke to a person who is involved in the MH370 investigation, and was told that officials believe that that observed patterns of debris damage “don’t tell a story… we don’t have any information that suggests how the airplane may have impacted the water.” Asked what kind of impact scenario might cause the nose-gear door to fail under tension, it was suggested that if the gear was deployed at high speed, this could cause the door to be ripped off.

This explanation is problematic, however. According to 777 documentation, the landing gear doors are designed to open safely at speeds as high at Mach 0.82 — a normal cruise speed. The plane would have to have been traveling very fast for the door to have been ripped off. And to be deployed at the end of the flight would require a deliberate act in the cockpit shortly before (or during) the terminal plunge.

The experts I’ve talked to are puzzled by the debris damage and unable to articulate a scenario that explains it. “The evidence is ambiguous,” Waldock says.

In a blog post earlier this month, Ben Sandilands wrote, “Don Thompson, who has taken part in various Independent Group studies of the mystery of the loss of the Malaysia Airlines in 2014, says some of these findings support a mid-air failure of parts of the jet rather than an impact with the surface of the south Indian Ocean.”

A mid-air failure, of course, is inconsistent with the analysis of the Inmarsat data carried out by Australian investigators. So once again, new evidence creates more questions than answers.

UPDATE 5/24/17: Via @ALSM, here’s a diagram of the front landing gear and doors:

UPDATE 5/25/17: In the comments, we discussed the possibility that the front gear door could have come off in the process of a high-speed dive. @ALSM speculated that the loss of engine power upon fuel exhaustion could have led to loss of hydraulic pressure, which could have allowed the gear doors to open spontaneously, and then be ripped off in the high-speed airstream. But he reported that Don Thompson had dug into the documentation and confirmed that following a loss of hydraulic power the gear would remain stowed and locked. Thus it seems unlikely that the gear door could have spontaneously detached in flight, even during a high-speed descent.

UPDATE 5/25/17: There’s been some discussion in the comments about flutter as a potential cause of inflight breakup, so I thought it would be apropos to add a bit more of my conversation with the accident investigator involved in the MH370 inquiry.

Q: Does the MH370 flaperon look like flutter to you?

A: In a classic sense, no, but where you would be looking for flutter would be on the stops, on the mechanical stops that are up on the wing, so the part of that piece that came out. And in looking at that piece, you’ve got different types of failures of the composite skin that don’t appear to be flutter.

Q: What does it look like?

It just looks like kind of an impact-type separation. So it looks like you’ve drug that thing either in the water or on the ground or something. But it’s a little hard with that one because you don’t have any other wreckage, so, one of the keys — you don’t base anything on one small piece, you’re trying to look at kind of the macroscopic view of all the wreckage to make sure that, “Oh, if I think this is flutter do I see the signatures elsewhere on the airplane?” Typically we won’t base it on one piece like the flaperon.

To provide some context, we had earlier talked about the phenomenon of flutter in general:

Q: I can think of a couple of cases where there was flutter, where the plane got into a high speed descent and stuff got ripped off.

A: Yup.

Q: Where would that fall in the bestiary of failures that we talked about earlier?

A: So flutter’s kind of a unique thing, and it’s based on aircraft speed and structural stiffness. So, you know, when those two things meet you get this excitation, an aerodynamic excitation of a control surface which will become dynamically unstable and start going full deflection. So for a flutter case you generally look at the control stops—so there’s mechanical stops on all the flight controls—and you look for a hammering effect on the stops. So repeated impacts on the stop will tell you that, hey, maybe you’ve got a flutter event.

Q: But if you see the piece—there was a China Airlines incident, the elevator was shredded, or part of it was ripped off. What would that look like?

A: Mm-hmm. You know, it’s going to be different for every single case. Sometimes that flutter will generate the load in the attachment points, break the attachment points, and other times it will tear the skin of the control surface, and so you’ll see this tearing of the skin and the separation of rivet lines, and everything. I’ve seen both. I’ve seen a control surface that comes apart at the rivets, and flutters that way, and I’ve seen them where it generates loads to break the attachment points. It depends on the loads that are created and how they’re distributed throughout the structure.

For his part, Bill Waldock told me that the tensional failure of the collected debris implies a shallow-angle impact. Both experts, in other words, believe the debris is most consistent with a more or less horizontal (rather than high-speed vertical) entry into the water.

This is not consistent with the ATSB’s interpretation of the BFO data unless we posit some kind of end-of-flight struggle, à la Egyptair 990, or last-minute change-of-heart by a suicidal pilot. Either seems like a stretch to me.

Last month I wrote, in a post entitled “Nowhere Left to Look for MH370,” that recently refined drift models produced by Australia’s CSIRO contradicts both their own premise (that the plane crashed on the 7th arc between 34S and 36S) and an alternative idea presented by intependent researchers (that the plane crashed near 30S).

I’ve only just become aware that CSIRO director David Griffin weighed in on the matter a few weeks ago in a letter to Victor Iannello, which Victor published on his blog. He essentially confirmed the points I raised.

