Bearfoil, one correction: I believe I was the one proposing the possible turn based on mm43's data. I didn't mean to impute something to mm43 he might not have said.
And my understanding is that once the speed indications differ the computers go off-line suddenly while the plane is likely in very heavy turbulence.
Something else came to mind. I'm not a pilot so this needs feedback from a real pilot. If something caused an engine stall, which could account for loss of ACARS transmissions, the pilots would not be concerned about compass heading so much as aligning the plane nose down to gain speed to restart the engines. This could have lead to the mysterious heading change. Then the desperate attempt to pull out as the ocean came into view might finish the scenario, engines started or not.
{^_^}