B733 FLC INITIATES EVASIVE MANEUVER REACTING TO A TCASII RA AS BTV CTLR INSISTS THAT B733 FLC DSND AGAIN INTO CONFLICT WITH TCASII RA ACFT.

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WE WERE A REGULARLY SCHEDULED AIRLINE TRIP FROM BURLINGTON; VT; TO CHICAGO; IL (ORD). ACFT WAS B737-300 WITH TCASII AND FMS. WX WAS VFR AT ARPT WITH AN OVCST DECK 5000-8000 FT MSL. TKOF CLRNC WAS RWY 15 INCLUDED TURN R TO 190 DEG HDG CLB TO 10000 FT. AFTER TKOF DEP CTL GAVE US (X) TURN R DIRECT WATERTOWN VOR (ATR). WHILE IMC PASSING 8000 FT BURLINGTON DEP CTL TOLD US 'DSND TO 7000 FT.' JUST THEN OUR TCASII DISPLAYED ANOTHER ACFT (Y) TO OUR R BUT VERY CLOSE (WITHIN 4 MI). OUR RATE OF CLB (2000 FPM) TOOK US THROUGH 8000 FT TO APPROX 8300 FT. THE COPLT (PNF) ACKNOWLEDGE THE DSCNT INSTRUCTION BUT ASKED IF INSTRUCTIONS WERE STILL VALID SINCE WE WERE ABOVE 8000 FT. WE THEN GOT A TCASII PAINT OF INTRUDING ACFT (Y) AND A TA. AT 8200 FT WE BROKE OUT ON TOP OF CLOUDS IN VMC (VISIBILITY 20 MI). WE NEVER SAW THE OTHER ACFT. DEP SAID YES; THEY WANTED US BACK DOWN TO 7000 FT. WE DSNDED INTO CLOUDS TO 7000 FT AFTER VERIFYING TCASII DISPLAYED SEPARATION INCREASING. I (PF) OBTAINED A PHONE NUMBER AND NAME TO CONTACT TO DISCUSS EVENTS. AFTER LNDG CONTACT WITH BURLINGTON DEP CTL SUPVR VERIFIED EVENTS. HE SAID THE CTLR HAD BEEN FORTHCOMING AND A REVIEW OF THE TAPE; SHOWED VERT SEPARATION OF 500 FT AND 1.72 MI HORIZ. THE CTLR WHO WORKED THE EVENT WAS OFF THE SCOPE AND THAT THIS WAS A 'FLT EVENT.' PROB: CTLR LOST TRACK OF OTHER ACFT. ALTIMETER ENCODING CREATED A LAG ON HIS RADAR. HE NEGLECTED NOT HAVING KEPT US ABOVE 8000 FT.