ACR X HAD TCASII RA WITH INTRAIL CPR Y.

Narrative

WHILE WORKING W DEP AT O'HARE; I WAS VECTORING SEVERAL ACFT IN TRAIL TO PROVIDE THE 7 MI REQUIRED SPACING OVER IOW FIX. I ASSIGNED ACR X 13000 AND INSTRUCTED HIM TO INCREASE SPD TO 300 KTS OR GREATER OUT 10000. I HAD CPR Y AT 9000 APPROX 3-4 MI BEHIND ACR X. I CLBED CPR Y TO 13000 AND ASSIGNED 250 KTS. I WAITED FOR THE SPACING BTWN THE TWO ACFT TO INCREASE TO 7 MI; AND THEN TOLD CPR Y TO RESUME NORMAL SPD. I SWITCHED ACR X TO THE CTR. APPROX 2 MIN LATER; ACR X CAME BACK TO ME; AND ASKED IF I HAD HAD TFC BEHIND HIM ON CLBOUT. I STATED YES; AND DESCRIBED THE SCENARIO. THE PLT INFORMED ME THAT HE HAD A TCASII RA INSTRUCTING HIM TO DSND. ALTHOUGH TCASII IS A NEEDED ADDITION TO THE AIR TFC SYS; HAD THE PLT FOLLOWED THE RA; HE WOULD HAVE DSNDED BELOW 10000; REDUCED HIS SPD; AND BEEN PREOCCUPIED WITH POSSIBLE TFC. THIS WOULD HAVE HAD A 'RIPPLE' EFFECT ON AT LEAST 7 OTHER ACFT ROUTED OVER IOW. AT THE PRESENT RATE OF INSTALLATION; MOST AIR CARRIERS WILL HAVE TCASII BY 1993. THE INCREASE IN TCASII INCIDENT WILL HAVE AN EFFECT ON THE SAFETY AND EFFICIENCY OF THE ATC SYS; UNLESS WE ARE ABLE TO REFINE HOW THE EQUIP IS INTEGRATED WITHIN THE SYS.