Mcdonnell douglas widebody captain reported encountering wake vortex in trail of a B747 on approach ...

Attributes
ACN	1221208
Time
Date	201411
Local Time Of Day	0601-1200
Place
Locale Reference	ORD.Airport
State Reference	IL
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Make Model Name	McDonnell Douglas Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR WATSN2
Flight Plan	IFR
Aircraft 2
Make Model Name	B747 Undifferentiated or Other Model
Flight Phase	Final Approach
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 8000 Flight Crew Type 1200
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Deviation - Speed All Types Inflight Event / Encounter Wake Vortex Encounter

Narrative:

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.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

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.