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B737-800 captain reported recovering from an autopilot malfunction that put the aircraft into an uncommanded 70 degree bank and resulted in an altitude loss of 500 ft.
| Attributes | |
| ACN | 1436233 |
| Time | |
| Date | 201703 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-800 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Autopilot |
| Person 1 | |
| Function | Captain Pilot Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Events | |
| Anomaly | Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Loss Of Aircraft Control |
Narrative:
At FL260 and 310 knots assigned airspeed; the aircraft executed an uncommanded roll. The first officer and I had just been discussing the possibility of an arrival change; due to the landing configuration at destination and were referencing our ipads in anticipation of the change. When I returned my attention to the instruments the aircraft was rolling through 60 degrees of bank. It took a few moments to process what the aircraft was doing. At approximately 70 degrees of bank I disconnected the #1 autopilot and initiated a recovery. Approximately 500 feet of altitude was lost during the recovery. With control of the aircraft reestablished; we notified ATC of the deviation. ATC then directed us to descend to FL240. Although noticeable to the passengers and cabin crew; the seatbelt sign was on and no injuries were reported. The remainder of the flight was unremarkable. After landing; I entered the anomaly in the logbook and spoke with maintenance before leaving the aircraft. I am still puzzled as to the cause of roll; but I am grateful for the unusual attitude recovery training we practice at recurrent.
Original NASA ASRS Text
Title: B737-800 Captain reported recovering from an autopilot malfunction that put the aircraft into an uncommanded 70 degree bank and resulted in an altitude loss of 500 ft.
Narrative: At FL260 and 310 knots assigned airspeed; the aircraft executed an uncommanded roll. The FO and I had just been discussing the possibility of an arrival change; due to the landing configuration at destination and were referencing our iPads in anticipation of the change. When I returned my attention to the instruments the aircraft was rolling through 60 degrees of bank. It took a few moments to process what the aircraft was doing. At approximately 70 degrees of bank I disconnected the #1 autopilot and initiated a recovery. Approximately 500 feet of altitude was lost during the recovery. With control of the aircraft reestablished; we notified ATC of the deviation. ATC then directed us to descend to FL240. Although noticeable to the passengers and cabin crew; the seatbelt sign was on and no injuries were reported. The remainder of the flight was unremarkable. After landing; I entered the anomaly in the logbook and spoke with Maintenance before leaving the aircraft. I am still puzzled as to the cause of roll; but I am grateful for the unusual attitude recovery training we practice at recurrent.
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.