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B737 first officer reported deviating from altitude restrictions during descent to land.
| Attributes | |
| ACN | 1697902 |
| Time | |
| Date | 201911 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | CA |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | First Officer Pilot Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 459 Flight Crew Type 459 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy |
Narrative:
The aircraft had the autothrottle system MEL inoperative. Center assigned a speed of 300 kts or greater; and direct to zzzzz waypoint. Upon handoff to [approach]; we were then cleared the ILS xxr; and 2;200 feet was set in the MCP altitude window. At the deceleration point to slow to 270 kts; the aircraft pitch adjusted nose up; but not enough; and the aircraft descended below the VNAV path and the lower crossing restriction of 12;000 feet prior to reaching ZZZZZ1.VNAV disconnect occurred and the vertical mode reverted to cws (control wheel steering) pitch. The PF (pilot flying) intervened with vertical speed mode; and set 10;000 feet; in the altitude window for the next crossing restriction. Due to the autothrottles being inoperative; the thrust remained at idle the whole time; [there was] also negative turbulence during the descent. After passing ZZZZZ1 the VNAV path was re-joined with MCP VNAV mode; no further deviations during the descent. I was more focused on the magenta descent path deviation and the VNAV disconnect rather than the actual aircraft altitude; which caused me to be slow to react. Also I would like to add that other than the 300 kt speed assignment; there was nothing unusual and the autopilot should not have missed that altitude.
Original NASA ASRS Text
Title: B737 First Officer reported deviating from altitude restrictions during descent to land.
Narrative: The aircraft had the Autothrottle System MEL inoperative. Center assigned a speed of 300 kts or greater; and direct to ZZZZZ waypoint. Upon handoff to [Approach]; we were then cleared the ILS XXR; and 2;200 feet was set in the MCP Altitude window. At the deceleration point to slow to 270 kts; the aircraft pitch adjusted nose up; but not enough; and the aircraft descended below the VNAV PATH and the lower crossing restriction of 12;000 feet prior to reaching ZZZZZ1.VNAV disconnect occurred and the Vertical mode reverted to CWS (Control Wheel Steering) pitch. The PF (Pilot Flying) intervened with Vertical Speed mode; and set 10;000 feet; in the altitude window for the next crossing restriction. Due to the autothrottles being inoperative; the thrust remained at idle the whole time; [there was] also negative turbulence during the descent. After passing ZZZZZ1 the VNAV PATH was re-joined with MCP VNAV mode; no further deviations during the descent. I was more focused on the magenta descent path deviation and the VNAV disconnect rather than the actual aircraft altitude; which caused me to be slow to react. Also I would like to add that other than the 300 kt speed assignment; there was nothing unusual and the autopilot should not have missed that altitude.
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.