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The flight crew reported that; during a critical phase of their approach; the ILS glideslope signal was disturbed by an aircraft taxiing down the runway. The autopilot was quickly disengaged; however the aircraft momentarily descended below the glidescope; generating a terrain proximity warning from the control tower. A timely correction was made and the approach and landing were completed successfully.
| Attributes | |
| ACN | 1286770 |
| Time | |
| Date | 201507 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | CLT.Airport |
| State Reference | NC |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Bombardier/Canadair Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Initial Approach |
| Flight Plan | IFR |
| Person 1 | |
| Function | Pilot Not Flying Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Events | |
| Anomaly | ATC Issue All Types Aircraft Equipment Problem Less Severe Inflight Event / Encounter CFTT / CFIT Inflight Event / Encounter Unstabilized Approach |
Narrative:
During our approach to runway clt 36R; [a flight] (#unknown) informed the tower that they would need to return to the gate. For whatever reason (taxiway construction? And aircraft awaiting takeoff on the east side of the runway); the tower chose to taxi the aircraft from the approach end of 36R to an exit taxiway farther down the runway to rejoin C taxiway.by doing this; our glideslope signal was disturbed causing the avionic flight control system (afcs) to pitch up to follow the distorted glideslope signal causing a sudden upset during final flap extension. The aircraft was stable; configured properly and the afcs was engaged and properly tracking the localizer and glideslope prior to this disturbance. Noticing the rapid decrease in airspeed; the afcs was disengaged; pitch reduced and thrust increased to stabilize the aircraft. Because of the rapid change in pitch attitude; the aircraft descended below the glideslope while regaining airspeed. This resulted in a low altitude warning from the tower. By this time; the aircraft was in visual conditions; the runway and the vertical glideslope indicator (vgsi) were in sight and we were in a position to continue a stable visual approach to landing.the aircraft behind us on the approach also complained of ILS disturbance during this same event.
Original NASA ASRS Text
Title: The flight crew reported that; during a critical phase of their approach; the ILS glideslope signal was disturbed by an aircraft taxiing down the runway. The autopilot was quickly disengaged; however the aircraft momentarily descended below the glidescope; generating a terrain proximity warning from the control Tower. A timely correction was made and the approach and landing were completed successfully.
Narrative: During our approach to runway CLT 36R; [a flight] (#unknown) informed the tower that they would need to return to the gate. For whatever reason (taxiway construction? and aircraft awaiting takeoff on the east side of the runway); the tower chose to taxi the aircraft from the approach end of 36R to an exit taxiway farther down the runway to rejoin C taxiway.By doing this; our glideslope signal was disturbed causing the Avionic Flight Control System (AFCS) to pitch up to follow the distorted glideslope signal causing a sudden upset during final flap extension. The aircraft was stable; configured properly and the AFCS was engaged and properly tracking the localizer and glideslope prior to this disturbance. Noticing the rapid decrease in airspeed; the AFCS was disengaged; pitch reduced and thrust increased to stabilize the aircraft. Because of the rapid change in pitch attitude; the aircraft descended below the glideslope while regaining airspeed. This resulted in a low altitude warning from the tower. By this time; the aircraft was in visual conditions; the runway and the Vertical Glideslope Indicator (VGSI) were in sight and we were in a position to continue a stable visual approach to landing.The aircraft behind us on the approach also complained of ILS disturbance during this same event.
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.