Early Inmarsat route calculation, from Ashton et al.
A week after MH370 went missing, the Malaysian government dropped a shocker: Inmarsat, the satellite communications provider, had recorded signals from the plane that allowed them to calculate the plane’s distance from the satellite about once an hour for nearly six hours.
At first, the Malaysians only released a rough sketch of the final arc: two matching fragments of a circle, 3000 miles in radius, that stretched from Kazakhstan in the north to the remote Indian Ocean in the south. This in itself was a major step forward, in that it drastically reduced the numer of possible places the plane could have gone. But even more enticingly it suggested that if we had the numerical values for all the pings, and could figure out what speed the plane was flying at, we would be able to identify the route that the plane was taken and thus its precise final destination.
The scientists at Inmarsat recognized this immediately, and as Chris Ashton et al relate in their paper in the Journal of Navigation, they quickly plugged in the most logical speed value — typical airliner cruise speed, around Mach 0.83 — and concluded that the plane flew either to the middle of Kazakhstan or almost directly south into the Indian Ocean. (See image above.) As a result, the Malaysian government submitted a request to the Kazakh government asking that it be allowed to set up a search operation in the country, and planes were dispatched to search the ocean surface near the southern potential end point. Hopes were high. After satellites spotted what appeared to be floating material in the southern ocean, Australian Prime Minister Tony Abbott told his country’s parliament that it was a “potentially important development.’’
Of course the idea that the plane flew straight and fast, as airliners typically do, was just an assumption. Theoretically, it could have flown from ping ring to ping ring at any number of speeds along any number of routes, including straight, curvy, and zig-zag. Most of these alternatives would have resulted in the plane winding up at a lower latitude. And indeed, within a few days the authorities abandoned the southernmost search area and started scouring a section of the ocean much further north. The decision to shift the search zone appears to have been heavily influenced by a second set of data also derived from the handshakes exchanged between the plane and the satellite: the so-called BFO (“burst frequency offset”) data. After much head-scratching, Inmarsat believed that they had come up with an algorithm that allowed them to understand the physical implications of this data, and it told them that a) the plane had definitely gone south, not north, and b) the plane had not been flying straight and fast, as initially supposed, but instead taken a slower and/or meandering course and wound up about a thousand miles from the initial search area.
Frustratingly, for those of us who were watching from the sidelines and eager to understand what was going on, neither Inmarsat nor the Malaysians were willing to either release their numerical data nor to explain their BFO algorithm. We just had to take their word for it. Which was enormously frustrating, since it seemed tantalizingly plausible that if we had the data and understood the physical processes that generated it, we would be able to mathematically solve for the location of the plane. Et voila: mystery solved.
Finally, after much pressure from the public, the Malaysians did finally release most of the Inmarsat data in May; the following month, the Australian Transport Safety Bureau (ATSB) released a report which explained how the then-current search area had been arrived at and explained in some detail how the BFO algorithm worked.
Many independent experts, including members of the Independent Group, leapt at the chance to finally get under the hood of the BFO algorithm and see if they could reach their own conclusions about where the plane went. In time, however, their optimism faded. In turns out that the BFO data offers only a very imprecise gauge of a plane’s location or direction of travel. To test the algorithm, for instance, scientists working for the search effort compared BFO data received from a known flight with the plane’s actual path. They found that, of the thousands of possible paths that matched the BFO data, even the one that most closely matched the actual flight was hundreds of miles off in places.
We seemed to be almost back to where we started: we had a set of ping rings that showed us seven quite accurate (within 10 km, the ATSB estimates) arcs along which the plane must have been at seven moments in time, but with only vague intimations of where along those arcs the plane actually was.
Gradually, however, without much fanfare, it has become clear that other, non-BFO techniques can provide insight into how MH370 was traveling after it disappeared from radar, and these in turn offer a strong suggestion about where the plane went.
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