APCH CTLR CALLED TFC TO 757 ON VECTOR AT 11000 FT. 757 GOT TCASII RA ON FK28 CLBING TO 10000 FT AND FOLLOWED RA TO DSND. RESULT WAS LTSS WHICH WAS ALMOST AN NMAC.

Narrative

ACR X (B757) WAS AT 11000 FT. TFC WAS ISSUED TO ACR X. TFC WAS AN ACR Y FK28 DEP. TFC WAS ISSUED AT 11 O'CLOCK AND 5 MI SEBOUND OUT OF 8200 FT FOR 10000 FT. ACR X SAID HE FINALLY GOT THE TFC IN SIGHT; BUT ALSO STATED THAT HE HAD A TCASII RESOLUTION. ACR X DSNDED TO 10600 FT. AT THE TIME HE STATED THIS; TARGETS MERGED AND 600 FT VERT SEPARATION EXISTED. IF THE PLT OF ACR X DID NOT GET VISUAL ON HIS TFC; THERE MOST LIKELY COULD HAVE BEEN A MIDAIR COLLISION. ALSO WHAT SAVED THIS SIT WAS; AT THE TIME OF THIS INCIDENT; THE ACFT WERE IN VMC CONDITIONS. SUPPLEMENTAL INFO FROM ACN 262998: MY ACFT WAS LEVEL AT 11000 FT BEING VECTORED FOR APCH. ATC ADVISED CLBING TFC AT 12 O'CLOCK. THE ONLY ACFT I SAW AT THE TIME APPEARED TO BE ABOVE US. THE TCASII THEN COMMANDED A DSCNT NOW. NOT SEEING ANY ACFT IN CONFLICT; I TOLD THE FO TO DSND NOW. AT 10600 FT; I SAW AN ACR DC9 OR FOKKER AT 12:30 POS AND APPROX 500-600 FT BELOW ME. I TOLD THE FO TO LEVEL OFF AND I TOLD ATC I HAD A TCASII RA TO DSND. I WAS AT 10600 FT AND RETURNING TO 11000 FT. ATC QUESTIONED THAT TCASII CALLED FOR DSCNT AND I CONFIRMED IT HAD. MY GUESS IS THAT MY TCASII JUDGED HIS RAPID CLB TO 10000 FT AND COMMANDED MY DSCNT NOT KNOWING THE OTHER ACFT WAS GOING TO LEVEL AT 10000 FT.