 |
37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
|
B-737 first officer reported experiencing glide-slope signal errors resulting in a low altitude alert.
| Attributes | |
| ACN | 1673032 |
| Time | |
| Date | 201908 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | PHL.Airport |
| State Reference | PA |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B737-800 |
| 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 | First Officer Pilot Flying |
| Qualification | Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Total 7800 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT |
Narrative:
Cleared for the visual approach to 9R at phl airport. The weather was night VMC with unrestricted visibility and light winds. I was the flying pilot with the autopilot engaged. We were at 2;000 ft. AGL approaching the 9R localizer and GS; I selected approach mode; called for the gear down and flaps to 15. The captain (pilot monitoring) verified the speed (below 200) and selected the flaps to 15. The airplane turned to final; captured the localizer and GS. The airplane started a descent on G/south. Without warning the GS indication deflected instantly to full down. With the autopilot engaged; the airplane abruptly pitched nose down as it attempted to track the errant GS indication. I quickly disconnected the autopilot and arrested the sink rate; leveling at 1;100 ft. AGL. The aural warning of 'sink rate' activated. Once leveled at 1;100 ft. With the autopilot disconnected; the before landing checklist was completed. I flew manually level to intercept the glide path to a landing (followed the VASI). Meanwhile the approach controller told us he had received a low altitude alert and instructed us to contact the tower. Once the captain contacted the tower; we were cleared to land on runway 9R. At 1;000 ft. AGL the airplane was fully configured; on speed and before landing checklist completed. I continued the visual approach to a normal landing. Both the captain and I could not figure out why this event occurred. What makes the glide slope to all of the sudden dive to the bottom of the display?? Either there was a system malfunction; or a truck or airplane drove or taxied across the ILS critical area. (Our assumption).
Original NASA ASRS Text
Title: B-737 First Officer reported experiencing glide-slope signal errors resulting in a low altitude alert.
Narrative: Cleared for the visual approach to 9R at PHL airport. The weather was night VMC with unrestricted visibility and light winds. I was the Flying Pilot with the autopilot engaged. We were at 2;000 ft. AGL approaching the 9R LOC and GS; I selected approach mode; called for the gear down and flaps to 15. The Captain (Pilot Monitoring) verified the speed (below 200) and selected the flaps to 15. The airplane turned to final; captured the LOC and GS. The airplane started a descent on G/S. Without warning the GS indication deflected instantly to full down. With the autopilot engaged; the airplane abruptly pitched nose down as it attempted to track the errant GS indication. I quickly disconnected the autopilot and arrested the sink rate; leveling at 1;100 ft. AGL. The aural warning of 'sink rate' activated. Once leveled at 1;100 ft. with the autopilot disconnected; the Before Landing Checklist was completed. I flew manually level to intercept the glide path to a landing (followed the VASI). Meanwhile the Approach Controller told us he had received a low altitude alert and instructed us to contact the Tower. Once the Captain contacted the Tower; we were cleared to land on Runway 9R. At 1;000 ft. AGL the airplane was fully configured; on speed and before landing checklist completed. I continued the visual approach to a normal landing. Both the Captain and I could not figure out why this event occurred. What makes the glide slope to all of the sudden dive to the bottom of the display?? Either there was a system malfunction; or a truck or airplane drove or taxied across the ILS critical area. (Our assumption).
Data retrieved from NASA's ASRS site 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.