DC10 MAKES GROSS NAV ERROR OVER ATLANTIC.

Narrative

WE INSERTED THE FLT PLAN INTO THE 3 INS'S IN LGW. WHEN WE OBTAINED OCEANIC CLRNC; THE FIRST 2 FIXES WERE CHANGED FROM THE ORIGINAL AND WE WERE CLRED TO THE FIRST NEW FIX IMMEDIATELY. THAT FIX WAS INSERTED AND THE ACFT PROCEEDED TO THE FIRST NEW FIX. WE THEN LOST CONTACT WITH SHANNON VHF. TRIED 4-6 (SEVERAL) FREQS OVER THE NEXT 8-10 MINS AND THEN BEGAN TRYING HF FREQS. FINALLY MADE CONTACT. CREW OVERLOAD; DUTIES; CAUSED US TO FAIL TO INSERT SECOND REVISED FIX DUE TO RADIO CONTACT ATTEMPTS. THE ACFT ATTEMPTED TO PROCEED TO ORIGINAL #2 FIX. WE CAUGHT THE ERROR ON THE 2 DEG CHK; BUT BY THAT TIME WE WERE APPROX 45 MI OFF COURSE IN UNLIMITED VISIBILITY CONDITIONS. VFR WAS MAINTAINED AT ALL TIMES. NO OTHER ACFT WAS OBSERVED EITHER AHEAD; ABOVE; OR BELOW US. WE MADE AN IMMEDIATE CORRECTION TO JOIN THE PROPER FLT PLAN AT FIX #3. NO FURTHER ACTION WAS REQUIRED. ANOTHER FACT TO SHOW THAT A SIGNIFICANT NUMBER OF NAV ERRORS OCCUR WITH REVISED FLT PLANS. WE WERE NO EXCEPTION. SHOULD HAVE RECHKED AND CHKED THE 2 REVISED FIXES AFTER RECEIVING THEM INSTEAD OF SPENDING MINS TRYING TO ESTABLISHED COMS.