P2J,
I understand from one source that the MD11 Smoke of Unknown Origin checklist by shutting down airflow to the cabin (aft of the fire source) actually reversed the airflow so that the smoke and fire progressed forward, to the cockpit. Perhaps some MD11 crews here can comment on this.
This was indeed one of the theories. It had to do with an air conditioning tube which was sealed with a silicon cap which melted when the fire started, then sucked the fire and smoke towards the recirculation fans in the cabin. This is why they believe the crew first saw something, but were not sure what, and the smoke then dissipated but they decided to land anyhow. The theory sais that moments after the cabin bus was shut down, the real serious problems began, so they link shutting down the cabin bus and the recirculation fans with it to the propagation of the fire within the aft bulkhead and the overhead area, causing a breakdown in the electrical system and eventually loss of all instruments.
This would explain a lot. If I remember right, the cabin bus was shut down as a part of the smoke of unknown origins checklist just before or during the turn to HDG 180 to dump fuel. From then on, things went out of control VERY fast.
Needless to say, the crew had absolutely NO WAY of knowing what was going on....
I think this theory was propagated in an excellent tv documentation about the crash, some coproduction of Swiss and Canadian TV. In my view one of the better documentaries of that accident.
Best regards
AN2 Driver.