[ventus45]

If we continue to trust the Isat data, at least the BTO's and the 7th Arc in general (but disregarding  the current understanding of the BFO's) we still have to accept the fact that it did not take a northern route, and did in fact go south to the SIO.

That said, everything post IGARI is up for discussion.  The Malaysian radar and the Malacca Strait information can not be accepted as fact, for too many reasons to list.

But, if we accept the Isat BTO's, then obviously the aircraft had to fly west, fast enough to reach the 18:25 / 18:40 arcs.

There are multiple ways the aircraft could have got from IGARI to the 18:25 / 18:40 arcs.  Performance limits for the aircraft set both northern and southern limits on those arcs.

The "accepted" theory, is within the "northern limit" and is:
Igari - Penang - Mekar and onwards north-west to the FMT.

I do not accept that theory for many reasons, as previously explained in this thread.

My theory is, pretty close to the "southern limit" and is:
Igari - Penang - Gotla - Medan VOR - Merim and onwards south-west towards Uprob, to a position 60 nautical miles short of Uprob.

The aircraft flew out of the radar coverage of the TNI's Sibolga PSR, and then, whilst maintaining heading towards Uprob (237.5 degrees true), initiated a fairly rapid descent to ensure dropping below the radar horizon.

Whilst on descent, passing FL300, it then commenced the FMT, to head south. The aircraft would have remained at or below FL300 probably until reaching the Equator, where it would have climbed to obtain optimum LRC conditions for onward cruise.



And here are the relevant times (for OceanKoto).