Howard Hughes and others
I'm going to lift a couple of sections out of Capt Kremin's previous post here because it's evident that investigators will already know, based on the exact location of the previous six pings, whether the excursion south was likely to have been accidental or deliberate.
In the case of the "Ghost plane" scenario the aircraft, after it turned WNW would have been either tracking to a programmed FMC waypoint or it would have been in a lateral AP mode referenced on magnetic north, HDG or TRK, it does not really matter. If tracking to the FMC waypoint, once it reached it, it would have reverted to HDG.
For the aircraft to track direct to the area of the last known ping and the current search area, there are only two ways to do it. One is a programmed FMC waypoint and the other is someone flying the aircraft via the HDG or TRK button and taking into account the 30-35 degree change in magnetic variation encountered along the route.
His point is that the track revealed by the pings will show either a direct straight path, or one which curves due to reversionary AP modes and changes in magnetic variation. His post is complete with charts etc and is currently number 7541. Well worth reading.
A straight path would indicate a deliberate diversion. Since investigators are labelling the route deviation a deliberate diversion, it would be reasonable on this basis to rule out a ghost plane - and it doesn't really matter from which exact point the diversion south commenced, though his reasoning is based on the point 200nm WNW of Penang.