Narrative:

We unintentionally landed with flaps 15 rather than the planned and briefed flaps 30. Multiple factors contributed to unrecognized task saturation on final approach. ATIS advertised runway 26 and 35C and 35R. We briefed runway 26 with a backup of 35R. ATIS winds were 290/23g39. We briefed a vref of 144 and a target of 164. We completed the approach decent checklist well before the top of decent. We were cleared to descend via kohoe 3 arrival except maintain 300kts. Later in the decent we were told to slow to 250 and comply with speed restrictions. This made it impossible to make one of the at or below altitudes. We asked for altitude relief and were given a descend and maintain 13;000 and were told to expect runway 35R. All of this increased our workload but was well managed. We did not feel behind the aircraft. We were given a normal base and downwind leg. Then we were given a heading for a dogleg to intercept 35R and cleared for the visual on that heading.several other factors caused us to unknowingly become task saturated. First; the first officer accidentally extended the runway instead of the final approach fix and was working to correct the error as we were on dogleg. Second; due to strong crosswinds the ground track of the assigned heading put us inside the final approach fix. I called for gear down; flaps 15; landing checklist; and set target speed at approximately 1;600 afe. Approach was armed and we were on glide path but we were right of the localizer course due to the assigned heading and strong crosswind. I didn't understand why the glide path was not capturing and verbalized this. The first officer reminded me that the glideslope will not capture prior to the localizer capturing. At this point I flew through the flight directors to maintain the glideslope until localizer capture. The first officer made the 1000-foot call; set missed approach altitude; and I confirmed landing clearance. Winds were steady; approximately 270/25; and airspeed was stable. The first officer made the 500-foot call and all seemed stabilized. We were on glide path; on localizer; and on airspeed. At approximately 200 feet I was about dot low on the glideslope with 1 white and 3 red on the PAPI when we received the GPWS 'too low terrain.' I didn't understand why and thought it was because I was low on the glideslope. I corrected to on glide slope but the warning continued. I confirmed the gear was down. I thought maybe we had put the wrong runway in the FMC. Everything seemed stable and normal; so I continued to a landing; which was uneventful. The aircraft floated a bit but I assumed that was due to the 20 kts of extra airspeed. It was not until the after landing flow that the first officer noticed the flaps were at 15 instead of 30.the first officer and I debriefed extensively flowing the flight and agreed task saturation was the primary cause. I had not called for final flaps; and the first officer had not completed the flap portion of the landing checklist.in hindsight it is clear I should have gone around when I could not immediately determine why we were getting the GPWS 'too low terrain' warning. This is the number one lesson for me. The second lesson is once we were cleared for the visual approach and I felt comfortable with the approach I should have turned off the automation and continued visually. At that point the automation became a significant distraction as we worked to get it caught up with where we were on the approach. Had we not been distracted with the automation; I believe both the first officer and I would have caught the flaps setting during the landing checklist.

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Original NASA ASRS Text

Title: B737 Captain reported that because of workload and distractions they landed with flaps 15 instead of the briefed and planned flaps 30.

Narrative: We unintentionally landed with flaps 15 rather than the planned and briefed flaps 30. Multiple factors contributed to unrecognized task saturation on final approach. ATIS advertised runway 26 and 35C and 35R. We briefed runway 26 with a backup of 35R. ATIS winds were 290/23G39. We briefed a Vref of 144 and a target of 164. We completed the Approach Decent checklist well before the top of decent. We were cleared to descend via Kohoe 3 arrival except maintain 300kts. Later in the decent we were told to slow to 250 and comply with speed restrictions. This made it impossible to make one of the at or below altitudes. We asked for altitude relief and were given a descend and maintain 13;000 and were told to expect runway 35R. All of this increased our workload but was well managed. We did not feel behind the aircraft. We were given a normal base and downwind leg. Then we were given a heading for a dogleg to intercept 35R and cleared for the visual on that heading.Several other factors caused us to unknowingly become task saturated. First; the FO accidentally extended the runway instead of the final approach fix and was working to correct the error as we were on dogleg. Second; due to strong crosswinds the ground track of the assigned heading put us inside the final approach fix. I called for gear down; flaps 15; landing checklist; and set target speed at approximately 1;600 AFE. Approach was armed and we were on glide path but we were right of the localizer course due to the assigned heading and strong crosswind. I didn't understand why the glide path was not capturing and verbalized this. The FO reminded me that the glideslope will not capture prior to the localizer capturing. At this point I flew through the flight directors to maintain the glideslope until localizer capture. The FO made the 1000-foot call; set missed approach altitude; and I confirmed landing clearance. Winds were steady; approximately 270/25; and airspeed was stable. The FO made the 500-foot call and all seemed stabilized. We were on glide path; on localizer; and on airspeed. At approximately 200 feet I was about dot low on the glideslope with 1 white and 3 red on the PAPI when we received the GPWS 'TOO LOW TERRAIN.' I didn't understand why and thought it was because I was low on the glideslope. I corrected to on glide slope but the warning continued. I confirmed the gear was down. I thought maybe we had put the wrong runway in the FMC. Everything seemed stable and normal; so I continued to a landing; which was uneventful. The aircraft floated a bit but I assumed that was due to the 20 kts of extra airspeed. It was not until the after landing flow that the FO noticed the flaps were at 15 instead of 30.The FO and I debriefed extensively flowing the flight and agreed task saturation was the primary cause. I had not called for final flaps; and the FO had not completed the flap portion of the landing checklist.In hindsight it is clear I should have gone around when I could not immediately determine why we were getting the GPWS 'TOO LOW TERRAIN' warning. This is the number one lesson for me. The second lesson is once we were cleared for the visual approach and I felt comfortable with the approach I should have turned off the automation and continued visually. At that point the automation became a significant distraction as we worked to get it caught up with where we were on the approach. Had we not been distracted with the automation; I believe both the FO and I would have caught the flaps setting during the landing checklist.

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.