ACR X HAD CONFLICT ACFT Y.

Narrative

ACR X APCHED ALLENTOWN FROM THE SW AND WAS VECTORED TO A R DOWNWIND TO RWY 24. ALLENTOWN APCH CALLED THE FIELD AT OUR 1:30-2:00 POS AT 4-5 MI AND QUESTIONED WHETHER WE HAD THE FIELD VISUALLY. I TOLD APCH THAT THE FLT VISIBILITY WAS 2-3 MI AT BEST AND WE DID NOT HAVE THE FIELD IN SIGHT. APCH THEN VECTORED US FOR THE LOC BACK-COURSE TO RWY 24. WE WERE TOLD TO DSND TO 1800 FT AND WERE GIVEN A TIGHT R TURN TO INTERCEPT THE BACK-COURSE. THE FO WAS CTLING THE ACFT THROUGH THE AUTOPLT AND WAS SLOW TO MAKE THE INTERCEPT; SLOW TO SLOW THE ACFT TO APCH SPD AND CONFIGURE FOR THE LNDG. WE WERE CLRED FOR THE APCH AND TOLD TO CONTACT THE TWR. AS WE CAME OVER TO TWR FREQ; I HEARD THE TWR CLR A CESSNA FOR TKOF. AT THIS POINT WE WERE JUST INSIDE 'WILEY' FINAL APCH FIX AND APPROX 3-4 MI FROM THE RWY. WE WERE 'CLRED TO LAND.' THE RWY WAS NOT IN SIGHT AT THIS POINT AND THE FO WAS NOW HAND FLYING THE ACFT AND SLOWING. I AGAIN HEARD THE TWR CLR A CESSNA FOR TKOF AND SHORTLY THEREAFTER STARTED TO DIMLY PICK UP THE RWY THROUGH THE HAZE. AS THE FIELD BECAME MORE CLRLY VISIBLE; I OBSERVED A CESSNA ON TKOF LEG TURNING R XWIND. AT THIS POINT OUR ACFT WAS ROUGHLY 1-1 1/2 MI FROM THE THRESHOLD AND ABOUT 400-500 FT AGL. AGAIN TWR CLRED A CESSNA FOR TKOF. SHORTLY THEREAFTER; I OBSERVED ANOTHER CESSNA MOVING DOWN THE RWY ON TKOF. I DID NOT OBSERVE THIS ACFT UNTIL I DETECTED HIS MOVEMENT DOWN THE RWY. MY FIRST IMPRESSION WAS THAT SPACING WOULD NOT BE ADEQUATE. I CALLED THE TFC OUT TO THE FO BUT HE DID NOT CLRLY RESPOND OR INDICATE THAT HE HAD THE CESSNA ON TKOF ROLL IN SIGHT. THE CESSNA WAS AIRBORNE QUICKLY HOWEVER AND IT MOMENTARILY APPEARED THAT THERE WOULD BE NO RWY CONFLICT. THE CESSNA HOWEVER WAS CLBING VERY; VERY SLOWLY AND WAS MAINTAINING RWY HDG. HIS SLOW SPD AND FLT PATH COMBINED WITH OUR CLOSURE OF OVER 100 KTS INDICATED TO ME THAT SPACING WOULD BE MINIMAL AND THAT ON OUR LNDG ROLLOUT; WE MIGHT ACTUALLY PASS UNDERNEATH HIM. TWR RECOGNIZED THE CONFLICT AND TOLD THE CESSNA TO BEGIN AN IMMEDIATE R TURN. THE CESSNA SLOWLY COMPLIED. WE CONTINUED THE APCH AND LANDED. ON OUR LNDG ROLL-OUT; THE CESSNA PASSED OFF OUR R WING APPROX 150-200 FT LATERALLY AT AN ALT OF 100- 150 FT.