Narrative:

Air carrier in cruise at FL280 deviating for thunderstorms was told by ATC (atl communication frequency) to descend to FL270, 'traffic 12 O'clock at 280, no one is talking to him.' began descent immediately and was given turn to left heading 270 degrees, then in a concerned voice, 'turn to 240 and expedite to 270.' traffic righted visually and appeared to be at our altitude (FL270). First officer questioned altitude of traffic and controller responded for us to climb to FL280. I determined descent was best escape from midair situation and evaded with descent and 30-45 degree bank turn to left. Descent stopped at 25700'. Returned to FL260 and questioned ATC about desired altitude. ATC responded '260 is fine; thanks for the help.' other traffic was air carrier Y. Supplemental information from acn 156315: while deviating around WX to the psk VOR on a heading of approximately 190 degrees at FL280 we received a clearance from ATC to another clearance to descend immediately to FL270 and to turn to a heading of 330 degrees. Prior to reaching FL280 and a heading of 330 degrees we were instructed to maintain our current heading of 270 degrees and to climb back to FL280 and stand by. The controller was very busy and I think we were given a clearance beginning. However, due to immediate nature of the clearance and frequency congestion I was unable to question the controller. After the incident another controller came on the frequency and issued us another clearance on course and told us there had been an ATC error.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: ACR IN CRUISE AT FL280 DEVIATING FOR TSTMS WAS TOLD BY ATC (ATL COM FREQ) TO DSND TO FL270, 'TFC 12 O'CLOCK AT 280, NO ONE IS TALKING TO HIM.' BEGAN DSNT IMMEDIATELY AND WAS GIVEN TURN TO LEFT HDG 270 DEGS, THEN IN A CONCERNED VOICE, 'TURN TO 240 AND EXPEDITE TO 270.' TFC RIGHTED VISUALLY AND APPEARED TO BE AT OUR ALT (FL270). F/O QUESTIONED ALT OF TFC AND CTLR RESPONDED FOR US TO CLB TO FL280. I DETERMINED DSNT WAS BEST ESCAPE FROM MIDAIR SITUATION AND EVADED WITH DSNT AND 30-45 DEG BANK TURN TO LEFT. DSNT STOPPED AT 25700'. RETURNED TO FL260 AND QUESTIONED ATC ABOUT DESIRED ALT. ATC RESPONDED '260 IS FINE; THANKS FOR THE HELP.' OTHER TFC WAS ACR Y. SUPPLEMENTAL INFO FROM ACN 156315: WHILE DEVIATING AROUND WX TO THE PSK VOR ON A HDG OF APPROX 190 DEGS AT FL280 WE RECEIVED A CLRNC FROM ATC TO ANOTHER CLRNC TO DSND IMMEDIATELY TO FL270 AND TO TURN TO A HDG OF 330 DEGS. PRIOR TO REACHING FL280 AND A HDG OF 330 DEGS WE WERE INSTRUCTED TO MAINTAIN OUR CURRENT HDG OF 270 DEGS AND TO CLB BACK TO FL280 AND STAND BY. THE CTLR WAS VERY BUSY AND I THINK WE WERE GIVEN A CLRNC BEGINNING. HOWEVER, DUE TO IMMEDIATE NATURE OF THE CLRNC AND FREQ CONGESTION I WAS UNABLE TO QUESTION THE CTLR. AFTER THE INCIDENT ANOTHER CTLR CAME ON THE FREQ AND ISSUED US ANOTHER CLRNC ON COURSE AND TOLD US THERE HAD BEEN AN ATC ERROR.

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.