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.