OleOle
thanks for that work and the grasp it gives on the required error margin of the arcs. I would expect the great circle solution to turn to the right (west) when getting closer to the pole. Am i wrong or is the turn just too slight to see?
When going west over Malacca Strait in the first part of the track the a/c was heading always directly towards the satellite. Maybe from this part of the track inmarsat could put more constraints on speed.
Wind drift would also play a significant role.
The differences between a great circle and rhumb line are small for a track that is largely South and at these latitudes, and are hard to see at this scale. I looked at great circle, rhumb line and the constant magnetic bearing courses.
As you say, the final turning point to the Southly heading is not known and it might come out from analysis of the early ping data. Wind drift would be significant but would be the same for all tracks in roughly the same area so would not be a differentiator between the options, I think. Winds would be different on the possible North and South routes and could be one of the things that was used to rule out the Northly route.