Tuesday, 25 March 2014

#MH370 : public and private understanding

 

Sitting in TV studio waiting rooms is a good way to meet and listen to experts with technical knowledge. Some days ago I had referred to the missing Malaysian airliner as posing us the ultimate IQ test. It now seems the test was solved in a few days, at least as regards probable location, if not probable motivation.

The Inmarsat story is a very interesting one, and is slowly being disclosed. As of this early morning the account was that there were 7 hourly “pings” to serve as the data points. Now it turns out that there was an 8th incomplete ping following shortly after the 7th, about 10 minutes later, and not at the usual hourly interval. This may have been an “exception report” coinciding with the moment of impact.

The early story was that, given these 7 hourly pings, Inmarsat was able to work out very quickly that they were consistent with transmissions coming from somewhere on an arc running North to South roughly from the point of the last radar contact with the plane. The presumption was that the satellite in geostationary orbit could calculate a possible arc from which the transmissions might have been sent, but no more than that. The increasing delays of transmission from plane to satellite might have been due to the plane travelling north or equally, south. How to resolve this directional issue?

Here is the Malaysian government’s explanation at to how Inmarsat did this:

In recent days Inmarsat developed an innovative technique which considers the velocity of the aircraft relative to the satellite. Depending on this relative movement, the frequency received and transmitted will differ from its normal value, in much the same way that the sound of a passing car changes as it approaches and passes by. This is called the Doppler effect. The Inmarsat technique analyses the difference between the frequency that the ground station expects to receive and that actually measured. This difference is the result of the Doppler effect and is known as the Burst Frequency Offset.

The Burst Frequency Offset changes depending on the location of the aircraft on an arc of possible positions, its direction of travel, and its speed. In order to establish confidence in its theory, Inmarsat checked its predictions using information obtained from six other B777 aircraft flying on the same day in various directions. There was good agreement.

While on the ground at Kuala Lumpur airport, and during the early stage of the flight, MH370 transmitted several messages. At this stage the location of the aircraft and the satellite were known, so it was possible to calculate system characteristics for the aircraft, satellite, and ground station.

During the flight the ground station logged the transmitted and received pulse frequencies at each handshake. Knowing the system characteristics and position of the satellite it was possible, considering aircraft performance, to determine where on each arc the calculated burst frequency offset fit best.

The analysis showed poor correlation with the Northern corridor, but good correlation with the Southern corridor, and depending on the ground speed of the aircraft it was then possible to estimate positions at 0011 UTC, at which the last complete handshake took place.

Burst frequency analysis is apparently well known, but to make offset calculations on Doppler like effects so as to infer location is an innovation. It would seem that when tested on real plane data these Doppler effect calculations matched the Southern arc better than the Northern arc. I still need to go through some further steps of understanding, but it seems very neat work, done very quickly. Once the most likely corridor of the flight path had been worked out, then calculations could be made on the fuel range of the aircraft so as to plot a likely impact location where both calculated ranges transected. Dropping sonar buoys in that area might pick up the last feeble transmissions from the black box. Finding debris will be another matter, and finding the wreck itself with the much prized black box even more problematical, and possibly not feasible.

Real time reporting of black box type data from aircraft is likely to be made mandatory, and eventually the black box will be as redundant as a library.

What these calculations show is that a minority can deal with probabilistic hypotheses based on statistical and scientific concepts, and usually those calculations are relatively private; and a majority would like to see publicly testable, absolutely tangible proofs, in the form of bodies and wreckage.

The private discussion has to be impersonal, detached, open to improvement and criticism, and rigorous when searching for errors. Reportedly, Inmarsat researchers eventually realised that a satellite in geostationary orbit is not in fact totally stationary, and by correcting for some drift were able to refine their location estimates. According to some accounts it was this correction which revealed the southern arc as the stronger hypothesis.

The grieving relatives want certainty, and want it in public. Scientists can only offer probability estimates, with the detailed results in private, or in that strange space, academic publication, where you have to know quite a bit about the subject in order to evaluate the paper, and can only discuss it with a few other people.

To cap it all, also not disclosed, quite properly, are the ways in which each airline deals with hijackers/terrorists. For example, it would not be good security to have it generally known how airlines intend to deal with hijackers, what distress codes they have put in place, how the cabin crew communicate with the pilots, and whether or not they can open the locked door to the cockpit, let alone why jets were not scrambled to shoot down the missing plane. Knowing this would aid public understanding. Keeping it private would assist security.

The Malaysian authorities released the wrong message. They announced certainty without even a shred of a wet paper napkin with the Malaysian Airways logo on it.  Private calculation understood by the few trumping the public bewilderment of the many.

They should have said something like: “The search continues for the plane and the passengers. All indications are that it came down in the far south of the Indian Ocean. It is very unlikely that there are any survivors. We are still searching for wreckage of the aircraft”.

All though it is unlikely now, one hopes that one day the relatives may rest in peace, free of the anxious torment of sweet dreams cruelly dashed.

 

4 comments:

  1. This comment has been removed by a blog administrator.

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  2. i'm atoning for that comment: pilot errors occur mainly during take-off & landing, mechanical errors are unlikely (unless they have bad mechanics) & routine maintenance logs exist. depending how high they were flying if the cabin became depressurized the plastic masks deliver only about 20 minutes worth of O2 to passengers (funny the flight attendants never mention that)! pilot O2 masks are better & last much longer:) the oceans are so full of debris that things found can be easily misidentified as belonging to this plane. so, the plot thickens.

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  3. I still don't understand how authorities find a different object everyday but yet it is no part of a plane...

    My questions are:
    - why did it take so long to deploy search teams?
    - Why no mayday from pilot?
    - How can we find a soccer ball in a middle of a soccer field using google map but we cant find a plane the size of a building?
    - Or the government knows something we don't?

    Check this video i found:
    https://www.youtube.com/watch?v=fj9pQN-Qxbo

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  4. Search teams took time to deploy because there was no agreed impact site, and still isn't. No mayday because the pilot did not chose to give one. We cannot find a soccer ball in the middle of a soccer field, not unless we specify the soccer field and the particular ball, which is not the task in this case. A plane is small in relation to an airport, and smaller in relation to an ocean. Very small. The government knows some things we do not know, but not much that is all that useful most of the time. Silly video.

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