Narrative:

I was pilot flying (PF); autopilot was engaged; weather was exceptionally clear and radio traffic was pretty light. I briefed the approach RNAV (rnp) Y runway 8 prior to descent. During the STAR; we were given a few altitude and airspeed restrictions and (maybe) a vector before being cleared direct to wabbt and cleared the RNAV (rnp) Y runway 8 into bur. After getting approach clearance; I went through my normal routine; pressed the VNAV button; and verbalized that I was setting 3;000 feet in the altitude window. I then proceeded to monitor the approach and spent a lot of time looking outside for traffic and looking for visual clues to find the runway. After passing wabbt; I checked for the next altitude crossing restriction (5;100 feet at nibyi) and noticed that we were still descending below that altitude. I also noticed the terrain (3;741 feet) would be a factor if we continued descending. After assessing the situation; I realized the autopilot was still in level change with 210 knots selected. I clicked off the autopilot and shallowed the descent rate to ensure terrain clearance and very shortly after; the socal controller advised us of our altitude deviation and then the low altitude alert. The pilot monitoring (pm) informed the controller that we had visual contact with the terrain and the runway and requested the visual approach. The rest of the flight was uneventful. We did not receive an egpws alert and; because we had visual contact with the terrain; we never felt terrain separation was a factor. I verbalized but we both did not verify and therefore we later had to intervene. I pushed the VNAV button but did not verify that VNAV path was engaged and that mistake led to our deviation. We could have (and should have) prevented this incident using better crew coordination and adhering to standard operating practices.

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Original NASA ASRS Text

Title: B737-700 flight crew reported descending below charted altitude on the RNAV (RNP) Y arrival to Runway 8 at BUR. Lack of FMC mode awareness was cited as contributing.

Narrative: I was Pilot Flying (PF); autopilot was engaged; weather was exceptionally clear and radio traffic was pretty light. I briefed the approach RNAV (RNP) Y Runway 8 prior to descent. During the STAR; we were given a few altitude and airspeed restrictions and (maybe) a vector before being cleared direct to WABBT and cleared the RNAV (RNP) Y Runway 8 into BUR. After getting approach clearance; I went through my normal routine; pressed the VNAV button; and verbalized that I was setting 3;000 feet in the altitude window. I then proceeded to monitor the approach and spent a lot of time looking outside for traffic and looking for visual clues to find the runway. After passing WABBT; I checked for the next altitude crossing restriction (5;100 feet at NIBYI) and noticed that we were still descending below that altitude. I also noticed the terrain (3;741 feet) would be a factor if we continued descending. After assessing the situation; I realized the autopilot was still in Level Change with 210 knots selected. I clicked off the autopilot and shallowed the descent rate to ensure terrain clearance and very shortly after; the SoCal Controller advised us of our altitude deviation and then the low altitude alert. The Pilot Monitoring (PM) informed the controller that we had visual contact with the terrain and the runway and requested the visual approach. The rest of the flight was uneventful. We did not receive an EGPWS alert and; because we had visual contact with the terrain; we never felt terrain separation was a factor. I verbalized but we both did NOT verify and therefore we later had to intervene. I pushed the VNAV button but did not verify that VNAV PATH was engaged and that mistake led to our deviation. We could have (and should have) prevented this incident using better crew coordination and adhering to standard operating practices.

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.