Narrative:

Aircraft #1 and aircraft #2 both were landing cvg. Aircraft #1 was on STAR, cince arrival to cvg and slowed to 250 KTS. Aircraft #2 was coordinated, slowed to 250 KTS by previous center. Aircraft #2 was vectored to go beyond aircraft #1 and then cleared direct to bowrr to join the cince arrival. When aircraft #2 joined the cince arrival, he was 7 mi behind aircraft #1 and over 100 KTS faster! It was never noticed by radar controller and radar associate that aircraft #2's airspeed was faster than the 250 KT assignment until it was too late. Conflict alert activated that showed loss of separation impending. Aircraft #1 was on low altitude sector frequency and radar controller asked low altitude controller to descend aircraft #1. Radar controller vectored aircraft #2 3 times to the right to maintain separation, however, separation was lost. Why did this happen? The data blocks have the ability to display '4TH line information.' I entered the 250 KT speed restr on the data block of aircraft #2 due to previous center coordination. My scan did not include scrutiny of aircraft #2's actual ground speed. It was assumed that he was always at 250 KTS. After separation was lost, the radar controller issued 250 KTS to aircraft #2 and aircraft #2 responded that he would slow to 250 KTS. So, he was never at 250 KTS as coordination by the previous center controller. Also, if the radar controller had only descended aircraft #2 to FL250 and cleared him to bowrr, vertical separation would have been maintained with the 100+ KT overtake from behind. How to prevent: accurately scan what aircraft is really doing. Look at ground speed! Also, always have a form of separation applied at all times. With only 5 mi separation allowed, vectoring for 7 mi was pretty tight. Vertical separation would have saved this error from occurring. Supplemental information from acn 616122: air carrier Y was issued 250 KTS from a previous sector, so 250 KTS was indicated in 4TH line of data block. I failed to observe the ground speed that didn't coincide with what he was assigned. I requested the low altitude sector descent to help me out. That controller happened to be a flow controller getting his proficiency for the month. I didn't get much help with a standard descent. Possibly a full time controller working the other aircraft could have helped me out.

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Original NASA ASRS Text

Title: ZID RADAR ASSOCIATE AND RADAR CTLR FAIL TO RECOGNIZE A B757 OVERTAKE AN MD80 ON APCH TO CVG EXPECTING THE B757 TO HAVE BEEN REDUCED TO THE SPD OF THE PRECEDING MD80.

Narrative: ACFT #1 AND ACFT #2 BOTH WERE LNDG CVG. ACFT #1 WAS ON STAR, CINCE ARR TO CVG AND SLOWED TO 250 KTS. ACFT #2 WAS COORDINATED, SLOWED TO 250 KTS BY PREVIOUS CTR. ACFT #2 WAS VECTORED TO GO BEYOND ACFT #1 AND THEN CLRED DIRECT TO BOWRR TO JOIN THE CINCE ARR. WHEN ACFT #2 JOINED THE CINCE ARR, HE WAS 7 MI BEHIND ACFT #1 AND OVER 100 KTS FASTER! IT WAS NEVER NOTICED BY RADAR CTLR AND RADAR ASSOCIATE THAT ACFT #2'S AIRSPD WAS FASTER THAN THE 250 KT ASSIGNMENT UNTIL IT WAS TOO LATE. CONFLICT ALERT ACTIVATED THAT SHOWED LOSS OF SEPARATION IMPENDING. ACFT #1 WAS ON LOW ALT SECTOR FREQ AND RADAR CTLR ASKED LOW ALT CTLR TO DSND ACFT #1. RADAR CTLR VECTORED ACFT #2 3 TIMES TO THE R TO MAINTAIN SEPARATION, HOWEVER, SEPARATION WAS LOST. WHY DID THIS HAPPEN? THE DATA BLOCKS HAVE THE ABILITY TO DISPLAY '4TH LINE INFO.' I ENTERED THE 250 KT SPD RESTR ON THE DATA BLOCK OF ACFT #2 DUE TO PREVIOUS CTR COORD. MY SCAN DID NOT INCLUDE SCRUTINY OF ACFT #2'S ACTUAL GND SPD. IT WAS ASSUMED THAT HE WAS ALWAYS AT 250 KTS. AFTER SEPARATION WAS LOST, THE RADAR CTLR ISSUED 250 KTS TO ACFT #2 AND ACFT #2 RESPONDED THAT HE WOULD SLOW TO 250 KTS. SO, HE WAS NEVER AT 250 KTS AS COORD BY THE PREVIOUS CTR CTLR. ALSO, IF THE RADAR CTLR HAD ONLY DSNDED ACFT #2 TO FL250 AND CLRED HIM TO BOWRR, VERT SEPARATION WOULD HAVE BEEN MAINTAINED WITH THE 100+ KT OVERTAKE FROM BEHIND. HOW TO PREVENT: ACCURATELY SCAN WHAT ACFT IS REALLY DOING. LOOK AT GND SPD! ALSO, ALWAYS HAVE A FORM OF SEPARATION APPLIED AT ALL TIMES. WITH ONLY 5 MI SEPARATION ALLOWED, VECTORING FOR 7 MI WAS PRETTY TIGHT. VERT SEPARATION WOULD HAVE SAVED THIS ERROR FROM OCCURRING. SUPPLEMENTAL INFO FROM ACN 616122: ACR Y WAS ISSUED 250 KTS FROM A PREVIOUS SECTOR, SO 250 KTS WAS INDICATED IN 4TH LINE OF DATA BLOCK. I FAILED TO OBSERVE THE GND SPD THAT DIDN'T COINCIDE WITH WHAT HE WAS ASSIGNED. I REQUESTED THE LOW ALT SECTOR DSCNT TO HELP ME OUT. THAT CTLR HAPPENED TO BE A FLOW CTLR GETTING HIS PROFICIENCY FOR THE MONTH. I DIDN'T GET MUCH HELP WITH A STANDARD DSCNT. POSSIBLY A FULL TIME CTLR WORKING THE OTHER ACFT COULD HAVE HELPED ME OUT.

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.