Narrative:

I was administering on-the-job training at the carlton radar position. The traffic was very busy and complex. 2 successive inbounds to detroit metropolitan airport were involved (air carrier X and air carrier Y.) air carrier Y overtook air carrier X at the same altitude and loss of separation occurred. Air carrier Y was changed to my frequency at a later than usual time and this aircraft was faster than I realized. I allowed the trainee to work this traffic even though it was very busy. Nobody, including the associate controller and an observing supervisor noticed the overtake until it was too late. Corrective actions were taken but it did not stop the error. Supplemental information from acn 194197: air carrier X was being stepped down on top of other aircraft. Air carrier Y 15 mi never checked in, or never switched. Air carrier Y finally tracked down and called was descend to a clean altitude, air carrier X was being stepped down on top of and the overtake was overlooked. The traffic complexity was extreme. Air carrier Y was turned out to alleviate the overtake, but too late. Supplemental information from acn 194179: I was working radar associate position at the crl sector at ZOB at the time of occurrence. 2 passenger jets inbound to detroit metropolitan were descending to cross outer fix when the first one was given 120 with the back one at 160 and overtaking the first.

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Original NASA ASRS Text

Title: ACR Y DSCNT TO OCCUPIED ALT OVERTAKE HAD LTSS FROM ACR X. SYS ERROR.

Narrative: I WAS ADMINISTERING ON-THE-JOB TRAINING AT THE CARLTON RADAR POS. THE TFC WAS VERY BUSY AND COMPLEX. 2 SUCCESSIVE INBOUNDS TO DETROIT METRO ARPT WERE INVOLVED (ACR X AND ACR Y.) ACR Y OVERTOOK ACR X AT THE SAME ALT AND LOSS OF SEPARATION OCCURRED. ACR Y WAS CHANGED TO MY FREQ AT A LATER THAN USUAL TIME AND THIS ACFT WAS FASTER THAN I REALIZED. I ALLOWED THE TRAINEE TO WORK THIS TFC EVEN THOUGH IT WAS VERY BUSY. NOBODY, INCLUDING THE ASSOCIATE CTLR AND AN OBSERVING SUPVR NOTICED THE OVERTAKE UNTIL IT WAS TOO LATE. CORRECTIVE ACTIONS WERE TAKEN BUT IT DID NOT STOP THE ERROR. SUPPLEMENTAL INFO FROM ACN 194197: ACR X WAS BEING STEPPED DOWN ON TOP OF OTHER ACFT. ACR Y 15 MI NEVER CHKED IN, OR NEVER SWITCHED. ACR Y FINALLY TRACKED DOWN AND CALLED WAS DSND TO A CLEAN ALT, ACR X WAS BEING STEPPED DOWN ON TOP OF AND THE OVERTAKE WAS OVERLOOKED. THE TFC COMPLEXITY WAS EXTREME. ACR Y WAS TURNED OUT TO ALLEVIATE THE OVERTAKE, BUT TOO LATE. SUPPLEMENTAL INFO FROM ACN 194179: I WAS WORKING RADAR ASSOCIATE POS AT THE CRL SECTOR AT ZOB AT THE TIME OF OCCURRENCE. 2 PAX JETS INBOUND TO DETROIT METRO WERE DSNDING TO CROSS OUTER FIX WHEN THE FIRST ONE WAS GIVEN 120 WITH THE BACK ONE AT 160 AND OVERTAKING THE FIRST.

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.