ACR WDB TRACK HDG DEV BECAUSE THE FLT CREW ENTERED THE WRONG LAT IN THE INS.

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A RECLRNC HAD BEEN ISSUED BY ZAN TO PROCEED FROM ST PAUL I (SPY); G469; ORDON; R580; OATIS; DIRECT KETAR; OTR-10; CVC. CAPT LOOKED UP COORDINATES FOR WAYPOINTS ALONG G469; AND R580; AND WROTE THEM ONTO ORIGINAL FLT PLAN FORM. AFTER HE INSERTED THESE COORDINATES INTO THE INS; I CHKED ALL WAYPOINTS AGAINST FLT PLAN. HOWEVER; HE WROTE DOWN AND INSERTED THE WRONG LATITUDE OF N.5302.5 FOR ONADE INSTEAD OF THE CORRECT LATITUDE OF N.5342.5. WHILE IN RADAR CONTACT AND APPROX 50 MI E OF ONADE. ANC ATC ADVISED US WE WERE S OF COURSE. ALL COORDINATES WERE CHKED AGAIN AND IT WAS DISCOVERED THAT THE INCORRECT N LATITUDE HAD BEEN INSERTED AFTER CHKING IT AGAINST COMMERCIAL CHART. LATITUDE WAS UPDATED; ACFT TURNED R TO GO DIRECT TO ONADE; AND CROSSED ONADE ON 328 DEG RADIAL 65 DME; APPROX 3 MI S OF COURSE. ALL FURTHER COORDINATES WERE DOUBLECHKED WITH BOTH NAV CHART AND COMMERCIAL CHART. A CONTRIBUTING FACTOR WAS THAT ONLY 2 INS UNITS WERE IN USE AS THE #3 IS WAS INOP AT DEP. THIS MADE IT MORE DIFFICULT FOR 3 PLTS TO CHK COORDINATES AND FOR BACK UP. ALSO NO BLANK FLT PLAN FORMS WERE AVAILABLE THUS MAKING IT MORE DIFFICULT TO READ RERTE ON EXISTING FLT PLAN. SUGGEST BLANK FLT PLAN FORMS BE STOCKED ON ACFT; MORE DILIGENCE ON PART OF ALL 3 CREW MEMBERS; AND CHK ALL COORDINATES WITH CHART PARTICULARLY WHEN RERTE IS INVOLVED.