Narrative:

Aircraft system failure, flight controls. On short final IMC, aircraft was in approach mode. The autoplt pitched down 3 degrees and then pitched up about 4 or 6 degrees. I disconnected the autoplt and found the flight controls to be very stiff and erratic, even with the autoplt off. The only indication was a speed trim fail light. The aircraft was extremely difficult to control on the go around. Pitch and roll felt like manual reversion and/or the autoplt was still trying to put inputs to the control surfaces even while disconnected. As we gained altitude (difficult) and airspeed, during the clean-up the plane flew better. Went to a close holding pattern out of the WX to study a malfunction that is not in any of our procedures. As we configured a second time, problem occurred again. Flaps were retracted to the point where plane was more ctlable. We had to try combinations of autoplt on and off, and stabilizer on and off with manual trim to get the aircraft configured for another approach attempt. With autoplt off, we got it configured on the third attempt and shot a non ILS approach into ZZZZ. We had no indications of known flight control malfunctions that have occurred on the B737-800. We did land at ZZZZ in IMC at night with crash fire rescue equipment available. After many calls between maintenance controller and captain, our fleet supervisor, the aircraft was OTS. The level of interest made it to boeing. We then found out that a rather obscure maintenance service bulletin addresses what could have been the possible cause. Bottom line is this: we need to know what this plane can do to us. After a WX divert to ZZZZ1 and then fighting the WX again in ZZZZ, the absolute last thing a tired crew needs is a flight control malfunction that turns you into a test pilot in mountainous terrain at night. Callback conversation with reporter revealed the following information: reporter does not know what was found. Local contract maintenance did a computer bite check. Everything tested normal. The air carrier test pilots flew the aircraft. The aircraft has been released for service. The crew had conference calls with the FAA, the aircraft manufacturer, the chief pilot, flight supervisor, and air carrier engineering. The reporter describes it was like the aileron and elevator servos did not disengage. The crew turned off the master autoplt control on the glare shield. It did not help. At flaps 10 degrees, things were relatively normal. At flaps 15 departures, things bound up. The high speed stabilizer trim also was actuated. The crew turned off both high and low speed electric trim. They then used manual trim after that. The reporter was scheduled to have another conference call with the same parties, today.

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Original NASA ASRS Text

Title: B737-800 CREW HAD ELEVATOR AND CTL PROBS GOING INTO MGGT.

Narrative: ACFT SYS FAILURE, FLT CTLS. ON SHORT FINAL IMC, ACFT WAS IN APCH MODE. THE AUTOPLT PITCHED DOWN 3 DEGS AND THEN PITCHED UP ABOUT 4 OR 6 DEGS. I DISCONNECTED THE AUTOPLT AND FOUND THE FLT CTLS TO BE VERY STIFF AND ERRATIC, EVEN WITH THE AUTOPLT OFF. THE ONLY INDICATION WAS A SPD TRIM FAIL LIGHT. THE ACFT WAS EXTREMELY DIFFICULT TO CTL ON THE GAR. PITCH AND ROLL FELT LIKE MANUAL REVERSION AND/OR THE AUTOPLT WAS STILL TRYING TO PUT INPUTS TO THE CTL SURFACES EVEN WHILE DISCONNECTED. AS WE GAINED ALT (DIFFICULT) AND AIRSPD, DURING THE CLEAN-UP THE PLANE FLEW BETTER. WENT TO A CLOSE HOLDING PATTERN OUT OF THE WX TO STUDY A MALFUNCTION THAT IS NOT IN ANY OF OUR PROCS. AS WE CONFIGURED A SECOND TIME, PROB OCCURRED AGAIN. FLAPS WERE RETRACTED TO THE POINT WHERE PLANE WAS MORE CTLABLE. WE HAD TO TRY COMBINATIONS OF AUTOPLT ON AND OFF, AND STABILIZER ON AND OFF WITH MANUAL TRIM TO GET THE ACFT CONFIGURED FOR ANOTHER APCH ATTEMPT. WITH AUTOPLT OFF, WE GOT IT CONFIGURED ON THE THIRD ATTEMPT AND SHOT A NON ILS APCH INTO ZZZZ. WE HAD NO INDICATIONS OF KNOWN FLT CTL MALFUNCTIONS THAT HAVE OCCURRED ON THE B737-800. WE DID LAND AT ZZZZ IN IMC AT NIGHT WITH CFR AVAILABLE. AFTER MANY CALLS BTWN MAINT CTLR AND CAPT, OUR FLEET SUPVR, THE ACFT WAS OTS. THE LEVEL OF INTEREST MADE IT TO BOEING. WE THEN FOUND OUT THAT A RATHER OBSCURE MAINT SVC BULLETIN ADDRESSES WHAT COULD HAVE BEEN THE POSSIBLE CAUSE. BOTTOM LINE IS THIS: WE NEED TO KNOW WHAT THIS PLANE CAN DO TO US. AFTER A WX DIVERT TO ZZZZ1 AND THEN FIGHTING THE WX AGAIN IN ZZZZ, THE ABSOLUTE LAST THING A TIRED CREW NEEDS IS A FLT CTL MALFUNCTION THAT TURNS YOU INTO A TEST PLT IN MOUNTAINOUS TERRAIN AT NIGHT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR DOES NOT KNOW WHAT WAS FOUND. LCL CONTRACT MAINT DID A COMPUTER BITE CHK. EVERYTHING TESTED NORMAL. THE ACR TEST PLTS FLEW THE ACFT. THE ACFT HAS BEEN RELEASED FOR SVC. THE CREW HAD CONFERENCE CALLS WITH THE FAA, THE ACFT MANUFACTURER, THE CHIEF PLT, FLT SUPVR, AND ACR ENGINEERING. THE RPTR DESCRIBES IT WAS LIKE THE AILERON AND ELEVATOR SERVOS DID NOT DISENGAGE. THE CREW TURNED OFF THE MASTER AUTOPLT CTL ON THE GLARE SHIELD. IT DID NOT HELP. AT FLAPS 10 DEGS, THINGS WERE RELATIVELY NORMAL. AT FLAPS 15 DEPS, THINGS BOUND UP. THE HIGH SPD STABILIZER TRIM ALSO WAS ACTUATED. THE CREW TURNED OFF BOTH HIGH AND LOW SPD ELECTRIC TRIM. THEY THEN USED MANUAL TRIM AFTER THAT. THE RPTR WAS SCHEDULED TO HAVE ANOTHER CONFERENCE CALL WITH THE SAME PARTIES, TODAY.

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.