He wrote, for instance, that:

As you correctly pointed out, a 30S crash site would, according to our model, have resulted in debris washing up on Madagascan and Tanzanian shores a full year earlier than was observed. That is a discrepancy that is hard to set aside.

He also wrote that:

The other factor against 30S that we find very hard to discount is that 30S is right in the middle of the zone targeted most heavily by the surface search in 2014. This is the “other evidence” that Richard overlooked. Please see Section 4 of our Dec report, and Fig 4.2 of the April report.

Griffin also defends, rather weakly in my estimation, the idea that the early arrival of the “Roy” piece in South Africa does not contradict his preferred 34s-36S crash point. However, I don’t think this really matters, since there is so much other compelling evidence against it.

The conundrum, therefore, becomes even more impenetrable than before: the evidence indicates that the plane did not go into either of these “hot spots.” And it indicates even more strongly that it did not go anywhere else in the southern Indian Ocean.

The way to solve conundrums is to open up your thinking and to check for implicit assumptions that my be incorrect. In this case, the obvious follow-up question is: is it possible, given the data in hand, that the plane could have gone somewhere else?

Australian officials remain puzzlingly unwillingly to acknowledge the issue.

The suspension of the search for MH370 has been frustrating for many who care deeply about finding the plane. They feel that solving the mystery is essential not just for the emotional well-being of the passengers’ relatives but to protect the safety of the flying public. One group of MH370 relatives has gone so far as to raise money to fund a search on their own.

Assuming one were to raise the money, though, the question would then become: where to look?

Turns out, it’s not so easy to say.

Officially, of course, Australia says it knows where the plane most likely went. As I wrote in my last post, they’ve released a CSIRO report that uses drift modeling and other techniques to argue that the only plausible endpoint is on the 7th arc between 34 and 36 degrees south.

But as Victor Iannello points out in a recent post on his blog, there are some holes in the CSIRO’s logic. For one thing, according to their drift modeling, no-windage debris that enters the water at 35S will reach the shores of Western Australia in fairly significant quantities, but will not reach the South African coast by December 2015, when the real stuff started to turn up there. (You can play around with the kmz files that the CSIRO has made available online; say what you want about the Australians, they have been fabulous about explaining their work and making gobs of data available to the public.)

There’s another problem: the area between 34S and 36S has been searched out to 10 nm and beyond. I am very skeptical that a plane last spotted accelerating downward at 0.6 g, and already descending at 15,000 fpm, could possibly travel anywhere near as much as 10 nm. If anyone has produced flight sim runs that accomplish this, I would very much like to see it. (The IG said as much in their September 2014 paper.)

I’d add my own third reason to suspect that no wreckage would be found in the ATSB’s new search zone: it doesn’t play well with the DSTG’s Bayesian analysis of the BTO data, which is why it was excluded from the 120,000 sq km seabed search as it was ultimately defined.

So if not the ATSB’s new area, then where? South of 39.5S is ruled out because the plane couldn’t fly that far. 36S to 39.5S is ruled out because it’s been searched. 34S to 36S is ruled out for the reasons discussed above. And north of 34S is ruled out because the debris would have been spotted during the surface search.

This is where we stand, three years after the disappearance: with lots of different kinds of clues delimiting where the plane could have gone, it’s hard to make a plausible case that MH370 went anywhere.

UPDATE: Elle Hunt has written a story in the Guardian about Victor’s criticism of the ATSB’s new search zone. Unfortunately it takes seriously the idea that 30S is a plausible alternative. In addition to the ATSB’s assertion that the debris here would have been spotted during the surface search phase, there are the additional problems that:

• Low-windage debris would have reached the coast of southern Africa in early 2015, and the flaperon would have arrived in Réunion late 2014. Both are way too early.
• This endpoint was calculated as having a zero percent probability in the DSTG Bayesian analysis of the Inmarsat data.

The Australian Transport Safety Board (ATSB), the organization overseeing the now-suspended ocean search for MH370, has just released a meaty drift-modeling report put together by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), a scientific research arm of the Australian government, entitled “The search for MH370 and ocean surface drift – Part II.” It provides a fascinating level of detail into the research previously detailed by the CSIRO. Most media write-ups of the report emphasize the CSIRO’s own top-line assessment of the work’s significance, namely that “The only thing that our recent work changes is our confidence in the accuracy of the estimated location, which is within the new search area identified and recommended by the First Principles Review.” However, I think it would be more accurate to say that this newly detailed view of the CSIRO’s research points up what a baffling picture the combined evidence presents. To wit:

FLOAT TESTS. Previously, the ATSB had released details of float tests involving replica flaperons. It turns out that these in fact did not float very much like the flaperon retrieved from Réunion and tested in a flotation tank in France. To obtain better data, the CSIRO scientists obtained an actual 777 flaperon and cut it down to the exact (within 2 cm) shape of the real flaperon. (Neat video here shows exactly what part of the trailing edge came away; pity that no analysis has been done to explain what kind of impact might have produced this result.) The cut-down flaperon turned out to float very much like the original, unlike the replicas, as you can see in the image above.

