Narrative:

The arrival ATIS reported VFR conditions at the field with a ceiling of 2800 ft, and the GS inoperative for runway 18R. The visual approach with a localizer backup was briefed for runway 18R (no DME). On downwind, abeam the runway 18R LOM, addys, the PNF tuned and idented the localizer and LOM frequencys. On dogleg, at 2500 ft MSL, the clearance was given to maintain 2100 ft until established, maintain 180 KTS until addys, cleared the ILS runway 18R approach. I selected the approach mode for the flight director upon receiving clearance, and intercepted the final approach course at 2100 ft MSL. There were no GS off flags in view on the HSI. The flight director commanded a descent and showed 1 DOT plus high on the GS. I began a gradual descent and at some point asked the PNF to ask about the status of the GS. As I transitioned my scan to outside the cockpit, I noticed the picture being flat and the runway was not easy to discern. At some point, the PNF called the traffic ahead and attention was diverted to the TCASII to determine proper spacing. At approximately 1850 ft MSL, the approach controller issued an altitude alert warning and I corrected back to 2100 ft. The PNF asked the status of the GS and the controller reported it as being operational. 2 other aircraft on frequency immediately reported the altitude guidance of the GS as being erroneous. The controller then said he was in error and that the GS was inoperative. A short time later, the GS off flags appeared in the HSI. The remainder of the approach and landing were uneventful. I feel the following factors contributed to this event: 1) this was the last leg of a 3 day rotation, lax to cvg. As a result crew alertness was impacted, 2) the PNF was not based at cvg and was more familiar with east coast shuttle flying, 3) I should have asked the PNF to remain on the VOR for DME information until turning base, which is my normal habit pattern, 4) although we were aware we were outside the LOM, descent was begun out of 2100 ft due to the habit of selecting the flight director approach mode upon receiving clearance for the approach. This commands an intercept to the course and GS. Responding to the cross bars overrode other factors, impacting situational awareness, 5) since visual conditions were reported at the field, we did not give a high priority to xchking the GS crossing altitude at the LOM against the flight director command and our relative position to the LOM, 6) the absence of GS off flags in the HSI and the verified good identify for the localizer, failed to alert us to the fact the GS information was still unreliable, 7) a slow transition to a visual picture outside the cockpit prevented an earlier realization of the erroneous GS data, 8) overcast WX conditions did not permit optimum visual identify of visual cues that would normally have been present.

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Original NASA ASRS Text

Title: FLC DSNDS BELOW INTENDED ALT.

Narrative: THE ARR ATIS RPTED VFR CONDITIONS AT THE FIELD WITH A CEILING OF 2800 FT, AND THE GS INOP FOR RWY 18R. THE VISUAL APCH WITH A LOC BACKUP WAS BRIEFED FOR RWY 18R (NO DME). ON DOWNWIND, ABEAM THE RWY 18R LOM, ADDYS, THE PNF TUNED AND IDENTED THE LOC AND LOM FREQS. ON DOGLEG, AT 2500 FT MSL, THE CLRNC WAS GIVEN TO MAINTAIN 2100 FT UNTIL ESTABLISHED, MAINTAIN 180 KTS UNTIL ADDYS, CLRED THE ILS RWY 18R APCH. I SELECTED THE APCH MODE FOR THE FLT DIRECTOR UPON RECEIVING CLRNC, AND INTERCEPTED THE FINAL APCH COURSE AT 2100 FT MSL. THERE WERE NO GS OFF FLAGS IN VIEW ON THE HSI. THE FLT DIRECTOR COMMANDED A DSCNT AND SHOWED 1 DOT PLUS HIGH ON THE GS. I BEGAN A GRADUAL DSCNT AND AT SOME POINT ASKED THE PNF TO ASK ABOUT THE STATUS OF THE GS. AS I TRANSITIONED MY SCAN TO OUTSIDE THE COCKPIT, I NOTICED THE PICTURE BEING FLAT AND THE RWY WAS NOT EASY TO DISCERN. AT SOME POINT, THE PNF CALLED THE TFC AHEAD AND ATTENTION WAS DIVERTED TO THE TCASII TO DETERMINE PROPER SPACING. AT APPROX 1850 FT MSL, THE APCH CTLR ISSUED AN ALT ALERT WARNING AND I CORRECTED BACK TO 2100 FT. THE PNF ASKED THE STATUS OF THE GS AND THE CTLR RPTED IT AS BEING OPERATIONAL. 2 OTHER ACFT ON FREQ IMMEDIATELY RPTED THE ALT GUIDANCE OF THE GS AS BEING ERRONEOUS. THE CTLR THEN SAID HE WAS IN ERROR AND THAT THE GS WAS INOP. A SHORT TIME LATER, THE GS OFF FLAGS APPEARED IN THE HSI. THE REMAINDER OF THE APCH AND LNDG WERE UNEVENTFUL. I FEEL THE FOLLOWING FACTORS CONTRIBUTED TO THIS EVENT: 1) THIS WAS THE LAST LEG OF A 3 DAY ROTATION, LAX TO CVG. AS A RESULT CREW ALERTNESS WAS IMPACTED, 2) THE PNF WAS NOT BASED AT CVG AND WAS MORE FAMILIAR WITH E COAST SHUTTLE FLYING, 3) I SHOULD HAVE ASKED THE PNF TO REMAIN ON THE VOR FOR DME INFO UNTIL TURNING BASE, WHICH IS MY NORMAL HABIT PATTERN, 4) ALTHOUGH WE WERE AWARE WE WERE OUTSIDE THE LOM, DSCNT WAS BEGUN OUT OF 2100 FT DUE TO THE HABIT OF SELECTING THE FLT DIRECTOR APCH MODE UPON RECEIVING CLRNC FOR THE APCH. THIS COMMANDS AN INTERCEPT TO THE COURSE AND GS. RESPONDING TO THE CROSS BARS OVERRODE OTHER FACTORS, IMPACTING SITUATIONAL AWARENESS, 5) SINCE VISUAL CONDITIONS WERE RPTED AT THE FIELD, WE DID NOT GIVE A HIGH PRIORITY TO XCHKING THE GS XING ALT AT THE LOM AGAINST THE FLT DIRECTOR COMMAND AND OUR RELATIVE POS TO THE LOM, 6) THE ABSENCE OF GS OFF FLAGS IN THE HSI AND THE VERIFIED GOOD IDENT FOR THE LOC, FAILED TO ALERT US TO THE FACT THE GS INFO WAS STILL UNRELIABLE, 7) A SLOW TRANSITION TO A VISUAL PICTURE OUTSIDE THE COCKPIT PREVENTED AN EARLIER REALIZATION OF THE ERRONEOUS GS DATA, 8) OVCST WX CONDITIONS DID NOT PERMIT OPTIMUM VISUAL IDENT OF VISUAL CUES THAT WOULD NORMALLY HAVE BEEN PRESENT.

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.