Narrative:

We were flying from mem to dfw with dfw at low minimums due to fog. During our trip, dfw was at CAT 3 conditions and we briefed the CAT 3 (autoland) approach. Dfw was landing south. Passing byp on the arrival, dfw came up to 1600 ft RVR for runway 17L. We decided to continue the autoland as planned. WX on the arrival was VFR with clear skies and 10+ mi visibility. The problem at dfw was localized ground fog and 100 ft ceilings, with tops around 500 ft. On base leg to ILS runway 17L, we were vectored at 4000 ft in clear VFR on top conditions with unlimited visibility. The first officer reported that he was not getting a good identify on either ILS receiver. I checked and got a weak and intermittent identify. We decided to continue after both confirming that we were both tuned to 111.75 and 174 degrees for ILS runway 17L. All traffic on our frequency was behind us, and I got the impression we were the first to fly the approach to runway 17L. The controller turned us to dogleg to intercept right around draak at 4000 ft. The identify started to get stronger as the controller cleared us to intercept the ILS, maintain 4000 ft until established. First officer reported he was now getting a good identify and both our 'off' flags had retracted. As our dogleg approached the FMS course line, I turned to 174 degree heading and selected localizer then autoland. The FMA showed 'localizer cap' indicating it was capturing the localizer. I was aligned on course and the CDI was centered. The GS was descending and failed to capture, so with about 1/2 DOT above GS I began a manual descent to capture it. We were descending out of 4000 ft above clouds in VFR conditions. Suddenly the airplane, still on autoplt, made a sharp right turn (west) and began turning away from the course on the navigation display. I was looking outside and clearing and didn't notice what the CDI displayed. I disengaged the autoplt and turned back towards the final approach course just as approach control called us and asked if we were established. The controller climbed us back to 4000 ft and turned us east, away from the airport and vectored us around for another approach. We told him we had trouble with the identify and a fluctuating course and GS. Another aircraft that had been behind us was vectored to final and had no trouble. We subsequently intercepted with a much stronger identify and shot the approach full autoland with no incidents. On short final we noticed a truck and workmen on the approach lights and decided the approach zone had not been sterile, possibly causing our problems, but I was paged in the terminal and asked to call mr X at approach control. Mr Y is a supervisor controller and apologized to me. He said the ILS had been previously shut down for work on the approach lights, and the ILS had been turned around to runway 35R while the lighting repairs were made. The ILS had not been turned back to runway 17L while we were making the first approach. He apologized for that, but chided me for leaving 4000 ft before we were fully established. I explained that we were receiving an identify and thought we were established (until the radical right turn) and must have been locked on the back course, but I don't think he fully understood me. I thanked him for his apology, and he reiterated the dangers of descending prior to being established. Lessons learned: I think I got the proper identify for the runway, ippz, but I am not positive. If the ILS was turned around and we were receiving the runway 35R identify, iajq, we failed to notice. I only descended from 4000 ft to chase the GS because we were in visual conditions at the time and I thought we were established on course. But next time I need to be more certain of course capture before starting down. We should also have been more forceful with the controller when he queried about the initial bad idents. Supplemental information from acn 632921: just prior to getting handed off to the tower, we asked the controller what had happened with the localizer. He did not give us any specifics, but said that they had to do 'something' to make it usable. It was not until after captain had called the controller on the ground that we found out that the localizer had been turned around to the runway 35R side because ground crews were working on the runway 17L approach lights. Upon reflection, I realize that we probably never got an accurate identify on the localizer for runway 17L, since it seems that the localizer was turned around to runway 35R, which has a different identify. I listened to that identify at least 5 times prior to the first attempt at intercept, and I was sure that I had heard it correctly, although it was faint. That should have been a clue that something was amiss.

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Original NASA ASRS Text

Title: MD83 CREW WAS CLRED FOR A CAT 3 AUTOLAND APCH ON RWY 17L AT DFW WITH THE ILS TUNED TO RWY 35R.

