<< >> NASA ASRS Report 1711681, December 2019

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.

Related reports:

• Air carrier flight does not follow flight plan as filed with...

	Enter your search terms Submit search form
	Web www.37000feet.com

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.