ACR MAKES GAR AND CONFLICTS WITH A COMMUTER ACFT ALSO MAKING A GAR ON AN INTERSECTING RWY.

Narrative

I WAS PERFORMING AS CAPT ON A FLT FROM PIT TO PHL. APCH CTL HAD VECTORED US FOR A VISUAL APCH TO RWY 27R. AT APPROX 9 NM FROM THE ARPT; WE WERE INSTRUCTED TO 'SQUARE YOUR TURN TO FINAL; CLRED VISUAL APCH TO RWY 27R.' WE COMPLIED AND WERE SUBSEQUENTLY TRANSFERRED TO TWR. WE ADVISED TWR THAT WE WERE ON A 7 MI FINAL. TWR TOLD US TO SLOW TO OUR FINAL APCH SPD AND THAT WE WERE #2 BEHIND AN LTT Z. SIMULTANEOUSLY; THE TWR WAS CTLING A COMMUTER FLT THAT WAS APCHING RWY 35 (WHICH INTERSECTS RWY 27R AT ABOUT 2000 FT FROM THE APCH END). AT APPROX 2 1/2 NM FROM THE RWY; WE OBSERVED THE LTT TOUCHING DOWN ON RWY 27R. WE CONTINUED AND FOCUSED OUR ATTN ON THE LTT. TWR CLRED US TO LAND; HOWEVER AT ABOUT 200 FT AGL ON SHORT FINAL; IT APPEARED THAT THE LTT WOULD NOT CLR THE RWY PRIOR TO OUR TOUCHDOWN AND WE AGREED A GAR WAS WARRANTED. AT THE SAME TIME; TWR DECIDED THE COMMUTER WOULD NOT HAVE ADEQUATE SEPARATION FROM OUR ACFT AND INSTRUCTED THAT ACFT TO GAR. WE BEGAN OUR GAR STRAIGHT AHEAD AND ADVISED TWR OF OUR ACTION. TWR ADVISED THE COMMUTER ACFT OF OUR GAR. AT THAT MOMENT; WE OBSERVED THE COMMUTER TO OUR PORT SIDE IN APPROX A 45 DEG BANKED L TURN AT OUR ALT (APPROX 200-300 FT) AND ABOUT 600 FT LATERALLY FROM US. WE BOTH SUBSEQUENTLY REENTERED VFR PATTERNS AND LANDED ON OUR ORIGINALLY PLANNED RWYS. I FEEL THE PRIMARY RESPONSIBILITY FOR THIS OCCURRENCE LIES WITH THE TWR CTLR IN THAT HE DELAYED HIS DECISION TO PROVIDE SEPARATION SO LONG AS TO CAUSE A POTENTIAL DISASTER. ADDITIONALLY; WE SHOULD HAVE BEEN ADVISED OF THE COMMUTER'S POS SO THAT WE COULD HAVE MADE OUR OWN DETERMINATION AS TO POTENTIAL CONFLICT AND WOULD HAVE BEEN IN A POS TO ENSURE OUR OWN SEPARATION.