@DespairingTraveller
The aircraft being stationary, whether landed, crashed or ditched, is one possible interpretation, but so is that it remained flying, either along the arc for some reason, or on a course which intersected the arc in two places an hour apart, within whatever margin of error is implicit in the analysis. It could have ended its life flying round in circles, for example...
If we assume that it has not become stationary, but has continued to fly but has been present on the same arc at both 07:11 and 08:11, can we make the maths work if we know the changing direction of the southern arc if we follow it south and we assume that the aircraft is flying on a constant track? IE. Where would they have converged, as it were? Or would that not have occurred at all?