NMAC.

Narrative

ARRIVING IAD; END OF 3 DAY TRIP. LOCATED 15 S OF DULLES; 090 DEGS ASSIGNED HDG; DSNDING THROUGH 4300 FT FOR 2000 FT. RECEIVED TCASII RA 'STOP DSCNT.' SCREEN DEPICTED TARGET AT OUR ALT; 12 O'CLOCK. LEVELED MOMENTARILY AT 4000 FT AND OBSERVED A RED CESSNA PASS OFF OUR L SIDE; OPPOSITE DIRECTION (4000 FT MSL; HDG 270 DEGS). DISTANCE ESTIMATED BTWN 300-500 FT. COPLT TOLD ME LATER WHEN HE LOOKED AT TCASII; TARGET WAS 300 FT BELOW US. I WAS HAND FLYING AT THE TIME. APCH INFORMED US THE FLOOR OF THE TCA AT THAT POINT WAS 2000 FT MSL. CESSNA WAS TRANSITIONING AT 4000 FT MSL; NOT TALKING TO DULLES. HE EVENTUALLY CONTACTED DULLES APCH AND LATER HE WAS TO CONTACT DULLES BY PHONE. NOTE: APPROX 2-3 MINS BEFORE INCIDENT; DULLES HAD CLRED US FOR A VISUAL APCH. ABOUT A MIN LATER HE CANCELED THAT CLRNC AND PUT US ON THE 090 DEG HDG AND GAVE US DSCNT TO 2000 FT. IN ESSENCE; APCH TURNED US DIRECTLY TOWARDS THE CONFLICT (UNINTENTIONALLY). IF WE HAD CONTINUED WITH THE VISUAL APCH; I.E.; PROCEEDING DIRECTLY TO THE FIELD; THE CESSNA WOULD NOT HAVE BEEN A CONFLICT.