Narrative:

Air carrier X was wbound just south of J-64 and west of lmn. Air carrier Y was 8 mi behind and slightly south of X. X was cleared to deviation south. All previous aircraft had picked up about a 240-230 degree heading to skirt the thunderstorms. Most aircraft had gone towards sln, however, a few had gone north of lnk J-60/ X and Y were on approximately parallel headings about 240 degrees. Suddenly X began a left turn to 135 degrees. The controller working the radio tried to turn and descend the Y flight. Standard separation was lost, and at least one of the aircraft responded to a TCASII alert. I was the manual controller on this incident and I think that it would have been a good idea for the pilot to say something before he made such a drastic turn, even though he had been cleared to deviation. Thunderstorms and bad frequencys also contributed to the problem. Supplemental information from acn 273858: by the time air carrier X re-established communication and received clearance to deviation south of course we were getting quite close to the storm. To remain clear of the storm we turned close to 90 degrees to our route of flight. When we received the climb RA, we initiated a climb, notified ATC, who instructed us to level at FL330. The other aircraft passed below and to the left as we followed the climb RA. The controller was trying to resolve the developing conflict when we received the RA. The controller probably did not expect us to turn as far south as we did.

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Original NASA ASRS Text

Title: ACR X WX DEV HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR X WAS WBOUND JUST S OF J-64 AND W OF LMN. ACR Y WAS 8 MI BEHIND AND SLIGHTLY S OF X. X WAS CLRED TO DEV S. ALL PREVIOUS ACFT HAD PICKED UP ABOUT A 240-230 DEG HDG TO SKIRT THE TSTMS. MOST ACFT HAD GONE TOWARDS SLN, HOWEVER, A FEW HAD GONE N OF LNK J-60/ X AND Y WERE ON APPROX PARALLEL HDGS ABOUT 240 DEGS. SUDDENLY X BEGAN A L TURN TO 135 DEGS. THE CTLR WORKING THE RADIO TRIED TO TURN AND DSND THE Y FLT. STANDARD SEPARATION WAS LOST, AND AT LEAST ONE OF THE ACFT RESPONDED TO A TCASII ALERT. I WAS THE MANUAL CTLR ON THIS INCIDENT AND I THINK THAT IT WOULD HAVE BEEN A GOOD IDEA FOR THE PLT TO SAY SOMETHING BEFORE HE MADE SUCH A DRASTIC TURN, EVEN THOUGH HE HAD BEEN CLRED TO DEV. TSTMS AND BAD FREQS ALSO CONTRIBUTED TO THE PROB. SUPPLEMENTAL INFO FROM ACN 273858: BY THE TIME ACR X RE-ESTABLISHED COM AND RECEIVED CLRNC TO DEV S OF COURSE WE WERE GETTING QUITE CLOSE TO THE STORM. TO REMAIN CLR OF THE STORM WE TURNED CLOSE TO 90 DEGS TO OUR RTE OF FLT. WHEN WE RECEIVED THE CLB RA, WE INITIATED A CLB, NOTIFIED ATC, WHO INSTRUCTED US TO LEVEL AT FL330. THE OTHER ACFT PASSED BELOW AND TO THE L AS WE FOLLOWED THE CLB RA. THE CTLR WAS TRYING TO RESOLVE THE DEVELOPING CONFLICT WHEN WE RECEIVED THE RA. THE CTLR PROBABLY DID NOT EXPECT US TO TURN AS FAR S AS WE DID.

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.