Narrative:

Flight was from rdu to pit, preflight at rdu was normal, all systems checked good. Takeoff was accomplished and autoplt was engaged at 5000' MSL. Autoplt #2 was engaged. All airspeed, altitudes, and headings were input via either autoplt control panel or flight management computer (FMC). Flight was uneventful, and systems worked satisfactorily. Descent into pit was via inputs to FMC or acp. Aircraft intercepted localizer 28R pit as cleared by ATC. All status/ progress annunciations to pfd (primary flight display) indicated normal system operations. At approximately 1250' AGL autoplt #1 ganged with autoplt #2 as required for autoland and a 'land 2' annunciation appeared indicating autoland capability. Aircraft tracked ILS normally. At 150' RA I disengaged autoplt with control wheel disconnect switches. An aural calvary charge, and 2 sep annunciations indicated the autoplts had disconnected. Aircraft flew down and I began the round out for flare I noticed rudder movement. At first I thought that the captain was assisting on the rudders but as I touched down the rudder movement continued. At this time I realized the autoplt was still commanding rudder movement in an attempt to maintain runway centerline. No 'align' or 'flare' or 'row out' annunciations were displayed on either pfd to indicate autoplt was still engaged. I attempted to disconnect the autoplt using the autoplt disconnect bar on the glareshield. But this 'fool proof hard' disconnect did not work either. As we cleared the runway rudders continued to move in an attempt to regain localizer/runway centerline. I later found out that the rudder servo had an ice accumulation internally when prevented the servo from disconnecting. This is the second servo (1 rudder mine and 1 elevator servo) that has frozen in position. Keep an eye on this type aircraft guys'. Callback conversation with reporter revealed the following information. Aircraft was grounded after the incident for further check. Maintenance found rudder servo vent hole was in the 1200 O'clock position versus the 0600 O'clock. Correction was made to the fleet, completed in 1/91, and to this date have had no further problems. The rudder servo is identical to the unit used on the original non stretched version with the vent hole added. The aircraft is capable of automatic land and the flight crew is authority/authorized to make automatic land but the company uses CAT I minimums. The autoplt disconnect warning was normal even though the rudder servo was still connected. Apparently the disconnect senses only two servos, elevator and aileron. Reporter confirmed all indications of disconnect of the autoplt were normal.

Related reports:

Google
 

Original NASA ASRS Text

Title: FLT CREW OF MLG MADE AUTOLAND APCH AT 150 AGL DISCONNECTED AUTOPLTS BUT ONFLARE, TOUCHDOWN, TAXI, PLT FLYING FELT RUDDER MOVEMENT CAUSED BY AUTOPLT RUDDER CONTROL NOT DISCONNECTING AND ATTEMPTING TO STEER ACFT TO RWY CENTERLINE.

Narrative: FLT WAS FROM RDU TO PIT, PREFLT AT RDU WAS NORMAL, ALL SYSTEMS CHKED GOOD. TKOF WAS ACCOMPLISHED AND AUTOPLT WAS ENGAGED AT 5000' MSL. AUTOPLT #2 WAS ENGAGED. ALL AIRSPD, ALTS, AND HDGS WERE INPUT VIA EITHER AUTOPLT CTL PANEL OR FLT MGMNT COMPUTER (FMC). FLT WAS UNEVENTFUL, AND SYSTEMS WORKED SATISFACTORILY. DSNT INTO PIT WAS VIA INPUTS TO FMC OR ACP. ACFT INTERCEPTED LOC 28R PIT AS CLRED BY ATC. ALL STATUS/ PROGRESS ANNUNCIATIONS TO PFD (PRIMARY FLT DISPLAY) INDICATED NORMAL SYSTEM OPS. AT APPROX 1250' AGL AUTOPLT #1 GANGED WITH AUTOPLT #2 AS REQUIRED FOR AUTOLAND AND A 'LAND 2' ANNUNCIATION APPEARED INDICATING AUTOLAND CAPABILITY. ACFT TRACKED ILS NORMALLY. AT 150' RA I DISENGAGED AUTOPLT WITH CTL WHEEL DISCONNECT SWITCHES. AN AURAL CALVARY CHARGE, AND 2 SEP ANNUNCIATIONS INDICATED THE AUTOPLTS HAD DISCONNECTED. ACFT FLEW DOWN AND I BEGAN THE ROUND OUT FOR FLARE I NOTICED RUDDER MOVEMENT. AT FIRST I THOUGHT THAT THE CAPT WAS ASSISTING ON THE RUDDERS BUT AS I TOUCHED DOWN THE RUDDER MOVEMENT CONTINUED. AT THIS TIME I REALIZED THE AUTOPLT WAS STILL COMMANDING RUDDER MOVEMENT IN AN ATTEMPT TO MAINTAIN RWY CTRLINE. NO 'ALIGN' OR 'FLARE' OR 'ROW OUT' ANNUNCIATIONS WERE DISPLAYED ON EITHER PFD TO INDICATE AUTOPLT WAS STILL ENGAGED. I ATTEMPTED TO DISCONNECT THE AUTOPLT USING THE AUTOPLT DISCONNECT BAR ON THE GLARESHIELD. BUT THIS 'FOOL PROOF HARD' DISCONNECT DID NOT WORK EITHER. AS WE CLRED THE RWY RUDDERS CONTINUED TO MOVE IN AN ATTEMPT TO REGAIN LOC/RWY CTRLINE. I LATER FOUND OUT THAT THE RUDDER SERVO HAD AN ICE ACCUMULATION INTERNALLY WHEN PREVENTED THE SERVO FROM DISCONNECTING. THIS IS THE SEC SERVO (1 RUDDER MINE AND 1 ELEVATOR SERVO) THAT HAS FROZEN IN POS. KEEP AN EYE ON THIS TYPE ACFT GUYS'. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. ACFT WAS GNDED AFTER THE INCIDENT FOR FURTHER CHK. MAINT FOUND RUDDER SERVO VENT HOLE WAS IN THE 1200 O'CLOCK POS VERSUS THE 0600 O'CLOCK. CORRECTION WAS MADE TO THE FLEET, COMPLETED IN 1/91, AND TO THIS DATE HAVE HAD NO FURTHER PROBS. THE RUDDER SERVO IS IDENTICAL TO THE UNIT USED ON THE ORIGINAL NON STRETCHED VERSION WITH THE VENT HOLE ADDED. THE ACFT IS CAPABLE OF AUTO LAND AND THE FLT CREW IS AUTH TO MAKE AUTO LAND BUT THE COMPANY USES CAT I MINIMUMS. THE AUTOPLT DISCONNECT WARNING WAS NORMAL EVEN THOUGH THE RUDDER SERVO WAS STILL CONNECTED. APPARENTLY THE DISCONNECT SENSES ONLY TWO SERVOS, ELEVATOR AND AILERON. RPTR CONFIRMED ALL INDICATIONS OF DISCONNECT OF THE AUTOPLT WERE NORMAL.

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.