FLC OF DC9-50 IS VECTORED FOR L DOWNWIND ON INITIAL CLB AND HAS TCASII ACTIVATE WHEN CLRED TO CLB. A LIGHT TWIN ACFT HAS TURNED AND IS 200 FT ABOVE THEM.

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ON A VECTORED L DOWNWIND DEP FROM RWY 30L MSP; LIGHT TWIN TFC WAS POINTED OUT FLYING SBOUND AT 3500 FT. WE WERE TOLD TO LEVEL OFF AT 3000 FT (NORMALLY WE'RE GIVEN 5000 FT INITIALLY). BOTH OF US SAW THE TFC. WE WERE GIVEN A HDG TO 200 DEGS WHICH PUT THE TWIN AT OUR 12:30 O'CLOCK POS. WE WERE TOLD THAT THE TWIN WAS GOING TO TURN L TO NE; BUT THEN ATC CLRED US TO CLB. JUST AS I (PF) ADDED CLB PWR AND COMMENCED THE CLB; THE TWIN ABRUPTLY ROLLED INTO AT LEAST A 60 DEG (PROBABLY GREATER) L TURN IN FRONT AND JUST ABOVE US. WE DID GET A TCASII RA. I LEVELED AT 3300 FT AND HAD TO TURN R (SW) TO PASS BEHIND HIM. TWIN WAS APPARENTLY ON ANOTHER TWR FREQ AND DID NOT KNOW OF US (PER PHONE CALL TO TRACON LATER). TWIN WAS DOING SOME PHOTO SURVEYING -- WE WERE TOLD. THIS WAS VERY CLOSE TO A NEAR MISS; IN MY OPINION; BECAUSE OF OUR SPD AND CLOSING RATE ON THE TWIN. TRACON APOLOGIZED IN SUBSEQUENT PHONE CALL. THIS WAS TOO CLOSE OF A CALL IN CLASS B AIRSPACE. ATC DID NOT KNOW THE TWIN WAS GOING TO TURN SO ABRUPTLY IN FRONT OF US; BUT WE SHOULD NOT HAVE BEEN GIVEN A CLB WITH HIM IN FRONT OF AND ABOVE US.