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A B757-200 captain reported that at 500' after takeoff with LNAV and VNAV selected the autopilot was selected on. At 1;800' the aircraft pitched down requiring an autopilot disconnect and both pilots pulling to stop the descent at 1;100' and begin a climb. A faulty autopilot trim was suspected as the cause of the event.
| Attributes | |
| ACN | 877049 |
| Time | |
| Date | 201003 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B757-200 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Initial Climb |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Autopilot |
| Person 1 | |
| Function | Captain Pilot Not Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Deviation - Altitude Undershoot Inflight Event / Encounter Loss Of Aircraft Control |
Narrative:
After deicing; we took off in blowing snow with the first officer flying. At 4000 ft; LNAV was selected. At 500 ft; the right autopilot was engaged. At 1000 ft; VNAV was selected. At about 1800 ft; an amber 'autopilot' message illuminated on the EICAS; and the aircraft pitched nose down. The first officer disconnected the autopilot and began pulling up. The nose was so heavy that he initially thought that the trim was running away. I also began pulling up; and the nose felt so heavy that I initially though that the first officer was pushing against me. Our recovery bottomed out at about 1100 ft with the GPWS yelling at us. I believe that for some reason the autopilot trimmed the aircraft excessively nose down. We continued to our planned destination using another autopilot.
Original NASA ASRS Text
Title: A B757-200 Captain reported that at 500' after takeoff with LNAV and VNAV selected the autopilot was selected ON. At 1;800' the aircraft pitched down requiring an autopilot disconnect and both pilots pulling to stop the descent at 1;100' and begin a climb. A faulty autopilot trim was suspected as the cause of the event.
Narrative: After deicing; we took off in blowing snow with the First Officer flying. At 4000 FT; LNAV was selected. At 500 FT; the right autopilot was engaged. At 1000 FT; VNAV was selected. At about 1800 FT; an amber 'AUTOPILOT' message illuminated on the EICAS; and the aircraft pitched nose down. The First Officer disconnected the autopilot and began pulling up. The nose was so heavy that he initially thought that the trim was running away. I also began pulling up; and the nose felt so heavy that I initially though that the First Officer was pushing against me. Our recovery bottomed out at about 1100 FT with the GPWS yelling at us. I believe that for some reason the autopilot trimmed the aircraft excessively nose down. We continued to our planned destination using another autopilot.
Data retrieved from NASA's ASRS site as of April 2012 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.