ARTCC RADAR CTLR HAVING BEEN GIVEN CTL OF AN FK10 F0R DSCNT IN ADJACENT SECTOR'S AIRSPACE STARTED THE ACFT DOWN THROUGH ANOTHER ACFT'S ALT; A DC9 AT FL290 AND OPPOSITE DIRECTION TFC. THE ADJACENT RADAR CTLR SAW THE POTENTIAL CONFLICT AND WARNED THE OTHER CTLR AND BOTH CTLRS TURNED THEIR TFC; BUT LTSS OCCURRED.

Narrative

RADAR AND RADAR ASSOCIATE STAFFED THE ZOB-DET SECTOR. WORKLOAD AND COMPLEXITY WERE AVERAGE FOR THE SECTOR. ACFT #1; ACR X WAS NWBOUND ON J-34 APPROX 20 MI SE OF CRL VORTAC; HANDED OFF TO DET SECTOR BUT STILL IN SKY SECTOR AIRSPACE. ACFT #2; ACR Y WAS SEBOUND ON J-34 APPROX 20 MI NW OF CRL; HANDED OFF AND SWITCHED TO SKY SECTOR BUT STILL IN DET SECTOR AIRSPACE. ACR X WAS INBOUND TO GRAND RAPIDS AND NEEDED TO START DOWN SOON DUE TO PROX OF THE FIELD AND OTHER TFC THAT WOULD OTHERWISE BECOME A FACTOR. SKY SECTOR GRANTED CTL FOR DSCNT OF ACR X TO THE DET SECTOR ASSOCIATE CTLR; WHO INFORMED THE DET RADAR CTLR. ACR X WAS ISSUED CLRNC TO FL240 AND ACR Y (OPPOSITE DIRECTION) WAS OVERLOOKED AS TFC. AFTER REALIZING THAT DET SECTOR WAS NOT PROVIDING ADEQUATE SEPARATION; THE SKY-R CTLR QUESTIONED DET-R. BOTH CTLRS TURNED THEIR RESPECTIVE ACFT L. ADDITIONALLY; ACR X WAS TOLD TO STOP DSCNT AT FL300. SEPARATION WAS LOST WITH 1000 FT VERT AND 2.4 MI LATERAL. THE DET RADAR CTLR MAY HAVE OVERLOOKED THE IMMEDIATE TFC IN AN EFFORT TO RESOLVE SECONDARY AND TERTIARY CONFLICTS.