Narrative:

During approach at dfw ILS 17L the autoplt ran away after coupling with the localizer and G/south. WX conditions were IMC and I was unable to announce the problem to regional approach or dfw tower as both hands were busy trying to control the aircraft which was an small transport. The autoplt would not disconnect with the trim switch, F/D switch or trim disconnect switch. The cockpit was too dark and I was too busy flying the aircraft to find the autoplt and trim cbs, although I turned on the overhead light and tried. Callback conversation with reporter revealed the following information. The autoplt on this aircraft is historically slow to intercept the G/south. In this case, aircraft got above the B/south and was descending rapidly to capture. It went through the G/south and kept descending. Reporter tried to override autoplt with pressure on yoke while at same time trying to disengage the autoplt by actuating the elevator trim switch. This failed to work, the autoplt remained engaged. The reporter next tried to find the trim circuit breaker's but was unable. He should have turned off the F/D which should have also disengaged the autoplt but he didn't think to do this. During all this, the aircraft got below G/south and well to right of localizer. Reporter broke out of clouds lined up with runway 17R versus 17L and elected to land on runway 17R which he did. He was unable to tell the tower of his intentions because of frequency congestion and a problem with his #2 communication radio. He was asked to call the tower by phone.

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Original NASA ASRS Text

Title: SMT PLT UNABLE TO DISENGGE AUTOPLT DURING COUPLED APCH LANDS ON WRONG RWY.

Narrative: DURING APCH AT DFW ILS 17L THE AUTOPLT RAN AWAY AFTER COUPLING WITH THE LOC AND G/S. WX CONDITIONS WERE IMC AND I WAS UNABLE TO ANNOUNCE THE PROB TO REGIONAL APCH OR DFW TWR AS BOTH HANDS WERE BUSY TRYING TO CTL THE ACFT WHICH WAS AN SMT. THE AUTOPLT WOULD NOT DISCONNECT WITH THE TRIM SWITCH, F/D SWITCH OR TRIM DISCONNECT SWITCH. THE COCKPIT WAS TOO DARK AND I WAS TOO BUSY FLYING THE ACFT TO FIND THE AUTOPLT AND TRIM CBS, ALTHOUGH I TURNED ON THE OVERHEAD LIGHT AND TRIED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. THE AUTOPLT ON THIS ACFT IS HISTORICALLY SLOW TO INTERCEPT THE G/S. IN THIS CASE, ACFT GOT ABOVE THE B/S AND WAS DSNDING RAPIDLY TO CAPTURE. IT WENT THROUGH THE G/S AND KEPT DSNDING. RPTR TRIED TO OVERRIDE AUTOPLT WITH PRESSURE ON YOKE WHILE AT SAME TIME TRYING TO DISENGAGE THE AUTOPLT BY ACTUATING THE ELEVATOR TRIM SWITCH. THIS FAILED TO WORK, THE AUTOPLT REMAINED ENGAGED. THE RPTR NEXT TRIED TO FIND THE TRIM CB'S BUT WAS UNABLE. HE SHOULD HAVE TURNED OFF THE F/D WHICH SHOULD HAVE ALSO DISENGAGED THE AUTOPLT BUT HE DIDN'T THINK TO DO THIS. DURING ALL THIS, THE ACFT GOT BELOW G/S AND WELL TO R OF LOC. RPTR BROKE OUT OF CLOUDS LINED UP WITH RWY 17R VERSUS 17L AND ELECTED TO LAND ON RWY 17R WHICH HE DID. HE WAS UNABLE TO TELL THE TWR OF HIS INTENTIONS BECAUSE OF FREQ CONGESTION AND A PROB WITH HIS #2 COM RADIO. HE WAS ASKED TO CALL THE TWR BY PHONE.

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.