CORP MDT TRACK DEVIATION NORTH ATLANTIC.

Narrative

WERE REPORTED 17.8 MILES NORTH OFF COURSE AT 49/50 ENROUTE FROM SHANNON TO GANDER. BY GANDER CONTROL WAS USING 2 FMS EACH WITH 2 VLF OMEGA; 2 IRS; 2 VPU FOLLOWED ALL PROCEDURES ESTABLISHED BY COMPANY. FIRST BOTH IRS' DRIFTED OFF COURSE BY 17 MILES THEN CAME BACK. VLF'S WERE DRIFTING AS WELL TO AS MUCH AS 22 MILES. ALL OF THEM TOGETHER NOT BEING ABLE TO DESELECT PER COMPANY PROCEDURES WE CONTINUED ON OUR BLENDED POSITION AS DESCRIBED IN COMPANY FMS FLIGHT MANUAL. AT GANDER AIRPORT BOTH FMS WERE OFF BY 12 MILES AFTER USING THE VPU'S FOR 150 MILES. THIS PROBLEM WAS ESCALATED TO THE TOP LEVEL OF MGMNT OF MFG AND COMPANY. PRESENTLY AWAITING ANSWERS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE IRS UNITS WERE IN FACT CORRECT AND THE VLF/OMEGA SETS WERE IN FACT DRIFTING AND SINCE COMPANY PROC IS TO FLY THE VLF SINCE IT CAN DIRECT THE A/P BY LOCK ON AND THE INERTIAL CANNOT. SINCE THIS INCIDENT THE ACFT MFR HAS FLOWN THEIR TEST ACFT ON THE ROUTE AND FOUND THEIR OMEGA HAD THE SAME DRIFT PROBLEM. NOW BELIEVE IT IS AN INSTALLATION PROBLEM AND THE OMEGAS ARE BEING AFFECTED BY THE ACFT EQUIPMENT. IN THIS ACFT THEY DID FIND OCCILATORS IN OMEGAS WERE OVERHEATING AND CAUSING DRIFT SO MANUFACTURER IS LOOKING FOR SOLUTION; POSSIBLY RELOCATING THE OMEGA UNITS WHICH ARE NOW LOCATED UNDER THE MIDDLE ENGINE AND BEING AFFECTED BY ENGINE RF NOISE. IN INTERIM COMPANY HAS CHANGED PROC AND USING THE TWO INERTIAL SETS FOR PRIMARY LONG RANGE OVERWATER NAV AND OMEGA FOR BACKUP.