B737-800 flight crew reported descending too low on approach to ric airport.

Attributes
ACN	1693417
Time
Date	201910
Local Time Of Day	1201-1800
Place
Locale Reference	RIC.Airport
State Reference	VA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

Narrative:

We were cleared for a visual approach runway 34. Weather clear. The first officer (first officer) was flying with the aircraft on autopilot B. He set the altitude alert for 1;700 feet and began descending to that altitude from 2;000 feet. We were not aligned with the runway. He also selected full approach mode. The aircraft caught the glide slope and began to descend. Again; we were not lined up with the runway yet. At some point; the glide slope fluctuated; which made the autopilot kick off. Simultaneously; ATC called a low altitude warning for us. This was at approximately 1;300 feet. First officer corrected and began to climb back up to 1;700 feet and re caught the glideslope. We landed without further incident.the 'gotcha' point was selecting the full approach mode instead of selecting localizer first and letting the airplane capture that then selecting the full approach when the glide slope was lined up. I should have monitored the situation better. It was clear with perfect weather and the airport was clearly in sight. I was looking outside instead of inside. Maintain a cross check inside and outside.

Original NASA ASRS Text

Title: B737-800 flight crew reported descending too low on approach to RIC airport.

Narrative: We were cleared for a visual approach Runway 34. Weather clear. The FO (First Officer) was flying with the aircraft on autopilot B. He set the altitude alert for 1;700 feet and began descending to that altitude from 2;000 feet. We were not aligned with the runway. He also selected full approach mode. The aircraft caught the glide slope and began to descend. Again; we were not lined up with the runway yet. At some point; the glide slope fluctuated; which made the autopilot kick off. Simultaneously; ATC called a low altitude warning for us. This was at approximately 1;300 feet. FO Corrected and began to climb back up to 1;700 feet and re caught the glideslope. We landed without further incident.The 'gotcha' point was selecting the full approach mode instead of selecting LOC first and letting the airplane capture that then selecting the full approach when the glide slope was lined up. I should have monitored the situation better. It was clear with perfect weather and the airport was clearly in sight. I was looking outside instead of inside. Maintain a cross check inside and outside.

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.