A CLBING ACR B737 TOOK EVASIVE ACTION DSND; TURN TO AVOID A BONANZA IN THE PHL TFC PATTERN.

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WE WERE IN POS FOR TKOF ON RWY 27L AT PHL IN AN ACR B737- 200. BEFORE TKOF CLRNC WAS ISSUED; THE TWR CTLR ISSUED A DEP HDG OF 260 DEGS. NORMAL DEP HDG ON THE SID IS 255 DEGS. ONCE CLRED FOR TKOF; WE WERE CONTACTED BY THE TWR AND TOLD TO FLY A HDG OF 255 DEGS. A FEW SECONDS LATER WE WERE GIVEN A HDG OF 270 DEGS BY THE TWR 'FOR TFC.' TWR CTLR DID NOT SPECIFY WHERE THE TFC WAS IN RELATION TO OUR POS. WE WERE AT 800 FT ON THE DEP PATH FOR RWY 27L. IMMEDIATELY THEREAFTER WE RECEIVED AN AURAL AND VISUAL TCASII RA TO 'DSND.' SIMULTANEOUSLY THE FO CALLED TFC AT 10 O'CLOCK; 200 FT CLOSING. WE IMMEDIATELY MADE A R DSNDING TURN OF 60 DEGS BANK AND -5 DEGS PITCH TO A HDG OF 340 DEGS; DSNDING BACK TO 800 FT FROM 1100 FT; MISSING A BONANZA BY 200 FT. CTLR WAS QUERIED BUT HAD NO EXPLANATION. UPON LNDG; WE CALLED PHL TWR SUPVR AND LEARNED THAT TRACON WAS TALKING TO THE BONANZA WHILE HE WAS IN THE TWR'S AIRSPACE AND THAT THE BONANZA PLT HAD RPTED EARLIER THAT HE HAD BECOME DISORIENTED IN RELATION TO PHL ARPT. THERE WERE NO INJURIES OR ACFT DAMAGE.