McDonnell Douglas Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 120; Flight Crew Total 8000; Flight Crew Type 1200
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Wake Vortex Encounter
General None Reported / Taken
Procedure; Environment - Non Weather Related
Chicago Center was extremely busy with arrivals. I was assigned 300 knots on the WATSN 2 arrival and told to switch to 133.625. I checked in with him and did not mention the 300 knots speed assignment on check in nor did he ask. I was watching the aircraft ahead of me on TCAS get closer and closer. I called three times to confirm they still wanted 300 knots with no reply; maybe I stepped on someone and blocked the question. As our range continued to dwindle I slowed to 250. Just as we had slowed down two controllers started to harangue me about why I slowed down we were assigned 300. One of the exasperated controllers assigned me 300 knots and 7000 FT. Moments later I asked them to confirm 300 below 10000 FT and another voice on the frequency said 'no 250 thanks for asking'. We ended up landing less than 5 miles behind a 747 where we encountered wake turbulence on short final. If we hadn't slowed down when we did I think we might have been too close to the preceding aircraft and gone around.Clearly this was a stressful environment but without good two way communication. I am obliged to operate my airplane as safely as I could.
Mcdonnell Douglas Widebody Captain reported encountering wake vortex in trail of a B747 on approach to ORD. Speed assignment from ATC was cited as a factor.