DEV CTLR GAVE PREMATURE DESCENT CLRNC TO SMT RESULTING IN LESS THAN STANDARD SEPARATION WITH SLOWER SMA.

Narrative

WBOUND GENERAL AVIATION ACFT AT 10000'. SOUTHWBOUND COMMUTER ACFT AT 11000'; NE OF; AND FASTER THAN; GA ACFT. COMMUTER ACFT WAS DESCENDED TO 9000' WITH LESS THAN REQUIRED SEPARATION. ERROR WAS NOTED WITHIN SECONDS BUT ACFT ALREADY BEGUN DESCENT. ACFT WAS CLIMBED BACK TO 11000' BUT HAD DESCENDED TO 10600'. ERROR WAS NOTICED BY ME AND BY 'CONFLICT ALERT' FEATURE. A TRAINEE WAS WORKING THE FREQ. I WAS MONITORING HIM; WORKING THE ASSOCIATE CTLR POSITION; AND WORKING THE ASSISTANT CTLR POSITION (FLT STRIP PRINTER). TRAINEE SAID HE THOUGHT HE HAD 5 MILES SEPARATION. HE SHOULD HAVE USED '5-MILE' CIRCLE TO ASSURE IT. I WAS TEARING A STRIP OFF THE PRINTER WHEN IT OCCURRED. WHEN I LOOKED BACK AT THE RADAR; IT WAS TOO LATE; EVEN THOUGH IT WAS ONLY A FEW SECONDS. HAD THE SECTOR BEEN PROPERLY STAFFED; THE INCIDENT WOULD NOT HAVE OCCURRED. I WOULD HAVE BEEN ABLE TO WATCH THE RADAR AND TRAINEE 100% OF THE TIME. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING INFORMATION: TFC VOLUME WAS LIGHT AND DID NOT WARRANT STAFFING OF THE ASSISTANT OR ASSOCIATE CTLR POS. RPTR WAS WATCHING A DEV THAT WAS VERY NEAR BECOMING POS QUALIFIED. HE DIVERTED HIS ATTN FROM HIS STUDENT TO THE FLT STRIP PRINTER AND IN A VERY SHORT PERIOD OF TIME THE DEV GAVE THE CLRNC TO DESCEND TO THE CTLR SMT THAT CAUSED THE LOSS OF SEP. NEITHER THE INSTR OR DEV KNEW WHY THE CLRNC WAS GIVEN FOR DSCNT WHEN LATERAL SEP DID NOT EXIST. (TYPE ACFT AND FURTHER INFO ON CTLR EXP LEVEL WAS ASCERTAINED.)