Narrative:

Approach to dfw on 10/90 runway 18R ILS. ATIS showed VFR 15 scattered 7 mi wind 170/08. Estimate actual conditions 450' ceiling and 2 mi visibility. With rain. We were cleared ILS approach to runway 18R, experienced IFR conditions from 15000' to 400' al. After passing the FAF very subtle G/south signal deviations began to occur. These anomalies were not readily apparent at first. We finally recognized that the G/south was unreliable and leveled off at 1000' MSL which was above localizer only minimums, still IFR. The G/south by this time went through full scale deflection both up and down. Runway was then in sight and landed normally. After clearing the active runway, we gave a PIREP to tower saying the ceiling was approximately 400' and IFR and also we experienced G/south problems. Tower said their information was that WX. 18 broken and 7 mi and that they weren't required to protect the ILS signal since it was VFR (which it wasn't). They (tower) said our G/south problem was due to a widebody transport being cleared into position on runway 18L. Tower was very defensive about our comments and basically ignored them. I expect the ILS signal to be protected when IFR in conditions like the above. We never saw any off flags on our G/south presentation.

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Original NASA ASRS Text

Title: ACR LGT FLT CREW COMPLAINT ABOUT AN ERRATIC GLIDE SLOPE DURING AN ILS APCH INTO DFW. ATCT LCL CTLR HAD ALLOWED A WDB TO TAXI THUS DISRUPTING THE GLIDE SLOPE SIGNAL.

Narrative: APCH TO DFW ON 10/90 RWY 18R ILS. ATIS SHOWED VFR 15 SCATTERED 7 MI WIND 170/08. ESTIMATE ACTUAL CONDITIONS 450' CEILING AND 2 MI VISIBILITY. WITH RAIN. WE WERE CLRED ILS APCH TO RWY 18R, EXPERIENCED IFR CONDITIONS FROM 15000' TO 400' AL. AFTER PASSING THE FAF VERY SUBTLE G/S SIGNAL DEVS BEGAN TO OCCUR. THESE ANOMALIES WERE NOT READILY APPARENT AT FIRST. WE FINALLY RECOGNIZED THAT THE G/S WAS UNRELIABLE AND LEVELED OFF AT 1000' MSL WHICH WAS ABOVE LOC ONLY MINIMUMS, STILL IFR. THE G/S BY THIS TIME WENT THROUGH FULL SCALE DEFLECTION BOTH UP AND DOWN. RWY WAS THEN IN SIGHT AND LANDED NORMALLY. AFTER CLRING THE ACTIVE RWY, WE GAVE A PIREP TO TWR SAYING THE CEILING WAS APPROX 400' AND IFR AND ALSO WE EXPERIENCED G/S PROBS. TWR SAID THEIR INFO WAS THAT WX. 18 BROKEN AND 7 MI AND THAT THEY WEREN'T REQUIRED TO PROTECT THE ILS SIGNAL SINCE IT WAS VFR (WHICH IT WASN'T). THEY (TWR) SAID OUR G/S PROB WAS DUE TO A WDB BEING CLRED INTO POS ON RWY 18L. TWR WAS VERY DEFENSIVE ABOUT OUR COMMENTS AND BASICALLY IGNORED THEM. I EXPECT THE ILS SIGNAL TO BE PROTECTED WHEN IFR IN CONDITIONS LIKE THE ABOVE. WE NEVER SAW ANY OFF FLAGS ON OUR G/S PRESENTATION.

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.