Operational error occurred when a ZAU ARTCC radar controller attempted to descend an LR35 through the altitude of a citation jet level at FL310.

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Attributes
ACN	535925
Time
Date	200201
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : jvl.vortac
State Reference	IL
Altitude	msl bound lower : 24000 msl bound upper : 33000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	general aviation : personal
Make Model Name	Learjet 35
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zau.artcc
Operator	general aviation : corporate
Make Model Name	Cessna Citation Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Experience	controller military : 4 controller radar : 14 controller time certified in position1 : 9
ASRS Report	535935
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance
Consequence	faa : investigated
Miss Distance	horizontal : 28500 vertical : 100
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I received aircraft #1 from the sector above my sector descending to FL330. I had aircraft #2 (an overflt) wbound at FL310. Now I needed to get aircraft #1 down because he was landing at ugn. So, considering aircraft type (an LR35) and I ran out the vector lines and knew it would be tight, I told aircraft #1 to descend to FL240 and to expedite through FL290 and that I needed him out of FL290 in 1 min. His response was, 'center, that might be a little tight, but we'll give you our best try.' as the aircraft were closing (they were not nose-to-nose) I saw that it probably wasn't going to work. So I popped up a j-ball and turned both aircraft 20 degrees left when the overflt aircraft #2 was just about to bust the bottom edge of the j-ball. I asked the lear 35 to verify he was out of FL290. His response was, 'center, we're leaving FL300,' then unkeyed, then he rekeyed and said that in fact he was out of FL290. So, that was 7 seconds late/4.75 mi.

Original NASA ASRS Text

Title: OPERROR OCCURRED WHEN A ZAU ARTCC RADAR CTLR ATTEMPTED TO DSND AN LR35 THROUGH THE ALT OF A CITATION JET LEVEL AT FL310.

Narrative: I RECEIVED ACFT #1 FROM THE SECTOR ABOVE MY SECTOR DSNDING TO FL330. I HAD ACFT #2 (AN OVERFLT) WBOUND AT FL310. NOW I NEEDED TO GET ACFT #1 DOWN BECAUSE HE WAS LNDG AT UGN. SO, CONSIDERING ACFT TYPE (AN LR35) AND I RAN OUT THE VECTOR LINES AND KNEW IT WOULD BE TIGHT, I TOLD ACFT #1 TO DSND TO FL240 AND TO EXPEDITE THROUGH FL290 AND THAT I NEEDED HIM OUT OF FL290 IN 1 MIN. HIS RESPONSE WAS, 'CTR, THAT MIGHT BE A LITTLE TIGHT, BUT WE'LL GIVE YOU OUR BEST TRY.' AS THE ACFT WERE CLOSING (THEY WERE NOT NOSE-TO-NOSE) I SAW THAT IT PROBABLY WASN'T GOING TO WORK. SO I POPPED UP A J-BALL AND TURNED BOTH ACFT 20 DEGS L WHEN THE OVERFLT ACFT #2 WAS JUST ABOUT TO BUST THE BOTTOM EDGE OF THE J-BALL. I ASKED THE LEAR 35 TO VERIFY HE WAS OUT OF FL290. HIS RESPONSE WAS, 'CTR, WE'RE LEAVING FL300,' THEN UNKEYED, THEN HE REKEYED AND SAID THAT IN FACT HE WAS OUT OF FL290. SO, THAT WAS 7 SECONDS LATE/4.75 MI.

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.