What was found
(CAN) ON ROTATION, F.O. REPORTED EXCESSSIVE BACK PRESSURE ON CONTROL COLUMN. HE THEN INPUT FULL FORWARD ELEVATOR TRIM TO COUNTERACT PITCH UP. ELEVATOR TRIMLOCKED IN FULL FORWARD POSITION AFTER INPUT. REQUIRED EXCESSIVE FORCE TO OVERCOME THE JAM. ON INITIAL INSPECTION, ICE BUILD-UP NOTED ON UPPER SURFACE WHICH WOULD CAUSE HEAVY ELEVATOR CONTROLS. MFG NOTED THAT IF EXCESSIVE FORCE WAS APPLIED IN THE FULL UP OR FULL DOWN POSITION OF THE SCREW JACKS, THEN INITIAL ADDITIONAL FORCE WOULD BE REQUIRED TO RETURN THE SCREW JACKS TOWARDS NEUTRAL. DEHAVILLAND HAS ISSUED AOM 481 TO COVER AND WILL BE TAKING FURTHER ACTION FOR THE OPERATING MANUAL AND INSPECTIONS.