Narrative:

We were cleared from FL190 to 10000 ft. The autoplt was engaged. Descending through 11000 ft; we were given clearance to a heading to intercept the localizer runway 23R. The altitude capture annunciated on the HSI and I proceeded to extend the centerline and arm the localizer. When I looked up again; the aircraft was passing through 10000 ft at a rate of 1500 FPM. I disconnected the autoplt and corrected back to altitude. After I had disconnected the autoplt; the elevator appeared to take an unusual amount of pressure to move. By the time the aircraft stopped descending; we were at least 400 ft below 10000 ft. Later; on approach while hand flying; I asked the captain 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 maintenance accordingly. The 2 previous flts had written up similar anomalies; but maintenance attributed it to the center autoplt; and they placarded it. We were using the right autoplt at the time. Callback conversation with reporter revealed the following information: reporter advised they were in descent in the flight level change 'flch' mode and that the altitude capture annunciator illuminated. The autothrottles were engaged but failed to move forward; likely due to the fact the descent was not arrested and; therefore; speed was controled by elevator inputs rather than throttles. He added that they made a subsequent 'test' leveloff at a lower cleared altitude 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 captain speculated the possibility of ice buildup somewhere in the system was the cause. Maintenance indicated the earlier write-ups on the center autoplt were attributable to 'servo drag.' the center autoplt was deferred as a result.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.