MLG FLC MISHEARS CLRNC. DSNDS; RECEIVES TCASII RA.

Narrative

WE WERE INBOUND TO ATL ON THE ROME ARR ABOUT 20 NM NW ON THE 313 DEG RADIAL AT 12000 FT AND 300 KIAS. THE CAPT WAS FLYING THE MLG AND I WAS THE PNF. I RECEIVED A RADIO CALL FROM ATL APCH CTL WHICH I COULD NOT UNDERSTAND. I THOUGHT IT WAS SOMETHING ABOUT SLOWING TO 210 KTS; SO I ASKED THE CAPT IF HE THOUGHT THAT'S WHAT APCH WANTED. HE SAID NO. I THEN ASKED APCH CTL TO REPEAT THEIR XMISSION. AT THIS TIME THE CAPT STARTED A DSCNT TO 10000 FT AS HE THOUGHT THAT WAS WHAT APCH CTL HAD SAID. ATL APCH CAME BACK AND SAID SLOW TO 210 KTS. I ROGERED THEIR XMISSION; THEN NOTICED THE CAPT WAS DSNDING. I ASKED HIM IF WE WERE SUPPOSED TO DSND TO 10000 FT AND HE REPLIED YES. I WAS UNSURE AND IMMEDIATELY ASKED ATL APCH WHAT ALT WE WERE SUPPOSED TO BE AT. APCH CTL SEEMED UNSURE AND FINALLY SAID 11000 FT. WE STARTED LEVELING AT 11000 FT AND WE RECEIVED A TA ON THE TCASII. THIS TA QUICKLY WENT TO AN RA WHICH SHOWED A 4000 FPM RATE OF CLB TO AVOID A COLLISION. AS THE CAPT STARTED THE CLB I RADIOED ATL APCH THAT WE WERE CLBING FOR A TCASII RA. I NOTICED AN MLG Y AT OUR 12 O'CLOCK WHO APPEARED TO BE CLBING OUT AFTER DEPARTING ATL. ATL APCH CTL QUICKLY CAME BACK AND TOLD US TO TURN TO 090 DEGS. WE STARTED THE TURN AND AT ABOUT 600 FT OF CLB TO 11600 FT THE RA DISAPPEARED COMPLETELY. BTWN OUR CLB AND TURN; AND THE MLG Y LEVEL OFF AT 10000 FT; WE NEVER GOT CLOSER THAN 1500 FT. ONE OF THE CONTRIBUTING FACTORS TO THIS INCIDENT WAS THE VERY BUSY RADIO XMISSIONS ON ATL APCH CTL'S FREQ. WHEN 1 CTLR IS FORCED TO WORK THAT MANY ACFT AT ONCE AND ANYTHING OUT OF THE ORDINARY HAPPENS; THEN PROBS SNOWBALL. PROBABLY THE MLG Y WOULD HAVE LEVELED OFF AT 10000 FT AND WE WOULD HAVE BEEN AT 11000 FT AND TCASII WOULD HAVE KEPT US APART. BUT AT ONE TIME AT LEAST ONE PLT IN OUR COCKPIT THOUGHT APCH CTL HAD CLRED US TO 10000 FT.