ACR MAKES WRONG TURN ON DEP FROM FOREIGN ARPT.

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DEP WAS FULLY BRIEFED AND WE WERE SET TO GO ON RWY 27 WITH THE DEP IN THE FMC. I (FO) WAS FLYING AND THE TRIANGLE WAS PERFECTLY IN PLACE TOUCHING THE RWY. IT WAS BRIEFED I WOULD FLY USING THE MAP MODE AND LNAV AND THE CAPT WOULD BACK ME UP ON RAW DATA DISPLAYED ON HIS HSI. AFTER PASSING APPROX 800-900 FT MSL OVER THE VOR ON THE DEP (LOCATED JUST OFF THE DEP END); THE FLT DIRECTOR COMMANDED A L TURN. I THOUGHT IT WOULD BE A SMALL CORRECTION; BUT I FOLLOWED IT FOR APPROX 15-20 DEGS UNTIL THE CAPT HAD A VOR COURSE LOCK-ON AGAIN AND IT SHOWED THE COURSE OFF TO THE R. AT THAT TIME I WAS TURNING BACK TO THE COURSE WHEN ATC SAID FLY HDG 280 DEGS TO GET BACK TOWARDS THE COURSE. REMAINDER OF SID FLOWN IN ACCORDANCE WITH SID SPECS. LNAV FLT COMMANDS TOOK PLACE DIRECTLY OVERHEAD DURING VOR STATION PASSAGE. THE COURSE SHOULD HAVE BEEN STRAIGHT OUT. THE CAPT DID NOT HAVE COURSE INFO OFF TO R UNTIL VOR STATION PASSAGE. THIS SHOULD HAVE BEEN INCORPORATED IN DEP BRIEF WHEN AN IMMEDIATE STATION PASSAGE WILL OCCUR AS A REMINDER TO STAY THE COURSE.