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B737 captain reported that in 2 different aircraft at this location; the aircraft did not follow the programmed VNAV flight path.
| Attributes | |
| ACN | 1711681 |
| Time | |
| Date | 201912 |
| Local Time Of Day | 0001-0600 |
| Place | |
| Locale Reference | NCT.TRACON |
| State Reference | CA |
| Environment | |
| Flight Conditions | VMC |
| Aircraft 1 | |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Route In Use | Direct |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Flight Dynamics Navigation and Safety |
| Person 1 | |
| Function | Pilot Flying Captain |
| Qualification | Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 163 Flight Crew Total 2903 Flight Crew Type 2903 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude |
Narrative:
For the second time in a month; in two different aircraft; I have had the same issue with VNAV busting an altitude constraint at the same fix. Inbound to sfo on the PIRAT2 arrival. Clearance is to cross arggg at 8;000 ft.; then maintain 4;000 ft. In VNAV path with 8;000 ft. Programmed at arggg and 4;000 ft. Set in the MCP window. All is normal until a couple of miles prior to arggg when the VNAV pdi pops to full scale high and the aircraft chases the path and ignores the constraint. I disconnected the autopilot at 7;800 ft. And popped back up to 8;000 ft. Until crossing the fix. Same thing on both occurrences. This will bite someone as it is the end of a red eye crossing from hawaii.
Original NASA ASRS Text
Title: B737 Captain reported that in 2 different aircraft at this location; the aircraft did not follow the programmed VNAV flight path.
Narrative: For the second time in a month; in two different aircraft; I have had the same issue with VNAV busting an altitude constraint at the same fix. Inbound to SFO on the PIRAT2 arrival. Clearance is to cross ARGGG at 8;000 ft.; then maintain 4;000 ft. In VNAV path with 8;000 ft. programmed at ARGGG and 4;000 ft. set in the MCP window. All is normal until a couple of miles prior to ARGGG when the VNAV PDI pops to full scale high and the aircraft chases the path and ignores the constraint. I disconnected the autopilot at 7;800 ft. and popped back up to 8;000 ft. until crossing the fix. Same thing on both occurrences. This will bite someone as it is the end of a red eye crossing from Hawaii.
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.