ACR X DEVIATING AROUND WX HAD LTSS FROM ACR Y. SYS ERROR.

Narrative

ACR X MAKES INITIAL CONTACT WITH ZID. RPTS LEVEL AT FL330 AND SAYS 'DEVIATING E.' CTLR SAYS ROGER. ACR X LIGHT PLANE SHOWS DFW.1.LIT.J131.PXV..VHP..FWA.1.DTW DIRECT. HE IS ROUGHLY 30 MI SE OF COURSE AND STILL DIVERGING FROM THE LIT TO PXV LEG BY APPROX 20 DEGS. MEMPHIS CTR HAD NOT COORDINATED THE DEV WITH US; SO WE WERE UNAWARE OF HOW HE HAD BEEN CLRED TO DEVIATE. SEVERE TSTMS WERE IN THE NORTHERN PORTION OF THE SECTOR AS PART OF A LINE STRETCHING W/E APPROX STL..CVG. 2 GAPS WERE PRESENT IN THE WX; 1 OVER THE SAM VOR; THE OTHER OVER THE OOM VOR. TSTM LINE WAS SEVERE WITH TOPS IN EXCESS OF FL410. ACR Y MAKES INITIAL CONTACT WITH ZID. RPTS LEVEL AT FL330 AND REQUESTS FL290. CTLR ACKNOWLEDGED CALLUP AND TELLS ACR Y THAT HE WILL HAVE FL290 IN ABOUT A MIN. IS ON HIS FLT PLAN WHICH SHOWS FROM POINTS SW OF PXV; LEX AND CVG. THIS WAS AN ALTERNATE ROUTING PUT OUT DUE TO SEVERE WX OVER THE ABB ARR GATE TO CVG. ACR Y WAS ROUGHLY AT ACR X 7 O'CLOCK POS; 8 MI; SAME HDG; SAME SPD. WHEN ACR Y CROSSED THE COMMON BOUNDARY HE WAS ISSUED FL290. LESS THAN A MIN LATER BOTH D-SIDE AND R-SIDE WERE ALERTED TO THE LOSS OF SEPARATION BTWN ACR X AND ACR Y WHEN SIMULTANEOUSLY CONFLICT ALERT AND ADEP WENT OFF. ACR X HAD BEGUN A STEEP TURN TO THE L WITHOUT ALERTING THE CTLRS. THE 8 MI IN TRAIL QUICKLY ERODED AS ACR X TURNED NEARLY 90 DEGS L IN 1 MIN. WHEN QUESTIONED AS TO HIS ACTION; ACR X SAID THAT HE WAS TRYING TO FIND VHP AND GO DIRECTLY TO IT. ACR X TURN WAS IN EXCESS OF 30 DEGS TOO FAR TO THE W FOR PXV. THE CTLR HAD ONLY BEEN ON POS 7 MINS WHEN THE ERROR OCCURRED. PREVENTION: ACFT SHOULD BE REQUIRED TO ALERT CTLRS PRIOR TO MAKING TURNS IN EXCESS OF 10 DEGS AFTER HAVING BEEN ESTABLISHED ON A HDG FOR DEVS. THIS WOULD ELIMINATE THE VERBAGE 'ADVISE THE CTLR WHEN YOU ARE READY TO TURN BACK ON COURSE.' IT WOULD PREVENT DEVIATING ACFT FROM CHANGING COURSE SEVERAL TIMES WHILE DEVIATING WITHOUT ATC'S ACKNOWLEDGEMENT. CURRENTLY; POSITIVE CTL NEAR SEVERE WX REQUIRES EITHER ALL ALT SEPARATION (WHICH IS NOT USUALLY PRACTICABLE) OR LOTS OF EXCESS VERBAGE (WHICH IS ALREADY AT A PREMIUM).