[laken]

Yes, but this is where it gets a little complicated, and why this accident is so fascinating to many people in aviation...

>> if the nose of a plane suddenly drops, isn't the pilot's first instinct to pull back on the controls to raise it?

Not exactly, as the correct way to get out of a stall is pointing the nose down, in order to pick up airspeed to gain more lift. The stall horns were going off, so the pilots may have thought they were stalling. In addition, as others have mentioned, the yoke alone may be unable to beat out the trim by the autopilot.

>> From what I've read, in Boeing aircraft at least, the pilot's controls can always override the automatic systems.

Historically, you are exactly right. This is the _biggest_ reason pilots are pissed at Boeing right now. It's believed that the autopilot was turned off entirely when the plane started thinking it was stalling, and trying to point itself down. This is not present on any of the original 737 aircraft, only the MAX series, and Boeing didn't inform pilots of this.