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An air carrier medium large transport makes an approach into phl using a false GS indication. The crew's flight directors were being used but were not following the real GS signal which indicated out of sight in the tops of the ADI's.
| Attributes | |
| ACN | 399889 |
| Time | |
| Date | 199804 |
| Day | Wed |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : phl |
| State Reference | PA |
| Altitude | msl bound lower : 4000 msl bound upper : 4000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : phl |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : approach |
| Route In Use | arrival other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 250 flight time total : 15000 |
| ASRS Report | 399889 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument |
| Events | |
| Anomaly | non adherence : far non adherence : published procedure non adherence : clearance |
| Independent Detector | atc equipment other atc equipment : unspecified other controllera |
| Resolutory Action | flight crew : returned to intended course or assigned course other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
At approximately 12 mi out we were cleared for the ILS approach. I selected flight director command steering bars. I was on course and started following GS steering bar. We did not notice that the raw data GS indicators were not present on the ADI's or the HSI's. We both thought they might be stuck and began tapping the instruments. We broke out of the clouds and observed that we were somewhat low on visual glidepath. At about the same time, approach controller called us with a 'low altitude alert.' I leveled off and regained a visual glidepath and then we saw the GS indicators (raw data) come down from the top of the instrument cases. Landing was uneventful. We were actually flying a parallel GS. Erred by 1) following flight director without first checking for flight director 'GS armed' annunciator and GS captured annunciator, and 2) xchking raw data GS indicators.
Original NASA ASRS Text
Title: AN ACR MLG MAKES AN APCH INTO PHL USING A FALSE GS INDICATION. THE CREW'S FLT DIRECTORS WERE BEING USED BUT WERE NOT FOLLOWING THE REAL GS SIGNAL WHICH INDICATED OUT OF SIGHT IN THE TOPS OF THE ADI'S.
Narrative: AT APPROX 12 MI OUT WE WERE CLRED FOR THE ILS APCH. I SELECTED FLT DIRECTOR COMMAND STEERING BARS. I WAS ON COURSE AND STARTED FOLLOWING GS STEERING BAR. WE DID NOT NOTICE THAT THE RAW DATA GS INDICATORS WERE NOT PRESENT ON THE ADI'S OR THE HSI'S. WE BOTH THOUGHT THEY MIGHT BE STUCK AND BEGAN TAPPING THE INSTS. WE BROKE OUT OF THE CLOUDS AND OBSERVED THAT WE WERE SOMEWHAT LOW ON VISUAL GLIDEPATH. AT ABOUT THE SAME TIME, APCH CTLR CALLED US WITH A 'LOW ALT ALERT.' I LEVELED OFF AND REGAINED A VISUAL GLIDEPATH AND THEN WE SAW THE GS INDICATORS (RAW DATA) COME DOWN FROM THE TOP OF THE INST CASES. LNDG WAS UNEVENTFUL. WE WERE ACTUALLY FLYING A PARALLEL GS. ERRED BY 1) FOLLOWING FLT DIRECTOR WITHOUT FIRST CHKING FOR FLT DIRECTOR 'GS ARMED' ANNUNCIATOR AND GS CAPTURED ANNUNCIATOR, AND 2) XCHKING RAW DATA GS INDICATORS.
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.