Narrative:

I was the radar controller at the houston ARTCC, lufkin specialty, alexandria high altitude sector. The manual position was combined. Approximately 9 aircraft were on frequency. Numerous turbulence reports (light to mod chop) were being made by aircraft at altitudes from FL250-FL350. No WX was depicted in the sector except for a southwest-northeast line of heavy thunderstorms from approximately lch..btr..40 mi south of mcb. This line was 80-100 mi south of all aircraft in the sector. At this point I noticed from the histories of air carrier X track that the aircraft had turned from an approximately 060 heading to northbound. I realized that on that heading there was a potential confliction with air carrier Y, but that the aircraft should pass 10-15 mi laterally. I put up a 'J-ring' on air carrier X just to be sure. After talking to another aircraft I noted that the histories of air carrier X track now showed him on an approximately 330 heading, putting him head on with air carrier Y (note: the computer generated vector length still showed the aircraft on an approximately 020 heading). Air carrier X was issued a descent to FL310 and told to expedite. The aircraft stated that would 'put us right back into this stuff'. Air carrier Y was issued a left turn heading 090. Air carrier X was issued a descent to FL290, to expedite through FL310. Air carrier X was asked his heading, replied 'heading 320'. Air carrier X was issued a left turn heading 270. The aircraft refused the heading. As air carrier Y target entered the j-ring (note: houston ARTCC now has a 6-MILE j-ring instead of the old 5-MILE ring). Air carrier X was asked to verify leaving FL310. Air carrier X reported leaving FL310 and reported the traffic in sight. The report leaving FL310 was received just as the quality assurance patch reported the event. I did not anticipate that an aircraft on an approximately 060 heading would turn 100 degree in a deviation, particularly since the only WX displayed was well to the south of the aircraft, and other aircraft had proceeded along the same route of flight with only minor deviations around higher tops. In retrospect the only thing I would possibly do differently is to limit the deviation of the aircraft to a specific amount of turn (something that I as a controller try not to do, because the aircraft crew has a much better view of the WX than I can obtain from the radar equipment). If the aircraft had told me he was going to turn to that degree, I would have changed his altitude sooner. Lesson learned, expect the unexpected when WX is involved, even if none is shown near the aircraft involved.

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Original NASA ASRS Text

Title: ACR WAS ALLOWED TO DEVIATE AROUND WX RESULTING IN LAST MINUTE ATC INTERVENTION TO MAINTAIN LEGAL SEPARATION WITH ANOTHER ACFT AT THE SAME ALT.

Narrative: I WAS THE RADAR CTLR AT THE HOUSTON ARTCC, LUFKIN SPECIALTY, ALEXANDRIA HIGH ALT SECTOR. THE MANUAL POSITION WAS COMBINED. APPROX 9 ACFT WERE ON FREQ. NUMEROUS TURBULENCE REPORTS (LIGHT TO MOD CHOP) WERE BEING MADE BY ACFT AT ALTS FROM FL250-FL350. NO WX WAS DEPICTED IN THE SECTOR EXCEPT FOR A SW-NE LINE OF HEAVY TSTMS FROM APPROX LCH..BTR..40 MI S OF MCB. THIS LINE WAS 80-100 MI S OF ALL ACFT IN THE SECTOR. AT THIS POINT I NOTICED FROM THE HISTORIES OF ACR X TRACK THAT THE ACFT HAD TURNED FROM AN APPROX 060 HDG TO NBND. I REALIZED THAT ON THAT HDG THERE WAS A POTENTIAL CONFLICTION WITH ACR Y, BUT THAT THE ACFT SHOULD PASS 10-15 MI LATERALLY. I PUT UP A 'J-RING' ON ACR X JUST TO BE SURE. AFTER TALKING TO ANOTHER ACFT I NOTED THAT THE HISTORIES OF ACR X TRACK NOW SHOWED HIM ON AN APPROX 330 HDG, PUTTING HIM HEAD ON WITH ACR Y (NOTE: THE COMPUTER GENERATED VECTOR LENGTH STILL SHOWED THE ACFT ON AN APPROX 020 HDG). ACR X WAS ISSUED A DSCNT TO FL310 AND TOLD TO EXPEDITE. THE ACFT STATED THAT WOULD 'PUT US RIGHT BACK INTO THIS STUFF'. ACR Y WAS ISSUED A LEFT TURN HDG 090. ACR X WAS ISSUED A DSCNT TO FL290, TO EXPEDITE THROUGH FL310. ACR X WAS ASKED HIS HDG, REPLIED 'HDG 320'. ACR X WAS ISSUED A LEFT TURN HDG 270. THE ACFT REFUSED THE HDG. AS ACR Y TARGET ENTERED THE J-RING (NOTE: HOUSTON ARTCC NOW HAS A 6-MILE J-RING INSTEAD OF THE OLD 5-MILE RING). ACR X WAS ASKED TO VERIFY LEAVING FL310. ACR X REPORTED LEAVING FL310 AND REPORTED THE TFC IN SIGHT. THE REPORT LEAVING FL310 WAS RECEIVED JUST AS THE QUALITY ASSURANCE PATCH REPORTED THE EVENT. I DID NOT ANTICIPATE THAT AN ACFT ON AN APPROX 060 HDG WOULD TURN 100 DEG IN A DEVIATION, PARTICULARLY SINCE THE ONLY WX DISPLAYED WAS WELL TO THE SOUTH OF THE ACFT, AND OTHER ACFT HAD PROCEEDED ALONG THE SAME ROUTE OF FLT WITH ONLY MINOR DEVIATIONS AROUND HIGHER TOPS. IN RETROSPECT THE ONLY THING I WOULD POSSIBLY DO DIFFERENTLY IS TO LIMIT THE DEVIATION OF THE ACFT TO A SPECIFIC AMOUNT OF TURN (SOMETHING THAT I AS A CTLR TRY NOT TO DO, BECAUSE THE ACFT CREW HAS A MUCH BETTER VIEW OF THE WX THAN I CAN OBTAIN FROM THE RADAR EQUIPMENT). IF THE ACFT HAD TOLD ME HE WAS GOING TO TURN TO THAT DEGREE, I WOULD HAVE CHANGED HIS ALT SOONER. LESSON LEARNED, EXPECT THE UNEXPECTED WHEN WX IS INVOLVED, EVEN IF NONE IS SHOWN NEAR THE ACFT INVOLVED.

Data retrieved from NASA's ASRS site as of August 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.