19960713025819A

(.4)The first officer (f/o) was making a descent from FL350 to FL240 in smooth air in VMC conditions with the autopilot (a/p) engaged. As the flight (flt) neared FL250, the captain became concerned that the airplane would not level off at FL240. He instructed the f/o to slow the rate of descent. The f/o attempted this by using the pitch thumbwheel on the a/p control panel. The captain then took control, attempted to overpower the a/p, and pulled back on the control yoke. With back pressure on the control yoke, he disengaged the a/p. with the reduced control column resistance after the a/p was disengaged, there was further excursion of the elevators to the up position. According to the flt data recorder, the airplane was subjected to a +2.28 g-load. A passenger in the aft lavatory suffered a fractured ankle. A 2nd passenger and 2 flt attendants received minor injuries. The MD-11 flight crew operating manual (fcom) advised against attempting to overpower the a/p; however, this was contained under the title, 'severe turbulence and/or heavy rain ingestion.' Each use of pitch thumbwheel interrupted the automatic level off, and the system would wait for 2 seconds after release of the thumbwheel before interrupted the automatic level off sequence again. Continued use of thumbwheel precluded the a/p from performing the level off at FL240. The manufacturer has issued fcom changes to warn pilots about the hazards of applying force to the control whell or column while the a/p is engaged and adjusting the pitch thumbwheel during a level off.