B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 460
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation
Human Factors
It was an unremarkable sortie in VMC conditions. Due to a report of moderate turbulence during the descent of a preceding aircraft; I directed early cabin cleanup and asked the Flight Attendants to take their seats before coast in. Spacing requirements dictated slower than normal speeds and nothing else was out of the ordinary. Once obtaining a visual on a regional jet in front of us; we were advised that we should maintain 170 Knots and were cleared for the Visual Approach. On Tower frequency; we were advised to slow to final approach speed (we were almost there already). I directed the final flap setting and a Before Landing Checklist. The flap settings before directing that final checklist had been flaps 1; then flaps 2; flaps 5; flaps 15 (after directing gear down). A very standard visual profile. I did not direct flaps 25 at any time.As the regional jet in front of us cleared the runway; the final approach segment of the visual commenced. Spacing with the regional was not an issue. We completed the Before Landing Checklist and prepared for landing when we heard the aural 'too low flaps' annunciation. Instinctively I looked at the center pedestal and found that the flap handle was between the 25 and 30 detents. I moved the lever into the 30 detent and then continued the visual final to landing. There were no external threats beside complacency and a familiarity between Pilots (we have been paired together all month). Spacing and directed speeds were not an issue; and when directed to slow to final airspeed; we were nearly there and were not rushed. I was really disappointed in the lip service we obviously exhibited with regards to the Before Landing Checklist. There was an expectation bias at work there also; as '30 flaps' had been directed and the First Officer had thought he had complied. I like to think that I dwell on each item of that checklist; but we both missed the inappropriate flap setting before the aural annunciation.
B737-700 Captain reported an improper flap setting on approach which caused the Terrain Alert to activate.