FLC OF ACR WDB ACFT INADVERTENTLY ALLOWED ACFT DURING HIGH ALT CRUISE TO TURN OFF INTENDED TRACK RESULTING IN A GROSS NAV ERROR.

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ON TRANSOCEANIC FRA TO DTW IN RADIO CONTACT WITH MONTREAL CTR AT FL350 WE LOST VHF RADIO CONTACT WITH MONCTON CTR AND WAS ATTEMPTING TO FIND A FREQ FOR MONTREAL CTR AT THE SAME TIME WE WERE APCHING YFM. THE INS WENT TO THE NEXT INS POINT THAT WAS NOT PROPERLY LOADED. THE ACFT STARTED INTO A TURN TO THE E AS I SAW THE ADF NEEDLE FOR YFM SWING. IN THE CONFUSION WITH THE RADIO; 3-4 MINS WENT BY WHEN I NOTICED THE HDG WAS APPROX 150 DEGS (90 DEGS OFF COURSE L). I STARTED AN IMMEDIATE TURN BACK TO 230 DEGS. WE ENTERED RADAR RADIO CONTACT WITH MONTREAL AND WERE ADVISED WE WERE 50 MI OFF COURSE. THE CONFUSION FACTOR LED TO THE INS DISCREPANCY RESULTING IN THE ACFT TURNING OFF COURSE. FROM A HUMAN FACTORS STANDPOINT I SUCCUMBED TO MISAPPROPRIATE PRIORITIES. CONCERN OVER THE LOST VHF COM PROBLEM ALLOWED ME TO CHANNEL MY ATTN ON ASSISTING THE CAPT TO FIND A NEW FREQ. THE FACT THAT THE ACFT WAS TURNING IN THE PROPER DIRECTION CAUSED ME TO NOT WATCH WHERE THE PLANE WAS TURNING. IN ADDITION; THE AUTOPLT WAS ON A 10 DEG BANK ANGLE; THEREFORE; THE SHALLOW BANK DIDN'T TRIGGER A CUE THAT WE WERE IN A LARGE DEG OF TURN.