Narrative:

On approach to runway 18R dfw we were cleared to land. 1 aircraft had just landed and was on rollout. We observed another aircraft taking the runway. I asked my first officer to ask the tower about that aircraft. We were coming through about 5000 ft. After the first officer requested information on the aircraft, the tower told the traffic to expedite his takeoff. I observed the landing traffic still on the runway. I decided to take it around. I executed the go around. My first officer couldn't contact the tower right away due to other transmissions. During the go around, we were directed by the tower to a heading and frequency change. We went to 5000 ft as directed and 270 degrees. At 5000 ft I decided to engage #2 autoplt (#1 inoperative). The FMA showed heading select and altitude hold. Then I noticed the altitude was going about 100 ft low. I tried to correct by adjusting the vertical speed wheel. I could not move it. I disconnected the autoplt and flew the aircraft to 5000 ft. We got as low as 4700 ft. The vertical speed wheel was frozen at full down position to the gate. Information: #1 flight director was placarded inoperative. The captain side was bootstrapped to the copilot's. After takeoff from lax, I noticed that while hand-flying using the flight director, the vertical speed wheel was not working as well as it should, but when the #2 autoplt was engaged (#1 autoplt inoperative and placarded), the vertical speed wheel worked just fine. I wrote up the system going into dfw. After executing the go around at dfw, the tower asked if we needed assistance. I guess he didn't realize why I took it around. Supplemental information from acn 225482: with #1 autoplt engaged in altitude hold mode at 5000 ft MSL, the aircraft began a slow descent at which point the captain disconnected the autoplt and recaptured the assigned altitude. Maximum deviation was 300 ft. (There were several MEL'ed items associated with the FMS on this aircraft, but during this high workload situation we were unable to monitor the aircraft as desired.)

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Original NASA ASRS Text

Title: FLC EXECUTED GAR DUE TO PERCEIVED JUDGEMENT OF TFC SPACING OCCUPIED RWY. ACR X NON ADHERENCE TO ATC CLRNC DSCNT FROM OCCUPIED ALT DUE TO EQUIP PROBLEM AUTOPLT ALT HOLD. PLTDEV.

Narrative: ON APCH TO RWY 18R DFW WE WERE CLRED TO LAND. 1 ACFT HAD JUST LANDED AND WAS ON ROLLOUT. WE OBSERVED ANOTHER ACFT TAKING THE RWY. I ASKED MY FO TO ASK THE TWR ABOUT THAT ACFT. WE WERE COMING THROUGH ABOUT 5000 FT. AFTER THE FO REQUESTED INFO ON THE ACFT, THE TWR TOLD THE TFC TO EXPEDITE HIS TKOF. I OBSERVED THE LNDG TFC STILL ON THE RWY. I DECIDED TO TAKE IT AROUND. I EXECUTED THE GAR. MY FO COULDN'T CONTACT THE TWR RIGHT AWAY DUE TO OTHER TRANSMISSIONS. DURING THE GAR, WE WERE DIRECTED BY THE TWR TO A HDG AND FREQ CHANGE. WE WENT TO 5000 FT AS DIRECTED AND 270 DEGS. AT 5000 FT I DECIDED TO ENGAGE #2 AUTOPLT (#1 INOP). THE FMA SHOWED HDG SELECT AND ALT HOLD. THEN I NOTICED THE ALT WAS GOING ABOUT 100 FT LOW. I TRIED TO CORRECT BY ADJUSTING THE VERT SPD WHEEL. I COULD NOT MOVE IT. I DISCONNECTED THE AUTOPLT AND FLEW THE ACFT TO 5000 FT. WE GOT AS LOW AS 4700 FT. THE VERT SPD WHEEL WAS FROZEN AT FULL DOWN POS TO THE GATE. INFO: #1 FLT DIRECTOR WAS PLACARDED INOP. THE CAPT SIDE WAS BOOTSTRAPPED TO THE COPLT'S. AFTER TKOF FROM LAX, I NOTICED THAT WHILE HAND-FLYING USING THE FLT DIRECTOR, THE VERT SPD WHEEL WAS NOT WORKING AS WELL AS IT SHOULD, BUT WHEN THE #2 AUTOPLT WAS ENGAGED (#1 AUTOPLT INOP AND PLACARDED), THE VERT SPD WHEEL WORKED JUST FINE. I WROTE UP THE SYS GOING INTO DFW. AFTER EXECUTING THE GAR AT DFW, THE TWR ASKED IF WE NEEDED ASSISTANCE. I GUESS HE DIDN'T REALIZE WHY I TOOK IT AROUND. SUPPLEMENTAL INFO FROM ACN 225482: WITH #1 AUTOPLT ENGAGED IN ALT HOLD MODE AT 5000 FT MSL, THE ACFT BEGAN A SLOW DSCNT AT WHICH POINT THE CAPT DISCONNECTED THE AUTOPLT AND RECAPTURED THE ASSIGNED ALT. MAX DEV WAS 300 FT. (THERE WERE SEVERAL MEL'ED ITEMS ASSOCIATED WITH THE FMS ON THIS ACFT, BUT DURING THIS HIGH WORKLOAD SITUATION WE WERE UNABLE TO MONITOR THE ACFT AS DESIRED.)

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.