B737NG flight crew reported neglecting to select VNAV resulting in a descent below the arrival profi...

Attributes
ACN	1439984
Time
Date	201704
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 175
Person 2
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 209 Flight Crew Type 4268
Events
Anomaly	Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

While descending into ZZZ; we were following another aircraft. We were slowed first; then vectored off course to create spacing. After there was enough spacing; we were cleared back onto the arrival and to descend via. I put the fix in the box and selected LNAV. I rolled in our new altitude but forgot to select VNAV (level change was still selected). We continued to descend to our altitude via level change and went below the arrival altitudes. We entered clouds and when we got out of the bottom we both noticed we were low. As we tried to call ATC; they called us and we climbed to 5100 feet MSL. No alerts went off.the distraction was clouds/turbulence approaching. We were discussing our plan to coordinate with the flight attendants to clean the cabin and sit before the turbulence hit. We were issued our clearance during a time when we were also talking to the flight attendants. I entered our clearance but we failed to verify that VNAV was selected. It was error on both pilot flying and monitoring. We were more concerned with flight attendant safety at that exact moment than verifying our automation.

Original NASA ASRS Text

Title: B737NG flight crew reported neglecting to select VNAV resulting in a descent below the arrival profile.

Narrative: While descending into ZZZ; we were following another aircraft. We were slowed first; then vectored off course to create spacing. After there was enough spacing; we were cleared back onto the Arrival and to descend via. I put the fix in the box and selected LNAV. I rolled in our new altitude but forgot to select VNAV (Level Change was still selected). We continued to descend to our altitude via Level Change and went below the arrival altitudes. We entered clouds and when we got out of the bottom we both noticed we were low. As we tried to call ATC; they called us and we climbed to 5100 feet MSL. No alerts went off.The distraction was clouds/turbulence approaching. We were discussing our plan to coordinate with the Flight Attendants to clean the cabin and sit before the turbulence hit. We were issued our clearance during a time when we were also talking to the Flight Attendants. I entered our clearance but we failed to verify that VNAV was selected. It was error on both Pilot Flying and Monitoring. We were more concerned with Flight Attendant safety at that exact moment than verifying our automation.

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.