BTV CTLR RECOGNIZES THAT F16 FLT TURNS CONTRARY TO INSTRUCTIONS AND COMES INTO CONFLICT WITH B190 DEPARTING FROM ANOTHER RWY; ISSUING ALTERNATE CTL INSTRUCTIONS.

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A FLT OF 3 F16'S (X) WERE PROCEEDING STRAIGHT IN TO RWY 15 FOR AN OVERHEAD APCH; L BREAK; 1800 FT BREAK ALT. THERE WAS A B1900 (Y) COMMUTER THAT DEPARTED RWY 19 ON RWY HDG. THIS ACFT WAS TURNED R HDG 320 DEGS AND LEVEL 2000 FT ABOUT 3 MI SW OF THE ARPT. THE F16'S DID NOT BREAK L BUT TURNED W. THEY WERE ABOUT 1 MI W OF THE FIELD WHEN THEY ADVISED THEY COULDN'T BREAK L BECAUSE OF A CLOUD. THEY WERE HEADED DIRECTLY AT THE B1900 AND I GAVE THEM AN IMMEDIATE TURN AND CLB TO GET AWAY FROM THE COMMUTER. WE SPOKE WITH THE F16 FLT LEADER LATER AND ADVISED HE CAN'T JUST BREAK OFF HIS APCH AND TURN ANY WAY HE WANTS WITHOUT TELLING US. AT 350 KTS; IF HE TURNS IN AN UNEXPECTED DIRECTION; IT MAY CAUSE CONFLICTS VERY QUICKLY. THE PLT SAYS THAT HE TURNED R OUT OF THE PATTERN BECAUSE HE THOUGHT IT WAS MORE IMPORTANT TO STAY CLR OF CLOUD. HE SAID THE WX WAS BETTER TO THE W. SUPPLEMENTAL INFO FROM ACN 456021: WX AT BTV RPTED AS 6000 FT BROKEN AND 6 MI VISIBILITY. CLRED FOR A VISUAL APCH TO RWY 15 AT BTV. SOMEWHERE BTWN 1-3 MI OFF OF THE APCH END AT 1800 FT MSL (GOING TO INITIAL) IT BECAME APPARENT THAT THE BREAK COULD NOT BE ACCOMPLISHED DUE TO A CLOUD DIRECTLY OVER THE FIELD AND E OF THE FIELD. WHILE DEVIATING TO THE W SLIGHTLY TO MAINTAIN CLR OF CLOUDS; A XMISSION TO TWR WAS MADE TO INFORM THAT THE OVERHEAD PATTERN COULD NOT BE ACCOMPLISHED; AND REQUESTED VECTORS BACK TO RADAR. TWR GAVE AN IMMEDIATE L TURN TO 360 DEGS AND CLB TO 3000 FT. A COMMUTER B1900 RPTEDLY HAD TO REACT TO TCASII ADVISORIES AS WE DEVIATED 1/2 MI W AROUND THE CLOUD. TWR RPTS ALSO THAT LEGAL SEPARATION WAS MAINTAINED AND NO VISUAL CONTACT WAS ESTABLISHED BTWN THE ACFT. MY COMMENTS: THE ATIS HAD NOT UPDATED PROPERLY. ACTUAL CONDITIONS OVERHEAD WERE ACTUALLY 2000 FT AND 3 MI. I WOULD NOT HAVE ATTEMPTED AN OVERHEAD IF ATIS WAS CLOSE TO ACTUAL CONDITIONS. I QUESTION TCASII PRECISION IN A MANEUVERING ENVIRONMENT. THE B1900 HAD JUST DEPARTED RWY 19 AND TURNED R TO 320 DEGS. I DON'T THINK WE WERE REALLY A CONFLICT.