SW3 AND AN SMA HAVE NMAC BELOW DTW TCA.

Narrative

WE DEPARTED OFF RWY 21 WITH AN INITIAL CLRNC TO 4000 FT AND HDG 280 DEGS. TWR REQUESTED US TO KEEP THE TURN INSIDE OF THE PRECEDING DH8. WE HAD THE DH8 IN SIGHT AND COMPLIED. I CALLED FOR THE AFTER TKOF CHKLIST AND TWR TOLD US TO SWITCH TO DEP. THE CAPT MADE THE SWITCH AND WE HEARD DEP TELLING SOMEONE ABOUT TFC AT AN UNKNOWN ALT. WE THEN NOTICED THE DH8 TURNING TOWARDS US. I SLOWED THE CLB TO AVOID CONFLICT WITH THE DH8. THE CAPT MADE THE CALL TO DEP AND ADVISED HIM THAT WE HAD THE DH8 GOING OVER TOP AND HAD LEVELED AT 2000 FT. ATC TOLD US TO MAINTAIN 2000 FT. NEXT ATC ADVISED US OF TFC AT 11-12 O'CLOCK ALT UNKNOWN; NOT TALKING TO ANYONE; CLB AND MAINTAIN 3000 FT. WE STARTED THE CLB AND GOT THE TFC IN SIGHT. THE TFC WAS A SINGLE ENG LOW WING. AT 2300 FT WE WERE CONVERGING SO I PUSHED OVER TO DSND. THE ACFT PASSED OVER TOP OF US. AT THE CLOSEST POINT I WOULD SAY WE WERE WITH 250 FT VERT WHEN HE WENT OVER TOP OF US. WE ADVISED ATC OF THE DEV. HE ASKED US WHAT ALT THE ACFT WAS AT AND CLRED US TO 4000 FT. THIS SAME ACFT HAD BUSTED TOL AIRSPACE AND APPARENTLY HAD GOTTEN CLOSE TO SOME OTHER ACFT. WE CONTINUED ON TO OUR DEST WITHOUT FURTHER INCIDENT.