I have looked at the potential ping modelling techniques in previous posts, and also the recently released INMARSAT Doppler data/model which I think I have understood.
The new AMSA map shows the aircraft speed to the new search area as 400kt, down from 472kt (average). A couples of points follow:
1. The new search area is directly on the published last ping arc so it is being assumed that the aircraft crashed directly after the last ping, the new range being only just enough to get to the arc.
2. If (if) the interim ping signals had been used, this constrains the heading and speed quite closely, if a Great Circle route is assumed. Capt Kremin proposed the constant magnetic heading idea some days ago which causes the aircraft to turn to the East late in the track. As I stated at the time, this would remain consistent with the ping data for a GC route, but reduces the modelled speed. The diagram I generated at the time is below, the yellow line is the constant magnetic heading, the red line the last ping arc. The penultimate point on the grey GC route (on the final ping arc) was chosen to roughly match the original search area – of course the interim ping signals/arcs have not been released.
3. Changing the assumed speed would cause problems for the Doppler model that INMARSAT used. This is very sensitive to the aircraft speed which has to be removed to reveal the spacecraft Doppler signal used to decide it was on the Southern route.
If (if) the interim ping arcs are being used and are still constraining the choice of route and hence search area, I would guess that the constant magnetic heading option is now being used, which allows a shorter required range.
I don’t know what the INMARSAT Doppler model will have to do to match the new modelled speed.
Yellow line is the constant magnetic heading, grey line the GC route with matching modelled ping arcs, the red line the published last ping arc.