Just an observation....but the 90' turn is the classic manoeuvre prior to commencing an Emergency Descent, i.e. to not descend through the Airway. If indeed the plane was suffering smoke in the cockpit and loss of significant instrument displays, compounded by it being the middle of the night, it is not too hard to envisage a poor outcome, especially with PNF struggling through a checklist in dire conditions and thus losing some of his monitoring ability. The big question of course remains , what triggered the problem in the first place and realistically, only the black boxes will tell us that answer if and when they are found.
Another sad loss.