INTL FLC MISUNDERSTOOD DEP CLRNC.

Narrative

A FLT PLAN CSS-UIO WAS PROVIDED BY DISPATCH DEPARTING MIA. ROUTING DEPARTING CCS WAS: MARES 1 DEP NOL ALBAN ACR X; ETC. UPON ARR IN CCS; THIS INFO WAS ENTERED INTO THE FMS. DURING GND OPS; THERE WAS MENTION OF ANOTHER FLT PLAN FOR THE SAME RTE SEGMENT; BUT I NEVER SAW THIS PLAN. STANDARD PRACTICE IN SOUTH AND CENTRAL AMERICA IS TO GET THE CLRNC WHEN TAXIING OR PUSHED BACK; AS WAS THIS CASE. THE CLRNC WAS; 'V10 VIA ACR X; MARES 1 DEP; SQUAWK XXXX.' 'ROGER' THE READBACK. AFTER DEP; WE FLEW THE MARES 1; WHICH IS OUTBOUND ON THE 319 DEG RADIAL MIQ; 17 MI FOR MARES. JUST PRIOR TO REACHING MARES; THE CAPT STARTED A TURN FOR NOL WHICH WAS ON OUR ORIGINAL FLT PLAN. (THE MARES 1 DEP INFO ENDS AT MARES.) (I (FO) ALSO AM NOT PROVIDED WITH CHARTS TO REVIEW.) ATC IMMEDIATELY ADVISED WE ARE ESSENTIALLY OFF COURSE; AND WERE SUPPOSED TO FLY TO ATONO FURTHER UP THE R319 MIQ; 37 MI; THENCE PBL. WE IMMEDIATELY TURNED BACK AND CONTINUED AS ATC ADVISED. ERROR OFF COURSE WAS APPROX 5-6 MI; OUR TURN WAS 90 DEGS FROM COURSE. THE ERROR CHAIN WHICH LED TO THIS EVENT BEGAN WITH DISPATCH PROVIDING US WITH AN ERRONEOUS FLT PLAN; WHICH WAS ENTERED INTO THE FMS. THE NEXT ERROR WAS NOT COMPARING THE 2 FLT PLANS WE WERE LATER GIVEN. FURTHERMORE; A HANDWRITTEN ICAO PLAN WAS PROVIDED TO THE CAPT; SIGNED FOR; AND NEVER COMPARED WITH COMPANY PLAN. FINALLY; THE DEP AND RTE WAS ONLY BRIEFED TO THE MINIMUM INFO. ONCE WE DEPARTED AND IN OUR TURN OVER MARES; I KNEW SOMETHING WAS WRONG AND ADVISED THE CAPT TO TURN BACK; BEFORE ATC CALLED. I SHOULD HAVE BEEN MORE ATTENTIVE AND AGGRESSIVE IN PREVENTING THIS SIT.