HDG TRACK POS DEV IN GROSS NAV ERROR.

Narrative

IN SUM: CPR CHIEF PLT AND FO INDEPENDENTLY FIGURED LATITUDE/LONGITUDE COORDINATES FOR DEP ARPT; EWR; NJ. DID NOT USE ARPT IDENT AND ASSOCIATED ARPT COORDINATES AS NORMALLY DONE FOR DOMESTIC FLTS. RECEIVED EQUIP WARNINGS AFTER THE FIRST UPDATE ON POS OVER FIRST FIX AFTER COMMAND BARS COMMAND DISAGREED WITH VOR NAV POS. INITIAL IRS DIFFERENTIAL WARNING MESSAGES WERE 3; 6; ETC. OTHER UPDATES PERFORMED AT CYQX DONE AND CREW WERE SATISFIED WITH PLOT ON TRACKS DURING THE FLT ABOVE THE MNPS AIRSPACE AT FL410. IN RADAR CONTACT WITH SHANNON CTL THEY WERE ADVISED THAT THEY WERE 81 NM N OF COURSE. RPTR SAYS THIS WAS AN INITIALIZATION ERROR; SOMETIMES CALLED A 'FINGER' ERROR. RPTR STATED THAT HE WOULD USE THE ARPT COORDINATES FROM NOW ON AND INDEPENDENTLY HAVE THE FO AND HIMSELF CHK THEIR IRS POS ON THE RWY. FURTHER; THAT WITH ANY WARNING DISPLAY AT ALL; HE WILL LAND AT THE SUITABLE ARPT FOR CORRECTIONS. ERROR ADMITTED WHILE STATING THAT HE IS VERY FAMILIAR WITH EQUIP AND DIDN'T THINK THIS COULD HAPPEN TO HIM. SAYS THEY WERE NOT COMPLACENT BUT STILL SUBJECT TO HUMAN ERROR.