Narrative:

I was working departure control. Air carrier X was being vectored on downwind by arrival control at 5000 ft. I was working air carrier Y climbing wbound to 4000 ft when the 2 aircraft targets came apart, I climbed my aircraft Y to 10000 ft on a 40 degree diverging course. Air carrier X suddenly and without warning started turning right from assigned heading 230. The arrival controller noticed first as now air carrier X was turning toward my aircraft Y which was not out of 4500 in the climb. After action was taken to gain separation the arrival controller questioned air carrier X. The response was that he was responding to a TCAS alert on a 1200 code with no altitude. At the time there was no traffic observed on the scope within 10 mi of air carrier X with the exception of my air carrier Y. I feel that the pilot should have at least let ATC know as soon as possible that he is intending to deviate from ATC instructions. I also feel that there is something really wrong with TCAS or the pilot's interpreting the data received from TCAS. In either case, the only traffic in the vicinity being my air carrier Y. Air carrier X was turned to the worst possible place and done so when good separation existed and not even the remotest possibility of collision existed. If I and the arrival controller were very busy at the time and had not noticed the discrepancy, it could have turned out a lot worse.

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Original NASA ASRS Text

Title: ACR REACTING TO TCAS PRESENTATION MADE UNAUTHORIZED HDG CHANGE WHICH CAUSED LTSS WITH ANOTHER ACR. PLT DEV.

Narrative: I WAS WORKING DEP CTL. ACR X WAS BEING VECTORED ON DOWNWIND BY ARR CTL AT 5000 FT. I WAS WORKING ACR Y CLBING WBOUND TO 4000 FT WHEN THE 2 ACFT TARGETS CAME APART, I CLBED MY ACFT Y TO 10000 FT ON A 40 DEG DIVERGING COURSE. ACR X SUDDENLY AND WITHOUT WARNING STARTED TURNING R FROM ASSIGNED HDG 230. THE ARR CTLR NOTICED FIRST AS NOW ACR X WAS TURNING TOWARD MY ACFT Y WHICH WAS NOT OUT OF 4500 IN THE CLB. AFTER ACTION WAS TAKEN TO GAIN SEPARATION THE ARR CTLR QUESTIONED ACR X. THE RESPONSE WAS THAT HE WAS RESPONDING TO A TCAS ALERT ON A 1200 CODE WITH NO ALT. AT THE TIME THERE WAS NO TFC OBSERVED ON THE SCOPE WITHIN 10 MI OF ACR X WITH THE EXCEPTION OF MY ACR Y. I FEEL THAT THE PLT SHOULD HAVE AT LEAST LET ATC KNOW ASAP THAT HE IS INTENDING TO DEVIATE FROM ATC INSTRUCTIONS. I ALSO FEEL THAT THERE IS SOMETHING REALLY WRONG WITH TCAS OR THE PLT'S INTERPRETING THE DATA RECEIVED FROM TCAS. IN EITHER CASE, THE ONLY TFC IN THE VICINITY BEING MY ACR Y. ACR X WAS TURNED TO THE WORST POSSIBLE PLACE AND DONE SO WHEN GOOD SEPARATION EXISTED AND NOT EVEN THE REMOTEST POSSIBILITY OF COLLISION EXISTED. IF I AND THE ARR CTLR WERE VERY BUSY AT THE TIME AND HAD NOT NOTICED THE DISCREPANCY, IT COULD HAVE TURNED OUT A LOT WORSE.

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.