What was found
PRIOR TO DESCENT FROM FL370, THE RUDDER PEDAL AUTHORITY DEGRADED TO THE POINT OF REQUIRING SIGNIFICANT RUDDER PEDAL DISPLACEMENT TO YAW THE AIRCRAFT. THE RUDDER TRIM WOULD MOVE, BUT REQUIRED EXCESSIVE FORCE. THE CONDITIONS CONTINUED UNTIL PASSING 15,000 FT IN THE DESCENT. BOTH RUDDER AND TRIM RETURNED TO NORMAL AND RUDDER LIMITER OPERATES NORMAL. REMOVED AND REPLACED RUDDER POWER PACK IAW MD80 AMM 27-20-8-4. PERFORMED ADJ/TEST OF 27-20-8-4 STEPS 4A1-19, COMPLETED ADJ/TEST OF 27-20-8-4 STEPS 20 & 21. OPERATION OK AT THIS TIME.