What was found
(CAN) DURING DESCENT, AIRSPEED DECREASED TO 280 KNOTS, AUTO PILOT OUT OF TRIM LIGHT ILLUMINATED. AIRCRAFT LEVELED OUT AT 11,000 FEET AND AIRSPEED REDUCED TO 250 KNOTS, LIGHT REMAINED ON. AUTO PILOT #1 DISENGAGED AND AIRCRAFT NOTICEABLY NOSE HEAVY. ALL TRIMS TRIED, UNABLE TO MOVE HORIZONTAL STAB. MAINTENANCE ACTION INVOLVED CHANGING STAB DRIVE UNIT AND CHAIN. IT APPEARS THAT THE FUSE PIN IN THE DRIVE UNIT HAD FAILED.