Date: 201310
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Flap/Slat Control System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Communication Breakdown; Confusion
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Terrain Warning; Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Procedure; Weather; Environment - Non Weather Related
Primary problem: Ambiguous

Narrative: Briefed a Flaps 30 approach and landing Runway 35R. Due to gusty winds planned for a ref of 145 and a target speed of 160 KTS. ATC vectored us off of the arrival and had us parallel the course with a heading and descent while pointing out multiple traffic eastbound to intercept final for 35L. Twice Approach Control gave us direct points on published ILS for us to join for the visual approach to Runway 35R requiring changes to the FMC. Normal configuration was commanded along with the landing checklist. At approximately 6;500 FT while hand flying the airplane I called for Flaps 30 and target speed. All was normal until about 400 FT when we received a GPWS alert for 'too low terrain.' I double checked the gear was down; speed was target plus about 5 which was roughly 165 KTS. I then noticed that the flaps were still set at 15 degrees. Due to our higher than normal target speed we were well above the yellow band on the airspeed indicator; pitch was not abnormally high. I added about another 5 KTS and landed the aircraft.


Second narrative: On approach maintained good sterile cockpit compliance. Cleared for visual approach to 35R and maintain 170 to outer marker. Gear was put out 5-10 miles from outer marker. Which left us flying in the gear down Flaps 15 configuration for a few minutes. Some traffic was called out to us by the Approach Controller that was eastbound; which both of noted was a different traffic call as we were northbound for 35R. Approach speed was initially set for 160 KTS.I never heard the Captain call for Flaps 30. I was distracted by a few things on approach; trying to listen to the wind read outs from Tower; looking out for that traffic call; and I remember trying to remember if the airplane made a 2;500 foot call.I believe we adjusted the ref speed to plus 10 due to the Tower wind read outs. I also remember trying to really focus in on the new altitude tape trying to do the mental math on the altitude call outs and all of the new details the flight display were giving.At about 400 FT the GPWS started calling out too low terrain. We were VMC on glide path. I thought that the GPWS was malfunctioning. I believe the Captain thought the same thing as he asked if I could turn that off. I selected the terrain mode off. At about 200 FT while discussing that with the Captain; I think it said too low flaps. Still thinking it was malfunctioning; I started to look at our configuration and stated that we have 3 green lights meaning the gear was down. About 50-100 FT the Captain states that we only have Flaps 15. We landed without incident. I did not notice us having a weird deck angle; it all looked normal from a non flying position.


Synopsis: A distracted B737 crew landed with Flaps 15 in gusty winds as the GPWS TOO LOW TERRAIN warning alerted at 400 FT after a task saturated the First Officer failed to hear the Captain's Flaps 30 request.