Narrative:

I was hand flying the aircraft to cruise altitude (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 captain of the problem, and he took control of the aircraft. The oscillations continued. We engaged the autoplt to see if that helped the situation. The oscillations seemed to cease. There was no indication on the synoptic display of flight control movement. The autoplt was then disengaged, and the oscillations resumed. We re-engaged the autoplt, declared an emergency, and requested to return to ewr. The captain descended with the autoplt on, slowed, limited the bank angle, used a shallow rate of descent so as not to upset the delicate control of the airplane and make any sudden control inputs. We checked the emergency procedures, and there was no checklist to address the situation. We used the 'stabilizer inoperative' checklist as a guideline and elected to add 20 KTS to v-apch. The captain had everything trimmed up and stabilized, disconnected the autoplt at 1000 ft and made an uneventful landing. CRM was excellent. ATC was extremely helpful once we declared an emergency. In hindsight, there are plenty of insights that might have helped us identify a problem earlier, ie, the left elevator lagged on the preflight check, 3 previous write-ups on the elevator and pitch and autoplt. Excessive trim was required during climb out. Loss of pitch control is a very serious problem and we felt it was most important to get the airplane on the ground safely and expeditiously when we did. There's probably nothing we would have done differently in the situation. Callback conversation with reporter revealed the following information: there had been a previous maintenance log item for a similar problem. Maintenance history showed #1 flight control computer was replaced, and the jackscrew/chains and actuators were visually inspected and functionally tested. They checked ok. Electrical connectors on the left inboard actuator were replaced due to moisture. The right outboard elevator actuator shutoff solenoid was replaced followed by an unsuccessful test flight. The left inboard elevator solenoid shutoff valve was replaced for a successful repair of the problem. The memory of the flight control computers was analyzed and maintenance engineering believes that the reaction of the aircraft was consistent with the solenoid failure.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 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.