Narrative: WE WERE FLYING FROM MEM TO DFW WITH DFW AT LOW MINIMUMS DUE TO FOG. DURING OUR TRIP, DFW WAS AT CAT 3 CONDITIONS AND WE BRIEFED THE CAT 3 (AUTOLAND) APCH. DFW WAS LNDG S. PASSING BYP ON THE ARR, DFW CAME UP TO 1600 FT RVR FOR RWY 17L. WE DECIDED TO CONTINUE THE AUTOLAND AS PLANNED. WX ON THE ARR WAS VFR WITH CLR SKIES AND 10+ MI VISIBILITY. THE PROB AT DFW WAS LOCALIZED GND FOG AND 100 FT CEILINGS, WITH TOPS AROUND 500 FT. ON BASE LEG TO ILS RWY 17L, WE WERE VECTORED AT 4000 FT IN CLR VFR ON TOP CONDITIONS WITH UNLIMITED VISIBILITY. THE FO RPTED THAT HE WAS NOT GETTING A GOOD IDENT ON EITHER ILS RECEIVER. I CHKED AND GOT A WEAK AND INTERMITTENT IDENT. WE DECIDED TO CONTINUE AFTER BOTH CONFIRMING THAT WE WERE BOTH TUNED TO 111.75 AND 174 DEGS FOR ILS RWY 17L. ALL TFC ON OUR FREQ WAS BEHIND US, AND I GOT THE IMPRESSION WE WERE THE FIRST TO FLY THE APCH TO RWY 17L. THE CTLR TURNED US TO DOGLEG TO INTERCEPT R AROUND DRAAK AT 4000 FT. THE IDENT STARTED TO GET STRONGER AS THE CTLR CLRED US TO INTERCEPT THE ILS, MAINTAIN 4000 FT UNTIL ESTABLISHED. FO RPTED HE WAS NOW GETTING A GOOD IDENT AND BOTH OUR 'OFF' FLAGS HAD RETRACTED. AS OUR DOGLEG APCHED THE FMS COURSE LINE, I TURNED TO 174 DEG HDG AND SELECTED LOC THEN AUTOLAND. THE FMA SHOWED 'LOC CAP' INDICATING IT WAS CAPTURING THE LOC. I WAS ALIGNED ON COURSE AND THE CDI WAS CTRED. THE GS WAS DSNDING AND FAILED TO CAPTURE, SO WITH ABOUT 1/2 DOT ABOVE GS I BEGAN A MANUAL DSCNT TO CAPTURE IT. WE WERE DSNDING OUT OF 4000 FT ABOVE CLOUDS IN VFR CONDITIONS. SUDDENLY THE AIRPLANE, STILL ON AUTOPLT, MADE A SHARP R TURN (W) AND BEGAN TURNING AWAY FROM THE COURSE ON THE NAV DISPLAY. I WAS LOOKING OUTSIDE AND CLRING AND DIDN'T NOTICE WHAT THE CDI DISPLAYED. I DISENGAGED THE AUTOPLT AND TURNED BACK TOWARDS THE FINAL APCH COURSE JUST AS APCH CTL CALLED US AND ASKED IF WE WERE ESTABLISHED. THE CTLR CLBED US BACK TO 4000 FT AND TURNED US E, AWAY FROM THE ARPT AND VECTORED US AROUND FOR ANOTHER APCH. WE TOLD HIM WE HAD TROUBLE WITH THE IDENT AND A FLUCTUATING COURSE AND GS. ANOTHER ACFT THAT HAD BEEN BEHIND US WAS VECTORED TO FINAL AND HAD NO TROUBLE. WE SUBSEQUENTLY INTERCEPTED WITH A MUCH STRONGER IDENT AND SHOT THE APCH FULL AUTOLAND WITH NO INCIDENTS. ON SHORT FINAL WE NOTICED A TRUCK AND WORKMEN ON THE APCH LIGHTS AND DECIDED THE APCH ZONE HAD NOT BEEN STERILE, POSSIBLY CAUSING OUR PROBS, BUT I WAS PAGED IN THE TERMINAL AND ASKED TO CALL MR X AT APCH CTL. MR Y IS A SUPVR CTLR AND APOLOGIZED TO ME. HE SAID THE ILS HAD BEEN PREVIOUSLY SHUT DOWN FOR WORK ON THE APCH LIGHTS, AND THE ILS HAD BEEN TURNED AROUND TO RWY 35R WHILE THE LIGHTING REPAIRS WERE MADE. THE ILS HAD NOT BEEN TURNED BACK TO RWY 17L WHILE WE WERE MAKING THE FIRST APCH. HE APOLOGIZED FOR THAT, BUT CHIDED ME FOR LEAVING 4000 FT BEFORE WE WERE FULLY ESTABLISHED. I EXPLAINED THAT WE WERE RECEIVING AN IDENT AND THOUGHT WE WERE ESTABLISHED (UNTIL THE RADICAL R TURN) AND MUST HAVE BEEN LOCKED ON THE BACK COURSE, BUT I DON'T THINK HE FULLY UNDERSTOOD ME. I THANKED HIM FOR HIS APOLOGY, AND HE REITERATED THE DANGERS OF DSNDING PRIOR TO BEING ESTABLISHED. LESSONS LEARNED: I THINK I GOT THE PROPER IDENT FOR THE RWY, IPPZ, BUT I AM NOT POSITIVE. IF THE ILS WAS TURNED AROUND AND WE WERE RECEIVING THE RWY 35R IDENT, IAJQ, WE FAILED TO NOTICE. I ONLY DSNDED FROM 4000 FT TO CHASE THE GS BECAUSE WE WERE IN VISUAL CONDITIONS AT THE TIME AND I THOUGHT WE WERE ESTABLISHED ON COURSE. BUT NEXT TIME I NEED TO BE MORE CERTAIN OF COURSE CAPTURE BEFORE STARTING DOWN. WE SHOULD ALSO HAVE BEEN MORE FORCEFUL WITH THE CTLR WHEN HE QUERIED ABOUT THE INITIAL BAD IDENTS. SUPPLEMENTAL INFO FROM ACN 632921: JUST PRIOR TO GETTING HANDED OFF TO THE TWR, WE ASKED THE CTLR WHAT HAD HAPPENED WITH THE LOC. HE DID NOT GIVE US ANY SPECIFICS, BUT SAID THAT THEY HAD TO DO 'SOMETHING' TO MAKE IT USABLE. IT WAS NOT UNTIL AFTER CAPT HAD CALLED THE CTLR ON THE GND THAT WE FOUND OUT THAT THE LOC HAD BEEN TURNED AROUND TO THE RWY 35R SIDE BECAUSE GND CREWS WERE WORKING ON THE RWY 17L APCH LIGHTS. UPON REFLECTION, I REALIZE THAT WE PROBABLY NEVER GOT AN ACCURATE IDENT ON THE LOC FOR RWY 17L, SINCE IT SEEMS THAT THE LOC WAS TURNED AROUND TO RWY 35R, WHICH HAS A DIFFERENT IDENT. I LISTENED TO THAT IDENT AT LEAST 5 TIMES PRIOR TO THE FIRST ATTEMPT AT INTERCEPT, AND I WAS SURE THAT I HAD HEARD IT CORRECTLY, ALTHOUGH IT WAS FAINT. THAT SHOULD HAVE BEEN A CLUE THAT SOMETHING WAS AMISS.

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.