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With the autopilot engaged; crew intercepted the localizer and glideslope (GS) to 10L at ord. At approximately 2;700 MSL the aircraft pitched nose down. The autopilot did not correct the deviation and increased the downward pitch. As the downward pitch increased the captain disconnected the autopilot and corrected the pitch attitude to a stable flight path and landing. Crew suspects that there was ground aircraft interference with the ILS/GS transmitter signal.
| Attributes | |
| ACN | 1294627 |
| Time | |
| Date | 201509 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ORD.Airport |
| State Reference | IL |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B737-800 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Initial Approach |
| Flight Plan | IFR |
| Person 1 | |
| Function | Captain Pilot Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Person 2 | |
| Function | Pilot Not Flying First Officer |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Total 14000 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe |
Narrative:
Encountered a nose-low usual attitude while approaching ord at night under VFR conditions. Autopilot engaged; approach mode in use; gear down flaps 15 and speed 170 knots. GS and localizer captured. Altitude between 2;500 feet and 3;000 feet. The glide slope rapidly deflected to full scale and the autopilot and trim followed. I disconnected the autopilot and began recovery as nose-low guidance on the HUD became active. We may have approached 20 degrees nose down pitch. Max speed was 197 knots so we didn't over speed the flaps. After recovery and stabilized I continued the approach. We were stable at 1;000 feet so I did not go around. On landing we noticed a line of heavy aircraft on the south side of 10L. Normally aircraft wait on the north side. I suspect GS interference by the heavies. Fatigue was a factor since we flew the red eye in the morning. Spent daylight hours in the hotel and then on the same day flew a night flight. When using 10L as only runway during late night ops; aircraft should wait on the north side of 10L.
Original NASA ASRS Text
Title: With the autopilot engaged; crew intercepted the localizer and glideslope (GS) to 10L at ORD. At approximately 2;700 MSL the aircraft pitched nose down. The autopilot did not correct the deviation and increased the downward pitch. As the downward pitch increased the Captain disconnected the autopilot and corrected the pitch attitude to a stable flight path and landing. Crew suspects that there was ground aircraft interference with the ILS/GS transmitter signal.
Narrative: Encountered a nose-low usual attitude while approaching ORD at night under VFR conditions. Autopilot engaged; approach mode in use; gear down flaps 15 and speed 170 knots. GS and LOC captured. Altitude between 2;500 feet and 3;000 feet. The glide slope rapidly deflected to full scale and the autopilot and trim followed. I disconnected the autopilot and began recovery as nose-low guidance on the HUD became active. We may have approached 20 degrees nose down pitch. Max speed was 197 knots so we didn't over speed the flaps. After recovery and stabilized I continued the approach. We were stable at 1;000 feet so I did not go around. On landing we noticed a line of heavy aircraft on the south side of 10L. Normally aircraft wait on the north side. I suspect GS interference by the heavies. Fatigue was a factor since we flew the red eye in the morning. Spent daylight hours in the hotel and then on the same day flew a night flight. When using 10L as only runway during late night ops; aircraft should wait on the north side of 10L.
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.