This cut-down flaperon was put out to sea and its drifting characteristics measured. This data was then entered into CSIRO’s drift models. It turned out that the trajectories starting from the previously identified high-probability search area near 35 degrees south were now more likely to impact Réunion Island. Thus, CSIRO scientists were heartened that their previous conclusions were reinforced.

However, I see some other interesting aspects of this work that have not received much attention. For instance, check out these photographs of the cut-down flaperon’s trailing edges:

Hello! The majority of the trailing edge is above the waterline, regardless of the flaperon’s orientation. We already knew this, based on images of the French flotation tests, but the new view is clearer than ever. This is simply impossible to reconcile with the heavy incrustation of the Réunion flaperon’s trailing edge. Previously released videos have suggested that in windy conditions, this part of the flaperon could be periodically immersed, but videos attached to the new report show that in light wind they will stay high and dry for extended periods. Lepas barnacles cannot survive and grow under these conditions.

Intriguingly, the report mentions that four replica flaperons that had been outfitted with telemetry were allowed to float in the open sea for an extended amount of time, but no mention was made of what biofouling they experienced. I would be very curious to know.

DRIFT MODELING. Using the new flaperon drift data, CSIRO asked: presuming an entry point at any given location along the seventh arc, how long would it take a piece of debris to reach Réunion, the coast of Africa, and the coast of Australia? Their results are shown below.

The red-and-white vertical line in the central image shows the arrival time at Réunion. It appears that this is roughly consistent with a start point anywhere between 30S and 40S. Further north, and it would have arrived earlier; further south, and it wouldn’t have gotten there at all. So that’s all good.

Note, however, that debris starting in that range should have arrived in Africa even earlier. In fact, debris only started turning up about five months later. So that’s a bit of a puzzle.

Note also that debris entering the water at south of about 36S should have washed up in Western Australia. Intriguingly, debris that entered around 34S should have also hit Australia. Thus, it seems to CSIRO that there is a fairly narrow window of entry points around 35S that is consistent with both the presence of debris on Réunion and the absence of debris in Australia.

IMPACT OF SURFACE SEARCH. Confoundingly, the document also includes a graphic showing the estimated probability that debris from any given entry point would have been spotted during the extensive surface search conducted by ships and airplanes in the months immediately after the disappearance. This is a bit of a shocker: CSIRO asserts that if the plane impacted north of 33S, there is essentially a 100 percent chance it would have been spotted.

Taken together, these newly released bits of information explain why CSIRO feels reinforced confidence that the plane likely hit the water in a fairly narrow band near 35 degrees south. A problem, as the report acknowledges, is that this area has already been searched up to about 20 nautical miles inside and outside the 7th arc. Presuming that the plane was in a nearly vertical dive at the time of the 7th arc, it is hard to see how it is possible that it came to rest further than this.

The report’s executive summary suggests that it is physically possible that the aircraft could have reached some small distance beyond this:

The new search area, near 35°S, comprises thin strips either side of the previously-searched strip close to the 7th arc. If the aircraft is not found there, then the rest of the search area is still likely to contain the plane. The available evidence suggests that all other regions are unlikely.

I find it very interesting that the CSIRO is saying that, in essence, there is no other plausible end point that fits with the data in hand. The aircraft must be here, or else…

To my mind, the high-and-dry trailing edge of the flaperon suggests that “or else” should receive some decent consideration.

PS: A reasonable question to ask is: Why wasn’t this area searched? The short answer is that it was, but only partially. The area was within the initial search zone, such that “between latitudes 32.8°S and 36°S along the 7th arc the area has been searched to widths which vary from ~12 to 17 NM to the east and ~10 to 21 NM to the west of the 7th arc,” as reported in the First Principles Review.

Eventually the DSTG refined their analysis and concluded that a Bayesian analysis of possible flight paths suggested that an endpoint north of 35.5S was unlikely, so subsequent efforts were concentrated on an area south of 36S.

The First Principles Review also reports that ATSB investigators concluded that the wreckage could not reasonably lie more than 25 nautical miles from the 7th arc.

The distance from 34S to 36S is 350 kilometers. If we say that the area remaining to be searched inside the arc is 10 nm, or 18.5 km, wide, and that the area outside the arc is about the same, then the total area remaining to be searched is roughly 13,000 square kilometers, or about 1/10th of the area searched so far.

But, as I’ve written before, the ATSB realized this quite a while before they ran out of time and money for the seabed search, and they made no effort to look there (except a little bit at the very end).

I personally wonder how at downward-plunging plane could get even 10 nm from the 7th arc. But it’s worth bearing in mind that what the Inmarsat analyis tells us, and what the seabed search tells us, and what the drift analysis tells us, don’t get along very well with one another.