Both the nose down input, by moving the control yoke forward, AND the trimming of the Hor Stab to 5 degrees nose down (simultaneously) could only have happened as a result of one or both pilots deliberately doing that. It couldn't have happened as a result of some "automatic" flight computer command. To me, that is an indication of an incompetent pilot (poorly, or not adequately trained).
Properly trained pilots would know that if you trim the Hor Stab to full nose down, that the plane will immediately go into a high speed dive, and unless there is a lot of altitude left, recovery will be impossible. That is because the elevators do not have enough remaining pitch control authority on their own, if the HS is trimmed to such an extreme nose down position. Thus, merely pulling back as hard as possible on the yoke, once the dive has commenced, will not pull the nose back up to any significant degree. Additionally, the HS CANNOT be trimmed back to a level, or slightly nose up flight position, so long as the pilots are pulling back as hard as they can on the yoke. That is because such action will stall the HS jack screws and they will not be able to trim the HS the other direction, until the pilots release their pressure on the yoke.
In other words, they have to stop pulling back on the yoke, before the HS will be able to trim back to a positive pitch angle. Well-trained pilots know this and they would never have allowed this kind of un-recoverable trim situation to develop in the first place. The fatal error was in trimming the HS so far to a nose down position. Once that happened, at an altitude of only about 3,000 ft., their fate was sealed.
Following the publication of an official preliminary report, it became clear the crash was caused by the incompetent actions of one or both pilots.
