Air carrier large transport flight crew complaint about an erratic glide slope during an ILS approac...

Attributes
ACN	158788
Time
Date	199010
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dfw
State Reference	TX
Altitude	agl bound lower : 1000 agl bound upper : 1000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : dfw tower : crg
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 210 flight time total : 6000
ASRS Report	158788
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	non adherence : published procedure other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Weather
Air Traffic Incident	other
Situations
ATC Facility	procedure or policy : unspecified

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.

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.

Air carrier large transport flight crew complaint about an erratic glide slope during an ILS approach into dfw. ATCT local controller had allowed a widebody transport to taxi thus disrupting the glide slope signal.