The lack of a radio call is not relevant. 8 minutes may be a long time if you are doing nothing. When busy it can seem to last seconds. It is very low on the priority list.
The Lufthansa pitch down event last year was an activation of the angle of attack protection. It does NOT establish a stable dive, but would continue to push in forward stick. If kept up the dive would be vertical, not a stable 3,500 fpm descent. At the time it happened, there was no laid down procedure (there is now), but turning off two air data computers will force the aircraft into a flight law that does not have alpha protection. Once recognised, it would only take a few seconds. At this stage I don't see this as being a flight control event.
Interesting things. Stable heading. Reasonably stable sink rate. 3,500 fpm is not as extreme as being intimated by some. You don't hit it every day in normal ops, but easily attained if you want. To give you an idea, the 380 can probably hit 9,000 in a high speed descent with speed brake. QF30 descent was about 5,000 fpm.
