A CTR CTLR CLBED A B737 THROUGH AN OCCUPIED ALT RESULTING IN TCASII ALERT AND EVASIVE ACTION TAKEN BY BOTH ACFT.

Narrative

FLT FROM MCO TO BOS. WE WERE GIVEN A CLB CLRNC TO FL330 FROM FL290 BY ZJX JUST S OF CRG VOR ON A NBOUND HEADING. LEAVING FL296 WE RECEIVED A TA AND NOTED AN ACFT SBOUND AT FL310 HEADING IN OUR DIRECTION. BECAUSE OF THE EXTREME NOSE TO NOSE CLOSURE RATE THE TA BECAME AN RA WITH A MINIMUM CLB WARNING ON THE IVSI OF .5 OR 500 FPM. AT FL301 I FELT THAT THE 2 ACFT WOULD BE IN TOO CLOSE OF A PROX; DISCONNECTED THE AUTOPLT AND MADE AN EVASIVE MANEUVER 40 DEGS L WITH A 30 DEG BANK. FO SPOTTED THE CONFLICTING ACFT 4-5 MI OUT FROM OUR ACFT; THAT WAS TURNING L FROM US WITH THE BOTTOM OF HIS ACFT EXPOSED. I TOLD CTR OF OUR CONFLICT POTENTIAL NEAR MISS. CTLR RECLRED US TO FL290. CTLR CONFIRMED ACTUAL TFC CONFLICT ON CTR DISPLAY. NO PAX OR CREW MEMBERS WERE HARMED. CTR CLRED US BACK TO FL330. WE CONTINUED ON TO BOS WITHOUT FURTHER INCIDENT. THERE WERE 81 PAX AND CREW ON BOARD. GROSS WT WAS 106000 LBS. WX CONDITIONS CLR. SUPPLEMENTAL INFO FROM ACN 394264: DURING LEVEL FLT AT 31000 FT; OUR ACFT NARROWLY AVOIDED AN UNKNOWN ACFT. FIRST RECOGNIZED BY TCASII. WHEN VISUALLY SIGHTED; THE ACFT APPEARED AT OUR 12:30 O'CLOCK POS. AFTER OUR ACFT TOOK EVASIVE ACTION (A CLBING L TURN) THE UNKNOWN ACFT CLBED THROUGH OUR ORIGINAL FLT LEVEL (31000 FT).