OPERATING ON THE R AUTOPLT; B767-300ER FAILS TO CAPTURE PROGRAMMED ALT WHILE IN DSCNT. DURING RECOVERY AND SUBSEQUENT MANUAL FLT; ELEVATOR CTL RESISTS UP ELEVATOR INPUTS UNTIL RELEASING UNDER PRESSURE FROM BOTH PLTS.

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WE WERE CLRED FROM FL190 TO 10000 FT. THE AUTOPLT WAS ENGAGED. DSNDING THROUGH 11000 FT; WE WERE GIVEN CLRNC TO A HDG TO INTERCEPT THE LOC RWY 23R. THE ALT CAPTURE ANNUNCIATED ON THE HSI AND I PROCEEDED TO EXTEND THE CTRLINE AND ARM THE LOC. WHEN I LOOKED UP AGAIN; THE ACFT WAS PASSING THROUGH 10000 FT AT A RATE OF 1500 FPM. I DISCONNECTED THE AUTOPLT AND CORRECTED BACK TO ALT. AFTER I HAD DISCONNECTED THE AUTOPLT; THE ELEVATOR APPEARED TO TAKE AN UNUSUAL AMOUNT OF PRESSURE TO MOVE. BY THE TIME THE ACFT STOPPED DSNDING; WE WERE AT LEAST 400 FT BELOW 10000 FT. LATER; ON APCH WHILE HAND FLYING; I ASKED THE CAPT TO ASSIST ME ON THE BACK-PRESSURE OF THE ELEVATOR; BECAUSE IT APPEARED TO BE STICKING; AND IT SUDDENLY RELEASED. THERE APPEARED TO BE NO OTHER ELEVATOR ANOMALIES AFTER THAT; AND WE LANDED UNEVENTFULLY. WE ENTERED THE FAULT IN THE LOGBOOK AND DEBRIEFED MAINT ACCORDINGLY. THE 2 PREVIOUS FLTS HAD WRITTEN UP SIMILAR ANOMALIES; BUT MAINT ATTRIBUTED IT TO THE CTR AUTOPLT; AND THEY PLACARDED IT. WE WERE USING THE R AUTOPLT AT THE TIME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THEY WERE IN DSCNT IN THE FLT LEVEL CHANGE 'FLCH' MODE AND THAT THE ALT CAPTURE ANNUNCIATOR ILLUMINATED. THE AUTOTHROTTLES WERE ENGAGED BUT FAILED TO MOVE FORWARD; LIKELY DUE TO THE FACT THE DSCNT WAS NOT ARRESTED AND; THEREFORE; SPD WAS CTLED BY ELEVATOR INPUTS RATHER THAN THROTTLES. HE ADDED THAT THEY MADE A SUBSEQUENT 'TEST' LEVELOFF AT A LOWER CLRED ALT AND THE FAILURE TO CAPTURE REPEATED. HE EMPHASIZED HIS CONCERN ABOUT THE 'STICKINESS' OF THE ELEVATOR UNTIL IT FELT AS THOUGH A RESTR WAS OVERCOME. BECAUSE THE ELEVATOR OPERATED NORMALLY SUBSEQUENT TO THE ONE INCIDENT; HE AND THE CAPT SPECULATED THE POSSIBILITY OF ICE BUILDUP SOMEWHERE IN THE SYS WAS THE CAUSE. MAINT INDICATED THE EARLIER WRITE-UPS ON THE CTR AUTOPLT WERE ATTRIBUTABLE TO 'SERVO DRAG.' THE CTR AUTOPLT WAS DEFERRED AS A RESULT.