LTSS AND NMAC OCCURRED BTWN A C340 AND A BE99 WHEN APPROPRIATE IFR SEPARATION WAS NOT APPLIED BY THE APCH CTLR. FREQ CHANGE WAS NOT IN ACCORDANCE WITH INTERFAC LOA.

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PERTINENT BACKGND: IN LATE FEB/96; CYX APCH CTL WAS ASSUMED BY WYOMING AIR NATL GUARD. OLD FAA APCH WAS NON RADAR; NEW WANG APCH EQUIPPED WITH KOREAN WAR ERA RADAR. AT XX32 LCL; APCH INFORMED ME OF 2 IFR INBOUNDS. FIRST; A C340 FROM THE W. SECOND; A BE99 FROM THE NW. ANOTHER ACFT; A BE90; WAS ON MY FREQ INBOUND VFR FROM THE S. AT XX36 THE C340 MADE INITIAL CALL ON TWR FREQ; AND I ASSIGNED HIM R DOWNWIND ENTRY RWY 26; THE ONLY RWY IN USE. APCH CTLR WAS ADVISED OF THE C340'S INSTRUCTIONS; SO THEY COULD USE THAT INFO REF THE BE99. BOTH IFR'S WERE TO BE ON VISUAL APCH TO RWY 26. THE BE90 REQUESTED AND WAS ASSIGNED L BASE ENTRY; WITH ADDITIONAL INSTRUCTIONS TO FOLLOW THE BE99; WHO WAS ON MIDFIELD R DOWNWIND. THEN APCH CALLED TO ADVISE ME THAT THE BE99 WAS 7 MI E; 'COMING TO YOU.' HE THEN ASKED IF THE C340 WAS ON SHORT FINAL RWY 26. I REPLIED IN THE NEGATIVE; THAT THE C340 WAS ON HIS BASE LEG. AT THIS TIME; THE BE90 AND THE C340 BEGAN EXCHANGING TFC INFO ON TWR FREQ; SO I HAD TO HANG UP ON APCH CTL. THE BE90 GETS THE C340 IN SIGHT AND I REISSUED HIS #2 SEQUENCING. ALL THIS; FROM THE BE90'S BASE ENTRY REQUEST TO HIS VISUAL CONTACT WITH THE C340; OCCURRED FROM XX38 TO XX40. AT XX40; THE BE90 ADVISED HE HAD 2 ACFT IN SIGHT AHEAD OF HIM. I LOOKED IN THE DIRECTION OF FINAL AND SAW THE BE99 IN VERY CLOSE PROX TO THE C340. I MADE 2 XMISSIONS IN THE BLIND TO THE BE99 WHO DID NOT REPLY; BUT DURING THE SECOND DID SUDDENLY MAKE A SHARP L TURN; CONTINUING SE. THE C340 LANDED WITHOUT FURTHER INCIDENT AT XX42; FOLLOWED SHORTLY THEREAFTER BY THE BE90. THE BE99 FINALLY MADE RADIO CONTACT AT XX41; AND LANDED AT XX45. ALL 3 ACFT WERE ASKING WHAT WAS GOING ON. THE INCIDENT HAS BEEN REFERRED TO THE WYOMING AIR NATL GUARD FOR INVESTIGATION. IT IS OUR FIRM BELIEF THAT WANG CTLRS VIOLATED RADAR SEPARATION STANDARDS BTWN VISUAL APCHS AND OUR LOA BTWN CYS TWR AND WANG APCH. THEY SENT ME 2 VISUAL APCH ACFT WITHOUT SEPARATION; VISUAL OR OTHERWISE. THEY ARE SUPPOSED TO XFER COMS ON INBOUND IFR ACFT NO LATER THAN 8 MI FROM THE ARPT; AND RECEIVE APPROVAL TO HOLD ON TO ANY IFR ARR PAST THAT POINT. THEY VIOLATED BOTH OF THOSE LOA PROVISIONS WHEN THEY CLRED THE BE99 FOR A VISUAL APCH 7 MI FROM THE ARPT. THEY ISSUED CTL INSTRUCTIONS TO THE BE99 IN MY AREA OF CTL THAT COULD HAVE CAUSED AN ADDITIONAL CONFLICT WITH THE BE90 (THE SHARP L TURN WAS IN RESPONSE TO A WANG CTL INSTRUCTION).