POTENTIAL CONFLTIC BETWEEN 2 ACR ACFT.

Narrative

INBND TO DCA; WASH APCH ADVISED DEPART AML 070 DEGS HDG. AFTER AML CLRED TO 4000'; LEFT TURN TO 030 DEG 'VECTOR FOR INBND TFC 6 MI E OF CABIN JOHN.' NEXT COMMAND; RIGHT TURN 140 DEGS. THE NEXT HDG; I BELIEVE; WAS RIGHT TO 230 DEGS; AT LEAST A SW HDG; DSND TO 3000'. WE HAD STILL NOT LEVELED AT 4000' AND DSNDING THROUGH 4400' I SAW LGT ACR Y PASS LEFT TO RIGHT IN FRONT OF US (ABOUT A 70 DEG CROSS AT APPROX 3000' AND AT ABOUT 3/4 MI). I CALLED THIS TO APCH CTLR AND WE WERE TOLD TO LEVEL 4000'. WE WERE NEVER ADVISED OF ANOTHER ACFT IN THE AREA. I IMMEDIATELY QUESTIONED THE CTLR AND WAS ADVISED THE ACFT WAS UNDER THE CTL OF ANOTHER CTLR. I CALLED ON THE GND AND TALKED TO RAPCON SUPVR. HE INFORMED ME OF THE FOLLOWING. 1) ACFT UNDER SEPARATE CTLRS WERE BEING VECTORED TO CABIN JOHN BRIDGE TO COMMENCE A RIVER VISUAL APCH RWY 18. 2) ACR Y FAILED TO MAKE THE TURN ON TO THE RIVER. 3) MY CTLR WAS NOT AWARE OF THE IMPENDING CONFLICT. 4) THERE WAS NO PROB SINCE WE LEVELED OFF AT 4000'. 5) THIS PROC HAS WORKED FOR YRS AND IS 'THE BEST THAT IS AVAILABLE.' OPINION: THIS TYPE OF INCIDENT AT WASH NATL IS CREATED BY AN OVERZEALOUS DESIRE FOR NOISE ABATEMENT AND DESIRE FOR MAX FREQ OF OPS. A WHOLE LOT OF PEOPLE WILL EVENTUALLY GET KILLED IF THESE POLICIES REMAIN IN EFFECT.