This is a question and maybe a little bet of speculation I hope you don't mind me posting this here, and please feel free to correct me if you think I am wrong.
In 1972 Eastern Air Lines, Flight 401 crashed. The probable cause was: "The failure of the fight crew to monitor the flight instruments during the final 4 minutes of flight, and to detect an unexpected descent soon enough to prevent impact with the ground. Preoccupation with a malfunction of the nose landing gear position indicating system distracted the crew's attention from the instruments and allowed the descent to go unnoticed."
However in the final report,
http://libraryonline.erau.edu/online...s/AAR73-14.pdf the NTSB alluded to the possibility that the captain may have caused the autopilot to disconnect when the captain bumped his control column while turning around and ordering his co pilot down to look at the visual nose gear indicator, down a hatch in the cockpit. This only required 15 lbs, or 7.5 kg of force to deactivate the autopilot's pitch control. This might have been a spit second bump on the control column.
I am wondering if Boeing saw that report and decided that more assertive inputs were needed on the control column to kick the auto pilot off to prevent a similar accident from happening again? The NTSB made loads of recommendations, but nothing like that.