AN LGT ACR HAD LTSS WITH ANOTHER UNSPECIFIED ACFT AFTER TKOF NAVING ON A SID. POTENTIAL CONFLICT.

Narrative

WE WERE DEPARTING SEATTLE FOR DULLES ON FLT X. DISCUSSION WAS HELD AT THE GATE BTWN ME AND THE FO ON HOW BEST TO PROGRAM THE DEP IN THE CDU. WE DECIDED TO PROGRAM THE LATITUDE AND LONGITUDE OF THE TURN POINT FOR DEPS FROM RWY 16 IN THE CDU AND USE LNAV AFTER TKOF TO DIRECT US TO THE TURNING POINT AND THEN HDG SELECT FOR THE REQUIRED TURN TO 070 DEGS. TKOF WAS UNEVENTFUL FROM RWY 16R AND THE FO CALLED FOR AND I INITIATED LNAV AND VNAV AT THE PROPER POINTS. AT THE TURN POINT; THE FO CALLED FOR AND WAS GIVEN HDG SELECT TO A HDG OF 070 DEGS. AS WE ENTERED THE TURN; I OBSERVED AN ACFT AT 10 O'CLOCK TO OUR POS AND SLIGHTLY BELOW US ALSO IN A L TURN. I POINTED OUT THE TFC TO THE FO AND HE SHALLOWED OUT HIS BANK. I THEN CALLED DEP CTL AND INQUIRED ABOUT THE OTHER ACFT. DEP GAVE US A HDG OF 100 DEGS AND THE DEP WAS COMPLETED UNEVENTFULLY. WE WERE AT ALL TIMES ABOVE AND OUTSIDE THE TURN OF THE OTHER ACFT. POSSIBLY THIS DEP COULD BETTER BE FLOWN IN THE VOR MODE; HOWEVER THE CDU AND PRESENT POS WERE CHKED PER SOP PRIOR TO ENG START AND SOP WAS FOLLOWED DURING THE DEP.