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B737-300 flight crew reports descending below a normal approach path during a visual approach when the glide slope bar freezes in the centered position. The first officer's indications function normally; but are not being monitored and the low approach is not detected until five miles from the field at 1;100 ft.
| Attributes | |
| ACN | 1022040 |
| Time | |
| Date | 201207 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Initial Approach |
| Route In Use | Visual Approach |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | ILS/VOR |
| Person 1 | |
| Function | Pilot Flying Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 151 Flight Crew Type 14000 |
| Person 2 | |
| Function | Pilot Not Flying First Officer |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Procedural FAR Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT |
Narrative:
Cleared visual approach in VMC; autopilot engaged; intercepted heading in descent out of about 3;000 ft; glide slope centered; and set zero altitude when cleared for visual. VOR/localizer captured; pressed app; and glide slope captured. Then; about 1;100 ft five miles out; I realized the runway looked a little flat; disconnected autopilot; and leveled off. Then; got an altitude alert from tower; but had already leveled off; and continued to intercept normal glide path for normal landing. Glide slope needle was stuck on center indicating we were on path and autopilot was coupled. We recycled my HSI switch and then got an accurate glide slope reading; so must not have been a signal problem. First officer's glide slope was working properly. Did not write it up because recycling the HSI switch fixed the problem and could not duplicate the sticking. Never thought an autopilot would couple to a stuck glide slope needle. I should have set 1;500 ft FAF altitude in the window and crosschecked with DME. Better crew coordination of cross checking glide slope needles and call outs would have also helped.
Original NASA ASRS Text
Title: B737-300 flight crew reports descending below a normal approach path during a visual approach when the glide slope bar freezes in the centered position. The First Officer's indications function normally; but are not being monitored and the low approach is not detected until five miles from the field at 1;100 FT.
Narrative: Cleared visual approach in VMC; autopilot engaged; intercepted heading in descent out of about 3;000 FT; glide slope centered; and set zero altitude when cleared for visual. VOR/LOC captured; pressed APP; and glide slope captured. Then; about 1;100 FT five miles out; I realized the runway looked a little flat; disconnected autopilot; and leveled off. Then; got an altitude alert from Tower; but had already leveled off; and continued to intercept normal glide path for normal landing. Glide slope needle was stuck on center indicating we were on path and autopilot was coupled. We recycled my HSI switch and then got an accurate glide slope reading; so must not have been a signal problem. First Officer's glide slope was working properly. Did not write it up because recycling the HSI switch fixed the problem and could not duplicate the sticking. Never thought an autopilot would couple to a stuck glide slope needle. I should have set 1;500 FT FAF altitude in the window and crosschecked with DME. Better crew coordination of cross checking glide slope needles and call outs would have also helped.
Data retrieved from NASA's ASRS site as of July 2013 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.