Narrative:

During an ILS approach to runway 17C at dfw we received erroneous GS indications and performed a missed approach. We were initially assigned 5000 ft until established on the localizer and cleared for the ILS approach. Once established on the approach the autoplt pitched down abruptly, chasing the GS. The first officer turned the autoplt off and began hand-flying. We noticed the proceeding aircraft informed the tower that they were low but showing on the GS. Both the first officer and I heard this and thought to give the GS extra scrutiny. The tower told the proceeding aircraft that an airplane was on taxiway Z and that was the reason for the GS discrepancy. The aircraft continued and landed. We noticed we were below the proper glide path approximately at the FAF. The reported WX was scattered clouds at 1000 ft and I began to look for the runway. Also at this time, the tower called us, a few seconds later, approach called us. I answered both times, but neither of them called back. I asked for a current altimeter setting and was given the same setting we already had. The GS abruptly went full scale deflection and we were no longer sure if we were anywhere close to the proper glide path, so we executed a missed approach. We were then vectored for an ILS to runway 18R with an uneventful landing. We later departed dfw on runway 17R and we noticed a lot of construction equipment between runway 17R and the approach lighting system for runway 17C. It's very possible due to the construction and, more likely, the presence of an aircraft on taxiway Z that we received massive GS signal errors. Supplemental information from acn 635074: when we crossed the FAF we were approximately 1700 ft. The chart showed a crossing altitude of 2275 ft. We commented that we were low, but all indications were normal. We then executed a missed approach at less than 1000 ft because our position was in doubt and we did not have the field visually. We went around and landed uneventfully on runway 18R. Callback conversation with reporter on acn 635073 revealed the following information: callback with reporter did not add any new information.

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Original NASA ASRS Text

Title: CRJ CREW ON AN ILS APCH AT DFW TO RWY 17C EXPERIENCE ERRONEOUS GS INDICATIONS AND PERFORM A MISSED APCH.

Narrative: DURING AN ILS APCH TO RWY 17C AT DFW WE RECEIVED ERRONEOUS GS INDICATIONS AND PERFORMED A MISSED APCH. WE WERE INITIALLY ASSIGNED 5000 FT UNTIL ESTABLISHED ON THE LOC AND CLRED FOR THE ILS APCH. ONCE ESTABLISHED ON THE APCH THE AUTOPLT PITCHED DOWN ABRUPTLY, CHASING THE GS. THE FO TURNED THE AUTOPLT OFF AND BEGAN HAND-FLYING. WE NOTICED THE PROCEEDING ACFT INFORMED THE TWR THAT THEY WERE LOW BUT SHOWING ON THE GS. BOTH THE FO AND I HEARD THIS AND THOUGHT TO GIVE THE GS EXTRA SCRUTINY. THE TWR TOLD THE PROCEEDING ACFT THAT AN AIRPLANE WAS ON TXWY Z AND THAT WAS THE REASON FOR THE GS DISCREPANCY. THE ACFT CONTINUED AND LANDED. WE NOTICED WE WERE BELOW THE PROPER GLIDE PATH APPROX AT THE FAF. THE RPTED WX WAS SCATTERED CLOUDS AT 1000 FT AND I BEGAN TO LOOK FOR THE RWY. ALSO AT THIS TIME, THE TWR CALLED US, A FEW SECONDS LATER, APCH CALLED US. I ANSWERED BOTH TIMES, BUT NEITHER OF THEM CALLED BACK. I ASKED FOR A CURRENT ALTIMETER SETTING AND WAS GIVEN THE SAME SETTING WE ALREADY HAD. THE GS ABRUPTLY WENT FULL SCALE DEFLECTION AND WE WERE NO LONGER SURE IF WE WERE ANYWHERE CLOSE TO THE PROPER GLIDE PATH, SO WE EXECUTED A MISSED APCH. WE WERE THEN VECTORED FOR AN ILS TO RWY 18R WITH AN UNEVENTFUL LNDG. WE LATER DEPARTED DFW ON RWY 17R AND WE NOTICED A LOT OF CONSTRUCTION EQUIP BTWN RWY 17R AND THE APCH LIGHTING SYS FOR RWY 17C. IT'S VERY POSSIBLE DUE TO THE CONSTRUCTION AND, MORE LIKELY, THE PRESENCE OF AN ACFT ON TXWY Z THAT WE RECEIVED MASSIVE GS SIGNAL ERRORS. SUPPLEMENTAL INFO FROM ACN 635074: WHEN WE CROSSED THE FAF WE WERE APPROX 1700 FT. THE CHART SHOWED A XING ALT OF 2275 FT. WE COMMENTED THAT WE WERE LOW, BUT ALL INDICATIONS WERE NORMAL. WE THEN EXECUTED A MISSED APCH AT LESS THAN 1000 FT BECAUSE OUR POS WAS IN DOUBT AND WE DID NOT HAVE THE FIELD VISUALLY. WE WENT AROUND AND LANDED UNEVENTFULLY ON RWY 18R. CALLBACK CONVERSATION WITH RPTR ON ACN 635073 REVEALED THE FOLLOWING INFO: CALLBACK WITH RPTR DID NOT ADD ANY NEW INFO.

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.