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Boeing 737-700 flight crew reported an autopilot anomaly that caused the aircraft to deviate off final approach course.
| Attributes | |
| ACN | 1511962 |
| Time | |
| Date | 201801 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Initial Approach |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Autopilot |
| Person 1 | |
| Function | Pilot Flying First Officer |
| Qualification | Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 389 Flight Crew Type 2600 |
| Person 2 | |
| Function | Pilot Not Flying Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 360 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Track / Heading All Types |
Narrative:
I was the pilot flying and configured with flaps 30 on the RNAV Z runway xxl. The aircraft was within five knots of planned speed and stable on final. The before landing checklist was complete. LNAV and VNAV were engaged; we were in VNAV path and the altitude window was in 0000. On the map depiction I was on a 10 mile range and the aircraft appeared to be on the magenta line. For no apparent reason; the aircraft started rolling to the right. At first I thought it was due to the slight crosswind; but it continued to roll right. Both the captain and I voiced our concern; and approaching 20 degrees of right roll (and continuing right roll); I disengaged the autopilot and manually corrected to final approach using the ILS guidance. Maximum right deviation on the ILS/localizer was approximately one dot and we were VFR the entire sequence. Roll rate was not abrupt; but rather a normal commanded roll rate by the automation. Landing was uneventful. After landing both the captain and I tried to figure out why the roll occurred; but could not come up with any plausible explanation.
Original NASA ASRS Text
Title: Boeing 737-700 flight crew reported an autopilot anomaly that caused the aircraft to deviate off final approach course.
Narrative: I was the pilot flying and configured with flaps 30 on the RNAV Z Runway XXL. The aircraft was within five knots of planned speed and stable on final. The Before Landing Checklist was complete. LNAV and VNAV were engaged; we were in VNAV PATH and the altitude window was in 0000. On the map depiction I was on a 10 mile range and the aircraft appeared to be on the magenta line. For no apparent reason; the aircraft started rolling to the right. At first I thought it was due to the slight crosswind; but it continued to roll right. Both the Captain and I voiced our concern; and approaching 20 degrees of right roll (and continuing right roll); I disengaged the autopilot and manually corrected to final approach using the ILS guidance. Maximum right deviation on the ILS/LOC was approximately one dot and we were VFR the entire sequence. Roll rate was not abrupt; but rather a normal commanded roll rate by the automation. Landing was uneventful. After landing both the Captain and I tried to figure out why the roll occurred; but could not come up with any plausible explanation.
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.