FLT CTL PROBS CLBING THROUGH FL260 IN AN MD11.

Narrative

I WAS HAND FLYING THE ACFT TO CRUISE ALT (FL390) THROUGH FL260; AND THE AIRPLANE STARTED PITCH OSCILLATIONS ON ITS OWN. I RELEASED THE YOKE TO SEE IF THE OSCILLATIONS WOULD DAMPEN; BUT THEY CONTINUED TO INCREASE IN MAGNITUDE. THE ELEVATOR WAS BEING COMMANDED ON ITS OWN. I TOLD THE CAPT OF THE PROB; AND HE TOOK CTL OF THE ACFT. THE OSCILLATIONS CONTINUED. WE ENGAGED THE AUTOPLT TO SEE IF THAT HELPED THE SIT. THE OSCILLATIONS SEEMED TO CEASE. THERE WAS NO INDICATION ON THE SYNOPTIC DISPLAY OF FLT CTL MOVEMENT. THE AUTOPLT WAS THEN DISENGAGED; AND THE OSCILLATIONS RESUMED. WE RE-ENGAGED THE AUTOPLT; DECLARED AN EMER; AND REQUESTED TO RETURN TO EWR. THE CAPT DSNDED WITH THE AUTOPLT ON; SLOWED; LIMITED THE BANK ANGLE; USED A SHALLOW RATE OF DSCNT SO AS NOT TO UPSET THE DELICATE CTL OF THE AIRPLANE AND MAKE ANY SUDDEN CTL INPUTS. WE CHKED THE EMER PROCS; AND THERE WAS NO CHKLIST TO ADDRESS THE SIT. WE USED THE 'STABILIZER INOP' CHKLIST AS A GUIDELINE AND ELECTED TO ADD 20 KTS TO V-APCH. THE CAPT HAD EVERYTHING TRIMMED UP AND STABILIZED; DISCONNECTED THE AUTOPLT AT 1000 FT AND MADE AN UNEVENTFUL LNDG. CRM WAS EXCELLENT. ATC WAS EXTREMELY HELPFUL ONCE WE DECLARED AN EMER. IN HINDSIGHT; THERE ARE PLENTY OF INSIGHTS THAT MIGHT HAVE HELPED US IDENT A PROB EARLIER; IE; THE L ELEVATOR LAGGED ON THE PREFLT CHK; 3 PREVIOUS WRITE-UPS ON THE ELEVATOR AND PITCH AND AUTOPLT. EXCESSIVE TRIM WAS REQUIRED DURING CLBOUT. LOSS OF PITCH CTL IS A VERY SERIOUS PROB AND WE FELT IT WAS MOST IMPORTANT TO GET THE AIRPLANE ON THE GND SAFELY AND EXPEDITIOUSLY WHEN WE DID. THERE'S PROBABLY NOTHING WE WOULD HAVE DONE DIFFERENTLY IN THE SIT. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING INFO: THERE HAD BEEN A PREVIOUS MAINT LOG ITEM FOR A SIMILAR PROB. MAINT HISTORY SHOWED #1 FLT CTL COMPUTER WAS REPLACED; AND THE JACKSCREW/CHAINS AND ACTUATORS WERE VISUALLY INSPECTED AND FUNCTIONALLY TESTED. THEY CHKED OK. ELECTRICAL CONNECTORS ON THE L INBOARD ACTUATOR WERE REPLACED DUE TO MOISTURE. THE R OUTBOARD ELEVATOR ACTUATOR SHUTOFF SOLENOID WAS REPLACED FOLLOWED BY AN UNSUCCESSFUL TEST FLT. THE L INBOARD ELEVATOR SOLENOID SHUTOFF VALVE WAS REPLACED FOR A SUCCESSFUL REPAIR OF THE PROB. THE MEMORY OF THE FLT CTL COMPUTERS WAS ANALYZED AND MAINT ENGINEERING BELIEVES THAT THE REACTION OF THE ACFT WAS CONSISTENT WITH THE SOLENOID FAILURE.