Narrative:

We were on a flight to bur; on descent on the janny 5 arrival into bur. At some point near janny intersection we were cleared to descend to 6;000 feet. Since this clearance was understood to be a 'descend to' (now) not 'descend via;' I commanded a new non-VNAV mode which we had been using. I believe the new mode was level change/vertical descent in FPM. It was not a VNAV descent mode. I verbalized this change. Shortly afterward; the approach controller asked if we would prefer the ILS or the RNAV Y to runway 8 in bur. We requested the RNAV Y runway 8. He then cleared us for this approach; direct wabbt. RNAV Y links up with janny 5 at wabbt intersection and we were cleared to this intersection. We selected wabbt direct; closed the discontinuity; reviewed weski as the fap [final approach point] with a corresponding 2;700 feet altitude; agreed and set that altitude into the MCP window. At that point I believe I made an error by not verifying and verbalizing VNAV path as the vertical mode. This set up the aircraft to continue a moderate rate; non-idle; descent on autopilot toward 2;700 feet. At about 4;900 feet and approaching wabbt; a GPWS caution obstacle alert was heard. I immediately disengaged the autopilot and the autothrottles and pitched aircraft into a climb. Shortly afterwards; approach control asked us to verify altitude. We responded we were climbing to 6;000 feet. After wabbt; RNAV 8 approach then started a series of stepdown altitudes and arc left turns. I asked my first officer [first officer] for the next altitude so I could safely begin to descend again. He interpreted this as a verbal altitude whereas I wanted an MCP altitude window setting. I also commanded a direct enter toward the zemep intersection but inadvertently forgot the autopilot was disengaged and would not execute the turn automatically so we briefly overflew this intersection before turning back on course to re-intercept the approach. We re-established the approach; configured; then flew the approach to runway 8 which became visually in sight several miles out. We were handed off to tower and made a normal landing at bur. When we were cleared to 6;000 feet I should have chosen a VNAV mode rather than assuming I would be pulled off further STAR/approach restrictions for the remainder of the flight. I had an expectation bias that we would be receiving vectors but were re-cleared on a procedure that required VNAV. More importantly; I should have verbalized and verified VNAV path on procedure requiring its use. This was missed as we turned the discussion to the minimum altitude to set in the MCP window. Lastly; on any segment of the approach a missed approach should have been called and executed even when a long way from the MDA/dda point of the approach.

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Original NASA ASRS Text

Title: B737 flight crew received a Ground Proximity Warning System Alert while on descent to destination airport.

Narrative: We were on a flight to BUR; on descent on the JANNY 5 Arrival into BUR. At some point near JANNY intersection we were cleared to descend to 6;000 feet. Since this clearance was understood to be a 'descend to' (now) not 'descend via;' I commanded a new non-VNAV mode which we had been using. I believe the new mode was Level Change/Vertical Descent in FPM. It was not a VNAV descent mode. I verbalized this change. Shortly afterward; the Approach Controller asked if we would prefer the ILS or the RNAV Y to Runway 8 in BUR. We requested the RNAV Y Runway 8. He then cleared us for this approach; direct WABBT. RNAV Y links up with JANNY 5 at WABBT Intersection and we were cleared to this intersection. We selected WABBT direct; closed the discontinuity; reviewed WESKI as the FAP [Final Approach Point] with a corresponding 2;700 feet altitude; agreed and set that altitude into the MCP window. At that point I believe I made an error by not verifying and verbalizing VNAV PATH as the vertical mode. This set up the aircraft to continue a moderate rate; non-idle; descent on autopilot toward 2;700 feet. At about 4;900 feet and approaching WABBT; a GPWS Caution Obstacle Alert was heard. I immediately disengaged the autopilot and the autothrottles and pitched aircraft into a climb. Shortly afterwards; Approach Control asked us to verify altitude. We responded we were climbing to 6;000 feet. After WABBT; RNAV 8 Approach then started a series of stepdown altitudes and arc left turns. I asked my F/O [First Officer] for the next altitude so I could safely begin to descend again. He interpreted this as a verbal altitude whereas I wanted an MCP altitude window setting. I also commanded a direct enter toward the ZEMEP intersection but inadvertently forgot the autopilot was disengaged and would not execute the turn automatically so we briefly overflew this intersection before turning back on course to re-intercept the approach. We re-established the approach; configured; then flew the approach to Runway 8 which became visually in sight several miles out. We were handed off to Tower and made a normal landing at BUR. When we were cleared to 6;000 feet I should have chosen a VNAV mode rather than assuming I would be pulled off further STAR/approach restrictions for the remainder of the flight. I had an expectation bias that we would be receiving vectors but were re-cleared on a procedure that required VNAV. More importantly; I should have verbalized and verified VNAV PATH on procedure requiring its use. This was missed as we turned the discussion to the minimum altitude to set in the MCP window. Lastly; on any segment of the approach a missed approach should have been called and executed even when a long way from the MDA/DDA point of the approach.

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.