ALTDEV ALT EXCURSION DURING FLC RESPONSE TO TCASII RA WITH OPPOSITE DIRECTION DSNDING TFC.

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LEVEL AT FL280 66 E OF CAPITAL VOR. TCASII ON 20 MI RANGE. THREAT ADVISORY ANNOUNCED AND INDICATED WITH CONFLICTING ACFT APPROX 20 MI DISTANT 1700 FT ABOVE US; DSNDING; 1 O'CLOCK POS. RA ANNOUNCED AND INDICATED WITH CONFLICTING ACFT 1100 FT ABOVE US; DSNDING; 1 O'CLOCK APPROX 12 MI. TCASII COMMANDED AN IMMEDIATE DSCNT WHICH WE EXECUTED. WE ALSO ADVISED KANSAS CITY OF OUR ACTIONS AND REASON. THE CTLR WHO HAD JUST ADVISED US OF THE TFC AS WE WERE EXECUTING OUR DEV; STATED THAT WE SHOULD DO WHAT WE NEED TO DO; BUT THAT THE CONFLICTING ACFT WAS NOW LEVEL AT 290. THIS WAS GOOD NEWS INDICATING THAT THERE WAS NO APPARENT DANGER OF CONTACT WITH THE OTHER ACFT; HOWEVER; WHAT IT ALSO INDICATED WAS THAT WE MAY HAVE BEEN DIRECTED TO EXECUTE AN UNNECESSARY ALTDEV BY THE TCASII. IN ANY EVENT WE LEVELED AT 27300 WITH THE SYS DECLARED A 'CLR OF CONFLICT;' AND THEN PROCEEDED TO CLB BACK TO 28000. THE CTLR STATED THAT WE HAD NOT VIOLATED ANYONE ELSE'S AIRSPACE; HOWEVER; HE DID HAVE TO CHANGE A CFT POS EARLIER THAN PLANNED BECAUSE OF A POTENTIAL CONFLICT SET UP BY OUR TCASII DSCNT.