Narrative:

We were executing an ILS runway 17L CAT III to dfw. We turned to final at 15 DME and crossed penny at 4000 ft. Clearance was to maintain 4000 ft until established, cleared for approach. Autoplt captured GS from above (about only 1/3 DOT). Localizer and slope appeared normal, but aircraft crossed jiffy at 1400 ft AGL versus 1713 ft, descending at 1500 FPM. I told the first officer 'let's go around.' he executed go around at about 1200 ft, followed by radar vectors to uneventful ILS CAT 1 to runway 17L. As we were climbing, we heard tower call the aircraft behind us well below GS, and then a few seconds later repeated the call and told them to climb immediately. It is likely the 2 occurrences were related. Possible reasons for the problems might have been a blanking of the ILS signal, or getting wrong sensing because of the sharp turn at 15 DME, 4000 ft just as the autoplt is capturing the GS instead of being established on final and capturing from below. Supplemental information from acn 236400: taxiing from east air freight ramp. We were told to hold short of runway 13L. After about 20 mins we were told by dfw ground to taxi across runway 13L, turn left and then hold short of runway 17L on taxiway 19 and to expect runway 17L for takeoff. After about 5 mins in holding short position, we heard on tower frequency, which we had been instructed to monitor, that at least 2 airplanes found themselves low over the marker and were executing missed approachs. Tower then instructed us to cross runway 17L and told us we had obstructed the ILS GS antenna. Commuter aircraft were taxiing to runway 13L on taxiway 18 and one of them notified tower that the ILS hold short markers were removed due to construction on a new taxiway parallel to runway 17L. Departure ATIS did not mention which ILS's were in progress, but we saw aircraft landing on runway 17L when we taxied on to taxiway 19, and a closer look at the taxi chart would have told us that our ground clearance might have been questionable. Since our clearance onto taxiway 19 made us cross the ILS hold line (based on taxi chart) the captain was under the impression that we would get a quick takeoff clearance since ground cleared us onto taxiway 19. We were in a widebody transport fgt. Callback conversation with reporter revealed the following information: analyst call to airport operations revealed that although there was some construction work being accomplished in the area, the runway and ILS hold lines were in place as required.

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Original NASA ASRS Text

Title: AN ACR MLG MADE A GAR UPON FINDING ITSELF LOW OVER THE OM.

Narrative: WE WERE EXECUTING AN ILS RWY 17L CAT III TO DFW. WE TURNED TO FINAL AT 15 DME AND CROSSED PENNY AT 4000 FT. CLRNC WAS TO MAINTAIN 4000 FT UNTIL ESTABLISHED, CLRED FOR APCH. AUTOPLT CAPTURED GS FROM ABOVE (ABOUT ONLY 1/3 DOT). LOC AND SLOPE APPEARED NORMAL, BUT ACFT CROSSED JIFFY AT 1400 FT AGL VERSUS 1713 FT, DSNDING AT 1500 FPM. I TOLD THE FO 'LET'S GAR.' HE EXECUTED GAR AT ABOUT 1200 FT, FOLLOWED BY RADAR VECTORS TO UNEVENTFUL ILS CAT 1 TO RWY 17L. AS WE WERE CLBING, WE HEARD TWR CALL THE ACFT BEHIND US WELL BELOW GS, AND THEN A FEW SECONDS LATER REPEATED THE CALL AND TOLD THEM TO CLB IMMEDIATELY. IT IS LIKELY THE 2 OCCURRENCES WERE RELATED. POSSIBLE REASONS FOR THE PROBS MIGHT HAVE BEEN A BLANKING OF THE ILS SIGNAL, OR GETTING WRONG SENSING BECAUSE OF THE SHARP TURN AT 15 DME, 4000 FT JUST AS THE AUTOPLT IS CAPTURING THE GS INSTEAD OF BEING ESTABLISHED ON FINAL AND CAPTURING FROM BELOW. SUPPLEMENTAL INFO FROM ACN 236400: TAXIING FROM E AIR FREIGHT RAMP. WE WERE TOLD TO HOLD SHORT OF RWY 13L. AFTER ABOUT 20 MINS WE WERE TOLD BY DFW GND TO TAXI ACROSS RWY 13L, TURN L AND THEN HOLD SHORT OF RWY 17L ON TXWY 19 AND TO EXPECT RWY 17L FOR TKOF. AFTER ABOUT 5 MINS IN HOLDING SHORT POS, WE HEARD ON TWR FREQ, WHICH WE HAD BEEN INSTRUCTED TO MONITOR, THAT AT LEAST 2 AIRPLANES FOUND THEMSELVES LOW OVER THE MARKER AND WERE EXECUTING MISSED APCHS. TWR THEN INSTRUCTED US TO CROSS RWY 17L AND TOLD US WE HAD OBSTRUCTED THE ILS GS ANTENNA. COMMUTER ACFT WERE TAXIING TO RWY 13L ON TXWY 18 AND ONE OF THEM NOTIFIED TWR THAT THE ILS HOLD SHORT MARKERS WERE REMOVED DUE TO CONSTRUCTION ON A NEW TXWY PARALLEL TO RWY 17L. DEP ATIS DID NOT MENTION WHICH ILS'S WERE IN PROGRESS, BUT WE SAW ACFT LNDG ON RWY 17L WHEN WE TAXIED ON TO TXWY 19, AND A CLOSER LOOK AT THE TAXI CHART WOULD HAVE TOLD US THAT OUR GND CLRNC MIGHT HAVE BEEN QUESTIONABLE. SINCE OUR CLRNC ONTO TXWY 19 MADE US CROSS THE ILS HOLD LINE (BASED ON TAXI CHART) THE CAPT WAS UNDER THE IMPRESSION THAT WE WOULD GET A QUICK TKOF CLRNC SINCE GND CLRED US ONTO TXWY 19. WE WERE IN A WDB FGT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ANALYST CALL TO ARPT OPS REVEALED THAT ALTHOUGH THERE WAS SOME CONSTRUCTION WORK BEING ACCOMPLISHED IN THE AREA, THE RWY AND ILS HOLD LINES WERE IN PLACE AS REQUIRED.

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.