B757-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Wake Vortex Encounter
General None Reported / Taken
Aircraft; Environment - Non Weather Related; Procedure
We were cleared for the visual approach to Runway 17C using the ILS 17C as back-up. ATC cleared a 737 to join the final in front of us with approx 4 NM separation and asked us to maintain 180 knots to 5 NM final. We declined that instruction and told Approach that we could maintain 170 to 5 NM final (based on ability to slow and our perception that we were overtaking the traffic in front of us). ATC modified their instructions. Configuration at 5 NM was 170 KTS; Flaps 20; gear up - on glideslope; autopilot and autothrottles engaged. At about 5 NM/2;000 FT AGL; Captain asked for gear down to begin to slow. As the gear extended we encountered wake turbulence from the 737 4 NM in front of us resulting in a sharp roll to the right (about 20 degrees). Captain disconnected the autopilot and autothrottles; leveled the wings and asked for Flaps 25 (now about 1;800 FT AGL). Speed was approx 160-165 knots with some speed deviation (+ or - 5 knots) due to thermal activity.When I selected Flaps 25; we immediately received a TE FLAP DISAGREE EICAS message and saw the TE FLAPS caution light illuminated. Our first response was to verify that the flap handle was actually in the 25 detent - it was. The flap position indicator indicated 20 degrees. Our first instinct was to initiate a go-around; but very quickly changed our mind and decided that the safest course of action was to simply land in our current configuration. Captain stated his opinion that we should simply land; and I concurred with that decision. I provided Captain with a Flaps 20 reference speed and he adjusted his speed accordingly and we landed without further incident. Touchdown and rollout were normal and we left the flaps and flap handle where they were (parked with flaps extended and gave the airplane to Maintenance in that configuration).
[Narrative 2 had no additional information]
B757 flight crew reported wake vortex encounter from preceding B737 on approach to DFW resulting in a sharp roll.