@Gysbreght
You state that as a fact, but on what basis?
Sure, the plane must have turned south at some time between 18:29 and 19:41, but when?
I've spent a lot of time on this point, I was originally of the opinion that the plane went further west before making the turn.
But after working with the ping rings and taking into account fuel burn limitations I have come to the conclusion that even as far as IGOGU is extremely unlikely. Also there would have been no reason to have gone that far, the normal airline routes past the northern tip of Indonesian Territory are through IGEBO, so I conclude that's about where the turn was made.
This would have occurred
about 18:47.
If you have other theories, I'd like to hear them.