This was a very tragic accident indeed. However, I am more than a little curious about one aspect of the event.
I flew the 747-400 for several years back in the 90’s. Ours were combi versions with the upper deck cargo area located behind a bulkhead which was located approximately even with the back of the wing.
If I remember correctly the pressurized airflow within the aircraft was from front to back, and vented overboard through 2 outflow valves located on the underside and at the rear of the airplane. In this configuration I would imagine that any cabin smoke or airborne contaminants would be drawn towards the rear and vented overboard.
Based on this, I am curious as to how the smoke intensity could become so great to advance forward and permeate into the enclosed upper deck cockpit so as the two pilots couldn’t see the instruments.
Am I missing something obvious here? Just wondering….