Narrative:

Air carrier X was descending into ord via the pmm 4 arrival. Air carrier Y was nwbound level at 16000 ft direct osh..atw. Air carrier Y was given a 360 degree heading so that another ord inbound could be descending on time. I was unaware that there were 100 KT winds out of the wnw, and the 360 degrees ended up being more like a 20 degree or 30 degree heading. When I saw the first radar hit after issuing the heading, I could hardly believe it because 4 and 5 mi target jumps are common on this area. Nevertheless, I instructed air carrier X to turn 10 degrees left and expedite through 15000 ft. Obviously this action was not quite enough, compounded by the fact that pilot only gave me 2000 FPM. I should have told the pilot the rate I needed and issued more of a turn, so I accept full responsibility. But it should be noted that although the pmm 4 arrival is one of the busiest inbound corridors in the world, the radar coverage between the kubbs intersection and the tadds intersection is simply not very good. 'Target jumps' are common, sometimes even one 'airplane' jumping behind another because of erroneous radar information. This can be unsettling and downright scary. After a while, a controller will learn to rely more on the 'history' of where the aircraft has been, rather than the new situation 'hit' for speed control and separation. Controllers have been complaining about this for yrs, but nothing is ever done.

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Original NASA ASRS Text

Title: NOT CONSIDERING HIGH WING CONDITION, ZAU CTLR MISJUDGES SPACING REQUIRED BTWN AN INBOUND B733 AND AN OUTBOUND E129, RESULTING IN AN OPERROR.

Narrative: ACR X WAS DSNDING INTO ORD VIA THE PMM 4 ARR. ACR Y WAS NWBOUND LEVEL AT 16000 FT DIRECT OSH..ATW. ACR Y WAS GIVEN A 360 DEG HDG SO THAT ANOTHER ORD INBOUND COULD BE DSNDING ON TIME. I WAS UNAWARE THAT THERE WERE 100 KT WINDS OUT OF THE WNW, AND THE 360 DEGS ENDED UP BEING MORE LIKE A 20 DEG OR 30 DEG HDG. WHEN I SAW THE FIRST RADAR HIT AFTER ISSUING THE HDG, I COULD HARDLY BELIEVE IT BECAUSE 4 AND 5 MI TARGET JUMPS ARE COMMON ON THIS AREA. NEVERTHELESS, I INSTRUCTED ACR X TO TURN 10 DEGS L AND EXPEDITE THROUGH 15000 FT. OBVIOUSLY THIS ACTION WAS NOT QUITE ENOUGH, COMPOUNDED BY THE FACT THAT PLT ONLY GAVE ME 2000 FPM. I SHOULD HAVE TOLD THE PLT THE RATE I NEEDED AND ISSUED MORE OF A TURN, SO I ACCEPT FULL RESPONSIBILITY. BUT IT SHOULD BE NOTED THAT ALTHOUGH THE PMM 4 ARR IS ONE OF THE BUSIEST INBOUND CORRIDORS IN THE WORLD, THE RADAR COVERAGE BTWN THE KUBBS INTXN AND THE TADDS INTXN IS SIMPLY NOT VERY GOOD. 'TARGET JUMPS' ARE COMMON, SOMETIMES EVEN ONE 'AIRPLANE' JUMPING BEHIND ANOTHER BECAUSE OF ERRONEOUS RADAR INFO. THIS CAN BE UNSETTLING AND DOWNRIGHT SCARY. AFTER A WHILE, A CTLR WILL LEARN TO RELY MORE ON THE 'HISTORY' OF WHERE THE ACFT HAS BEEN, RATHER THAN THE NEW SIT 'HIT' FOR SPD CTL AND SEPARATION. CTLRS HAVE BEEN COMPLAINING ABOUT THIS FOR YRS, BUT NOTHING IS EVER DONE.

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.