B737-700
Flight Crew Last 90 Days 123; Flight Crew Type 2500
Workload; Distraction
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Environment - Non Weather Related
250 KIAS speed restriction on SID. [We] briefed on ground during departure briefing. [We] used Level Change 250 on MCP until 11;000 FT MSL to avoid VNAV exceeding 250-KT restriction. [We] encountered wake turbulence from preceding aircraft while on departure climb vectors from Center around 10;000 FT MSL. On climb from 11;000 FT to 12;000 FT announced and selected VNAV; which accelerated climb speed to 270 KIAS. A few minutes later; ATC asked if we were at 250 KTS. We replied; 'Slowing.' TCAS distance from the preceding aircraft was in excess of five miles and the Controller never mentioned a possible deviation. We were assigned FL230 and normal speed leaving 14;000 FT.I simply forgot the speed restriction since it had been so long before that we briefed it due to ground congestion leading to departure delays. Additionally; numerous altitude assignments; heading changes; and frequency changes departing MDW made for a very busy departure. Furthermore; we encountered wake turbulence around 10;000 FT MSL; which added another threat to the departure. I announced the change of speed profile (VNAV); but the pilot not flying didn't challenge my mistake. It might be prudent in the future to change the Econ VNAV speed to the SID assignment of 250 KIAS in case the assignment is forgotten. Also; it would be helpful if the pilot not flying checked in on each new frequency above 10;000 FT MSL with the speed restriction just to serve as a reminder to the flight crew as well as ATC.
The wake turbulence incident switched our attention from airspeed control to position of the wake turbulence aircraft. We should have paid closer attention to airspeed and MCP selection during the evolution.
B737-700 flight crew departing MDW reported exceeding charted 250 KT restriction in part because of distraction from wake vortex encounter.