AN ACR FLC EXPERIENCED A TRACK ERROR NOTING THAT TWO SIMILAR SOUNDING WAYPOINTS; VINSE AND BINNS; ARE WITHIN 30 NM OF EACH OTHER AND MAY BE EASILY CONFUSED.

Narrative

WHILE ENROUTE AT CRUISE; ATC CLEARED US TO A FIX THAT WAS NOT ON OUR CURRENT ROUTE; THEN DIRECT AIR (WHICH WAS ALONG OUR FILED ROUTE). THE CAPTAIN READ BACK THE FIX NAME PHONETICALLY AS 'BINNS' AND TYPED IT IN THE FMC. IT APPEARED IN FRONT OF US; WITH A 10 DEGREE TURN TO THE LEFT; AND ABOUT 40 MILES AWAY. AFTER CHECKING WITH ME; HE EXECUTED THE WAYPOINT. AFTER A COUPLE MINUTES; ATC ASKED US FOR OUR HEADING. THE CAPTAIN SAID WE ARE DIRECT BINNS; TO WHICH ATC REPLIED; 'NOT BINNS; YOU'RE SUPPOSED TO GO DIRECT VINSE.' WE HAD HIM SPELL IT TWICE; THEN TYPED VINSE IN THE FMC. IT TURNS OUT THAT THE TWO FIXES ARE ABOUT 30 MILES APART. WE CORRECTED OUR HEADING ABOUT 30 DEGREES TO THE RIGHT AND PROCEEDED DIRECT. THE FIXES ARE VERY SIMILAR PHONETICALLY AND SOUND NEARLY IDENTICAL WHEN SPOKEN. WE DID READ BACK THE FIX ORIGINALLY; BUT I DO REMEMBER SOME UNCERTAINTY IF 'BINNS' WAS CORRECT. BUT WHEN ATC DID NOT CORRECT US IMMEDIATELY; AND THE FIX APPEARED TO BE ALONG THE RIGHT PATH; EVERYTHING SEEMED OK. ATC DID NOT ACT OVERLY CONCERNED AND WE DO NOT KNOW OF ANY TRAFFIC CONFLICT. HOWEVER; FURTHER QUERY OF THE PHONETIC SPELLING OF VINSE WOULD HAVE PREVENTED THIS ERROR.