Narrative:

Approaching ZZZ from the south, setting up for approach and landing to runway 8R. Experienced right FMC failure while coupled to right autoplt. Received autoplt disconnect and autothrottle disengage warnings and alert sounds. However, noted unable to get a clean disconnect from right autoplt couple. First officer on alternate FMC married data ranges for first officer HSI course information off left FMC. Used raw data for runway 8R ILS DME. Procedures good. However, autoplt anomaly complicated event. Unable to cleanly disconnect right autoplt. Used gang bar to effect complete autoplt disconnect. After reseating autoplt disconnect gang bar, unable to couple up to any autoplt including left autoplt. Notified approach control of loss of right FMC. Approach notified heads up, pay more attention to our flight. Approach cleared us to turn in to intercept course into runway 8R and descend to 1500 ft MSL. We experienced more autoplt disconnect problems. Notified approach of desire not to turn to intercept course but to extend final to work with aircraft to clean up autoplt malfunction to clean up warnings/cautions and make sure autoplts were cleanly uncoupled from aircraft flight operation. We had begun our descent when approach stated, not knowing we would have more in-flight problems, 'you don't have to climb back to 3000 ft, but try to level off for me now at 2500 ft until you can accept your course intercept runway 8R clearance.' we acknowledged. Aircraft with autoplts disengaged pitched up as first officer was flying. First officer applied forward pressure on control to stop climb at about 2670 ft MSL. I utilized the autoplt disengage gang bar once again and aircraft for first time during this entire sequence of events felt free of any autoplt input. Additionally, during this event, the autoplt disengage buttons on both control columns appeared inoperative. Neither button disengaged or effected normal cessation of alerts. Aircraft flight operation with system failures as noted handled normally from this point on throughout landing and taxi clear of runway. At the gate, entered all pertinent data regarding right FMC failure and autoplt anomaly in logbook. Callback conversation with reporter revealed the following information: the reporter stated the yoke switches, paddles and gang bar all failed to disconnect the right autoplt. The reporter said the first officer had to fight the control inputs from the failed autoplt until a disconnect was obtained by holding the gang bar for a slight interval. The reporter stated the company maintenance will offer no information on the cause of this incident.

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Original NASA ASRS Text

Title: A B757-200 ON APCH AT 3000 FT EXPERIENCED FAILURE OF THE R FMC. FOUND AUTOPLT WOULD NOT DISCONNECT AND CONTINUED INPUTS TO CTLS.

Narrative: APCHING ZZZ FROM THE S, SETTING UP FOR APCH AND LNDG TO RWY 8R. EXPERIENCED R FMC FAILURE WHILE COUPLED TO R AUTOPLT. RECEIVED AUTOPLT DISCONNECT AND AUTOTHROTTLE DISENGAGE WARNINGS AND ALERT SOUNDS. HOWEVER, NOTED UNABLE TO GET A CLEAN DISCONNECT FROM R AUTOPLT COUPLE. FO ON ALTERNATE FMC MARRIED DATA RANGES FOR FO HSI COURSE INFO OFF L FMC. USED RAW DATA FOR RWY 8R ILS DME. PROCS GOOD. HOWEVER, AUTOPLT ANOMALY COMPLICATED EVENT. UNABLE TO CLEANLY DISCONNECT R AUTOPLT. USED GANG BAR TO EFFECT COMPLETE AUTOPLT DISCONNECT. AFTER RESEATING AUTOPLT DISCONNECT GANG BAR, UNABLE TO COUPLE UP TO ANY AUTOPLT INCLUDING L AUTOPLT. NOTIFIED APCH CTL OF LOSS OF R FMC. APCH NOTIFIED HEADS UP, PAY MORE ATTN TO OUR FLT. APCH CLRED US TO TURN IN TO INTERCEPT COURSE INTO RWY 8R AND DSND TO 1500 FT MSL. WE EXPERIENCED MORE AUTOPLT DISCONNECT PROBS. NOTIFIED APCH OF DESIRE NOT TO TURN TO INTERCEPT COURSE BUT TO EXTEND FINAL TO WORK WITH ACFT TO CLEAN UP AUTOPLT MALFUNCTION TO CLEAN UP WARNINGS/CAUTIONS AND MAKE SURE AUTOPLTS WERE CLEANLY UNCOUPLED FROM ACFT FLT OP. WE HAD BEGUN OUR DSCNT WHEN APCH STATED, NOT KNOWING WE WOULD HAVE MORE INFLT PROBS, 'YOU DON'T HAVE TO CLB BACK TO 3000 FT, BUT TRY TO LEVEL OFF FOR ME NOW AT 2500 FT UNTIL YOU CAN ACCEPT YOUR COURSE INTERCEPT RWY 8R CLRNC.' WE ACKNOWLEDGED. ACFT WITH AUTOPLTS DISENGAGED PITCHED UP AS FO WAS FLYING. FO APPLIED FORWARD PRESSURE ON CTL TO STOP CLB AT ABOUT 2670 FT MSL. I UTILIZED THE AUTOPLT DISENGAGE GANG BAR ONCE AGAIN AND ACFT FOR FIRST TIME DURING THIS ENTIRE SEQUENCE OF EVENTS FELT FREE OF ANY AUTOPLT INPUT. ADDITIONALLY, DURING THIS EVENT, THE AUTOPLT DISENGAGE BUTTONS ON BOTH CTL COLUMNS APPEARED INOP. NEITHER BUTTON DISENGAGED OR EFFECTED NORMAL CESSATION OF ALERTS. ACFT FLT OP WITH SYS FAILURES AS NOTED HANDLED NORMALLY FROM THIS POINT ON THROUGHOUT LNDG AND TAXI CLR OF RWY. AT THE GATE, ENTERED ALL PERTINENT DATA REGARDING R FMC FAILURE AND AUTOPLT ANOMALY IN LOGBOOK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE YOKE SWITCHES, PADDLES AND GANG BAR ALL FAILED TO DISCONNECT THE R AUTOPLT. THE RPTR SAID THE FO HAD TO FIGHT THE CTL INPUTS FROM THE FAILED AUTOPLT UNTIL A DISCONNECT WAS OBTAINED BY HOLDING THE GANG BAR FOR A SLIGHT INTERVAL. THE RPTR STATED THE COMPANY MAINT WILL OFFER NO INFO ON THE CAUSE OF THIS INCIDENT.

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.