ATX-SMT OVERTAKEN BY MLT WHILE BOTH WERE ON DEP VECTORS CLIMBING RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative

AMONG THE NUMEROUS DEPS; SMT X DEPARTED ON A TWR ASSIGNED HDG OF 090 DEGS CLBING TO 3000'. I RADAR IDENTED SMT X AND CLBED SMT X TO 5000'; HDG 090 DEGS. APPROX 2 MINS LATER MLT Y DEPARTED ON TWR ASSIGNED HDG OF 090 DEGS; CLBING TO 3000'. MLT Y HAD AN OVERTAKE SPD OF 70-80 KTS ON SMT X; CLOSING RAPIDLY. SMT X WAS OUT OF 3100' CLBING. MLT Y WAS OUT OF AT LEAST 2000' AND APPROX 2.5 NM BEHIND SMT X. I ASSUMED TWR HAD SEP VIA VISUAL SEP RULES; BUT AS I QUERIED MLT Y TO VERIFY HE HAD SMT X IN SIGHT; MLT Y RESPONDED TO MY TFC ADVISORY BY STATING; 'WE'RE LOOKING.' REALIZING HE DID NOT HAVE SMT X IN SIGHT; MY RADAR ASSISTANT COORDINATED WITH FINAL TO TURN SMT X INTO THEIR AIRSPACE. I TURNED SMT X TO 130 DEGS TO ESTABLISH COURSE DIVERGENCE SEP. THIS INCIDENT WAS RPTED TO SUPVR PERSONNEL AS I WANTED AN EXPLANATION FROM THE TWR. THE TWR CTLRS ADMITTED FAULT; STATING TRNING AS A FACTOR. A TRNEE AND INSTR WERE WORKING THE LCL CTLR POS. THE ARTS PLAYBACK TAPE SHOWED LESS THAN 3 MI SEP; BUT DUE TO MAINT WORK BEING DONE ON THE ARTS EQUIP; NO READOUT OF MLT Y'S ALT READOUT WAS AVAILABLE. I DROPPED THE CHARGES AGAINST THE 2 LCL CTLRS AS I COULD NOT RECALL THE SPECIFIC ALT OF MLT Y. THE 2 CTLRS HAVE BEEN COUNSELED. TO AVOID THIS INCIDENT RECURRING; CTLRS HAVE TO BE VERY AWARE OF ACFT SPDS AND OVERTAKE CAPABILITIES.