Narrative:

We were flying the rome arrival into atl. Our clearance was to cross the dalas fix at 14000 MSL and 250 KIAS. As we were descending through 15800 our TCASII gave us a traffic warning. The TCASII changed immediately to a 'climb!' RA. I aggressively added power and changed from a descent to a climb. We bottomed out at 15600 and then climbed rapidly to about 17000-18000 MSL. Due to a stuck microphone, ZTL's attempt to give us a traffic warning was blocked. Both our TCASII and ZTL showed the targets merged with only 100 ft altitude difference. The traffic at 15500 was VFR and no contact was made by radio and it appeared to make avoidance maneuvers. We never saw the other aircraft. Score a save for TCASII! The problem here is that ZTL knew about the VFR traffic before the conflict and still cleared us to descend through its altitude! Their only attempt at warning us came too late. We will never know how close we came or if we would have hit the other aircraft but we should never have been cleared below 16000.

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Original NASA ASRS Text

Title: FLC OF AN MLG ACR ACFT TOOK EVASIVE ACTION DURING AN ARR DSCNT IN RESPONSE TO A TCASII RA.

Narrative: WE WERE FLYING THE ROME ARR INTO ATL. OUR CLRNC WAS TO CROSS THE DALAS FIX AT 14000 MSL AND 250 KIAS. AS WE WERE DSNDING THROUGH 15800 OUR TCASII GAVE US A TFC WARNING. THE TCASII CHANGED IMMEDIATELY TO A 'CLB!' RA. I AGGRESSIVELY ADDED PWR AND CHANGED FROM A DSCNT TO A CLB. WE BOTTOMED OUT AT 15600 AND THEN CLBED RAPIDLY TO ABOUT 17000-18000 MSL. DUE TO A STUCK MIKE, ZTL'S ATTEMPT TO GIVE US A TFC WARNING WAS BLOCKED. BOTH OUR TCASII AND ZTL SHOWED THE TARGETS MERGED WITH ONLY 100 FT ALT DIFFERENCE. THE TFC AT 15500 WAS VFR AND NO CONTACT WAS MADE BY RADIO AND IT APPEARED TO MAKE AVOIDANCE MANEUVERS. WE NEVER SAW THE OTHER ACFT. SCORE A SAVE FOR TCASII! THE PROB HERE IS THAT ZTL KNEW ABOUT THE VFR TFC BEFORE THE CONFLICT AND STILL CLRED US TO DSND THROUGH ITS ALT! THEIR ONLY ATTEMPT AT WARNING US CAME TOO LATE. WE WILL NEVER KNOW HOW CLOSE WE CAME OR IF WE WOULD HAVE HIT THE OTHER ACFT BUT WE SHOULD NEVER HAVE BEEN CLRED BELOW 16000.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.