ALTDEV ALT EXCURSION AFTER RECEIVING TCASII TA.

Narrative

WHILE FLYING AT AN ALT OF 8000 FT; APPROX 5 MI N OF MADISON VOR; GOING DIRECT TO MADISON VOR; BRADLEY APCH RPTED A LIGHT ACFT AT 11 O'CLOCK AND 2 MI; 8500 FT. THERE WAS A CUMULUS BUILDUP BTWN US AND THE CONFLICTING TFC. WE OBSERVED THE ACFT ON TCASII; HOWEVER; OUR TCASII SYS ARE CURRENTLY NOT AUTHORIZED FOR RA; THUS; NO RA'S WERE GIVEN BY THE TCASII. THE OTHER ACFT THEN STARTED A DSCNT DOWN TO 8300 FT AND CONTINUED ITS DSCNT AND SW COURSE ACROSS OUR FLT PATH. BRADLEY CTLR CALLED THE OTHER ACFT TWICE; THE SECOND TIME VERY FRANTICALLY. THE CTLR THEN TOLD US THE TFC WASN'T ANSWERING HIM. WE WERE LOOKING FOR HIM WHEN AT THE LAST MIN MY FO SAW HIM AND POINTED TO OUR 10 O'CLOCK POS. OUT OF MY PERIPHERY I SAW AN ACFT HDG FOR US. I PULLED THE ACFT UP TO 8500 FT AND AVOIDED A COLLISION. THE ABRUPT MANEUVER RESULTED IN A FLT ATTENDANT FALLING DOWN IN THE GALLEY AREA; SEVERELY INJURING HER ANKLE. THE LIGHT ACFT PASSED IMMEDIATELY BEHIND US AND CONTINUED ON ITS WAY; VFR. BRADLEY ATC WAS NOTIFIED OF MY INTENT TO FILE A NEAR MISS RPT. HAVING A FULLY OPERATIONAL TCASII WOULD CERTAINLY HAVE HELPED IN THIS EVENT. IT WOULD HAVE GIVEN US AN RA MUCH SOONER AND AVOIDED THE ABRUPT MANEUVER. WE NEVER SAW THE LIGHT ACFT UNTIL HE CAME AROUND FROM BEHIND THE BUILDUP. ALSO; THE FRANTIC CHATTER ON THE RADIO WAS DISTRACTING TO SAY THE LEAST AND INHIBITED US FROM CALLING THE CTLR TO GET MORE INFO FROM HIM. THE VFR ACFT LATER SAID HE HAD US IN VISUAL CONTACT BUT COULDN'T SAY SO BECAUSE HE COULDN'T XMIT DUE TO THE CTLR CONSTANTLY TALKING. THAT; HOWEVER; DOESN'T EXCUSE THE VFR ACFT FROM STRAYING FROM HIS VFR CRUISING ALT.