B737-700
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 67; Flight Crew Type 3441
Situational Awareness
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Environment - Non Weather Related; Human Factors; Procedure
We were flying the ILS 27R to ORD. When cleared for the approach level at 4;000 ft; we twice had to disconnect the autopilot from the aircraft wake ahead of us. Spacing was the usual 3 miles and winds were straight down the path at 40 kts. Other aircraft were radioing similar issues with wake.  I decided to hand fly the approach the rest of the way to better control the speed and avoid the wake. The Final Controller told us to slow to 170 kts and contact Tower. We were cleared to land by Tower and continued the approach at 170 kts. Spacing was holding at 3 miles; but as we approached the marker I noticed our spacing was closing faster than normal. At about 2.5 outside the marker I made the decision to start slowing to avoid going around. (Full disclosure; I have been in the exact situation before and had to go around twice on this approach.) What I misjudged was how fast the 737-700 slows down. We were at approach speed too early and the Tower asked our speed and instructions. We made the aircraft behind us go around from my error in speed control.
While on ILS 27R into ORD; we were experiencing wake turbulence from the aircraft ahead of us and appeared to be quickly closing the distance between us. We had been assigned 170 kts until the final approach fix 'SIBLY' and began slowing 2 miles prior to the fix to stop the closure. The Tower Controller queried our speed; and emphasized we were to hold 170 until the fix.
B737 flight crew reported slowing below assigned airspeed to avoid wake turbulence from aircraft ahead on approach to ORD; forcing traffic in trail of them to go around.