Narrative:

Our flight was being vectored by ord approach control as we were being sequenced 5 mi behind a heavy B747 according to our TCASII display. We first encountered some of the B747's wash while on base with our assigned speed of 210 KTS. Just as we were going to contact our controller for a slower speed for spacing, he was already in the process of contacting us with the slower speed of 180 KTS. This helped to counter the wash. As we turned onto final and were cleared for the runway 9R approach, we were assigned a tower frequency, however, during this transmission, we encountered heavier wash that turned into moderate turbulence. For safety of flight, I had the first officer slow the aircraft down for spacing along with a power additive so as to help stabilize our situation as we kept the wings level. The wake turbulence lasted approximately 15 seconds and our approach controller was extremely busy on our frequency and we were not able to get in 3 different xmissions as he maintained a continuous 1-WAY communications stream without complete feedback. Since we were previously assigned the tower frequency, we went over to them only to be told that our approach controller needed us back on his frequency. We returned and were immediately chided by him with 'must be nice to do anything that you like.' as I discussed with the ord approach supervisor over the telephone after we had arrived at our gate, there were no complete xmissions to our controller nor to us as this situation later revealed because of their excessive communication demands. I was later told that the controller had wanted to take us out of the pattern and I then told the supervisor that this was not practical since it was necessary to keep our wings level until we had stabilized flight conditions.

Related reports:

Google
 

Original NASA ASRS Text

Title: LNDG MD90 AT ORD ENCOUNTERS WAKE TURB BEHIND B747.

Narrative: OUR FLT WAS BEING VECTORED BY ORD APCH CTL AS WE WERE BEING SEQUENCED 5 MI BEHIND A HVY B747 ACCORDING TO OUR TCASII DISPLAY. WE FIRST ENCOUNTERED SOME OF THE B747'S WASH WHILE ON BASE WITH OUR ASSIGNED SPD OF 210 KTS. JUST AS WE WERE GOING TO CONTACT OUR CTLR FOR A SLOWER SPD FOR SPACING, HE WAS ALREADY IN THE PROCESS OF CONTACTING US WITH THE SLOWER SPD OF 180 KTS. THIS HELPED TO COUNTER THE WASH. AS WE TURNED ONTO FINAL AND WERE CLRED FOR THE RWY 9R APCH, WE WERE ASSIGNED A TWR FREQ, HOWEVER, DURING THIS XMISSION, WE ENCOUNTERED HEAVIER WASH THAT TURNED INTO MODERATE TURB. FOR SAFETY OF FLT, I HAD THE FO SLOW THE ACFT DOWN FOR SPACING ALONG WITH A PWR ADDITIVE SO AS TO HELP STABILIZE OUR SIT AS WE KEPT THE WINGS LEVEL. THE WAKE TURB LASTED APPROX 15 SECONDS AND OUR APCH CTLR WAS EXTREMELY BUSY ON OUR FREQ AND WE WERE NOT ABLE TO GET IN 3 DIFFERENT XMISSIONS AS HE MAINTAINED A CONTINUOUS 1-WAY COMS STREAM WITHOUT COMPLETE FEEDBACK. SINCE WE WERE PREVIOUSLY ASSIGNED THE TWR FREQ, WE WENT OVER TO THEM ONLY TO BE TOLD THAT OUR APCH CTLR NEEDED US BACK ON HIS FREQ. WE RETURNED AND WERE IMMEDIATELY CHIDED BY HIM WITH 'MUST BE NICE TO DO ANYTHING THAT YOU LIKE.' AS I DISCUSSED WITH THE ORD APCH SUPVR OVER THE TELEPHONE AFTER WE HAD ARRIVED AT OUR GATE, THERE WERE NO COMPLETE XMISSIONS TO OUR CTLR NOR TO US AS THIS SIT LATER REVEALED BECAUSE OF THEIR EXCESSIVE COM DEMANDS. I WAS LATER TOLD THAT THE CTLR HAD WANTED TO TAKE US OUT OF THE PATTERN AND I THEN TOLD THE SUPVR THAT THIS WAS NOT PRACTICAL SINCE IT WAS NECESSARY TO KEEP OUR WINGS LEVEL UNTIL WE HAD STABILIZED FLT CONDITIONS.

Data retrieved from NASA's ASRS site as of July 2007 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.