B737-700 flight crew reported descending below charted altitude on approach when the pilot not flyin...

Attributes
ACN	1226509
Time
Date	201412
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Person 1
Function	Pilot Not Flying Captain
Experience	Flight Crew Last 90 Days 178 Flight Crew Type 10000
Person 2
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 152 Flight Crew Type 5800
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

Cleared initially 31R into ZZZ when changed frequency and changed approach runway to 31L. First officer set 1200 ft in altitude and verbalized; but I did not catch because I was verifying frequency and altitude changes from new runway assignment. First officer stated we looked low and started to climb. At 1800 ft I looked up at altitude window and stated we want 2200 ft not 1200 ft and simultaneously; ATC told us to climb. We were visual with the field and buildings climbed to 2200 ft and intercepted the glideslope and continued uneventfully on a normal approach and landing. [I should] verify any change on MCP with pilot flying before [going] heads down to make changes or don't make the change.

Original NASA ASRS Text

Title: B737-700 flight crew reported descending below charted altitude on approach when the pilot not flying failed to verify MCP altitude change.

Narrative: Cleared initially 31R into ZZZ when changed frequency and changed approach Runway to 31L. FO set 1200 FT in altitude and verbalized; but I did not catch because I was verifying frequency and altitude changes from new runway assignment. FO stated we looked low and started to climb. At 1800 FT I looked up at altitude window and stated we want 2200 FT not 1200 FT and simultaneously; ATC told us to climb. We were visual with the field and buildings climbed to 2200 FT and intercepted the glideslope and continued uneventfully on a normal approach and landing. [I should] verify any change on MCP with Pilot Flying before [going] heads down to make changes or don't make the change.

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.