Sure the announcement, such as it is, doesnt tell anyone anything they didnt already know. I dont think it is that definitive as yet - I saw a screen grab of the text message that said "we can only assume..........".
Maybe they have definite proof but dunno why they wouldnt come out and say it if they have it.
I would say the evidence is fairly conclusive. However it's complicated and the media "doesn't
do complicated", which is why you probably haven't seen it reported. It comes from the Inmarsat satellite that picked up the signals (so-called "pings") from the plane's ACARS system. Although the pings contained no data (because the ACARS data was seemingly intentionally switched off in the first half hour of flight), the following was able to be ascertained up until last week:
- the last transmitted ping was seven and half hours after the plane took off from Kuala Lumpur;
- the plane was travelling during that time -- this is known from the timing of the pings, which showed the transmitter was carrying them away from the receiving satellite which is stationary over the equator;
- it wasn't known which of two directions the plane was travelling, hence the attention on alternate northern and southern corridors that the plane could have travelled;
The latest information is based on a new analysis of the pings which relies on the well-known Doppler effect, the same technique that a traffic cop's radar gun uses to detect the speed of a moving car. Radio signals move up and down in frequency depending on whether the object is moving toward or away from the receiver. The Inmarsat equipment wouldn't normally be used in this way, in fact this technique has never been used before, hence the reason why it has taken this long to obtain. (Frankly, I'm surprised that they even record the raw signal in a form that would allow this to be done, but it seems they do).
This was also probably not a simple job -- the signal is probably frequency or phase modulated, which means there is inherent movement in the received frequency even from a stationary transmitter. Also, the satellite is over 22 thousand miles above the equator and the plane is only travelling a very short distance horizontally over the surface of the earth during a single ping transmission, which means that the change in the plane's distance from the satellite (on which the Doppler calculation relies) is very small. So, even though the cumulative time delay builds up to give the previously known information about the overall flight path (north or south), the directional information from a single ping must be nearly non-existent. Furthermore -- and this is an aspect I don't think has been reported on yet -- the Doppler shift magnitude is not itself direction sensitive. So they presumably used either: 1) the fact that the plane started north of the equator (Kuala Lumpur is at 3° N) and approached the satellite before travelling away again, indicating a north-south trajectory, or 2) the satellite's own small daily drift north and south of the equator was used. They say they will give more details at press briefings tomorrow (Malaysian ministry of transport press conference, afternoon local time on 25th).
I gather that they used historical data from hundreds of flights to look at the signal patterns and compare them to MH370. This would have been a very complicated modelling job and statistical analysis. The Inmarsat results would probably have included a confidence level but I haven't seen that reported. However, in the end they consider the results unambiguous, and Inmarsat had them peer reviewed before releasing them to the Malaysian government. There seems to be little doubt now that the plane flew along the southern track and ended up in the Indian Ocean. The best that can be hoped for now is that debris is positively identified in time to backtrack to a likely crash location -- a calculation fraught with its own difficulties due to chaotic currents in the southern ocean -- while the flight data recorder and cockpit voice recorder sonar beacons are still operational.