LOSS OF NAV UNTIL WHILE IN AN MNPS AREA. LOSS OF ENG CAUSING ACFT TO DSND. THE MNPS (MINIMUM NAV PERFORMANCE SYS) REQUIRES 2 NAV UNITS WORKING AT ALL TIMES.

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OUR COMPANY ACFT; A LEAR 55LR IS CERTIFIED AND EQUIPPED FOR OPS IN MNPS AIRSPACE WITH DUAL LONG RANGE NAV SYS. ON FEB/AB/95; WE LEFT GREEN BAY; WI FOR A TRIP TO EUROPE WITH A STOP IN GANDER; NFLD ENRTE TO OUR FIRST STOP; MUNICH; GERMANY. ON THE OUTBOUND LEG FROM GANDER; AT APPROX 45 DEGS WEST; FL410; OUR ADVANCED NAV 7000 FMS LORAN C BECAME INOP. WE WERE OUT OF RADAR RANGE AT THIS TIME SO WE CONTINUED OUR FLT PER THE CONTINGENCY OF MNPS MANUAL. WE WERE ABOVE MNPSA AT FL410 AND WE DO HAVE A BACKUP STAND ALONE GPS NAV SYS FOR SUCH CONTINGENCIES. BEFORE FLT; WE HAD RECEIVED NOTAMS AND NONE INDICATED ANY PROBS WITH THE LORAN SYS. AFTER MANY FLTS IN EUROPE AND OUR LORAN STILL NOT WORKING; WE PLANNED OUR RETURN FLT VIA THE ICELAND SINGLE NAV MNPS RTE. ON LNDG AT KEFLAVIK WE DISCOVERED AN OIL LEAK IN THE #1 ENG AND GNDED THE ACFT. A MECH FROM THE US WAS DISPATCHED TO REPAIR AND RETURN THE ACFT TO SVC. ON FEB/AC/95; WE DEPARTED KEFLAVIK AT XA19(L) FOR GOOSE BAY; CANADA. APPROX 1 HR INTO THE FLT AT FL390; THE OIL PRESSURE ON THE #1 ENG BEGAN FLUCTUATING AND THE CABIN BEGAN TO FILL WITH OIL SMOKE. WE SHUT THE ENG DOWN AND FOLLOWED OCEANIC PROCS TO STEER OFF AIRWAYS; DECLARED AN EMER SINCE WE COULD NOT HOLD ALT ON 1 ENG AND ATC CLRED US BACK TO KEFLAVIK WHERE WE LANDED WITH NO FURTHER PROBS. I SUBSEQUENTLY DISCOVERED THAT ICELAND HAD RECENTLY SHUT DOWN IT'S LORAN C SYS. THIS EXPLAINED THE SYS NOT WORKING ON THE ACFT. I SUBSEQUENTLY DUG OUT MY MNPSA OPS MANUAL TO REVIEW IF WE HAD FOLLOWED PROPER PROCS WHICH AT THAT TIME I BELIEVED WE HAD. I DISCOVERED WE HAD FILED; RECEIVED A CLRNC FOR AND FLOWN THE RTE ADJACENT TO THE ONE PRESCRIBED FOR MNPS SINGLE NAV OPS. THIS IS THE RTE FILED BY OUR HANDLER IN HOUSTON. OUR NOTAMS RECEIVED FROM THE SAME HANDLER HAD NO MENTION OF THE DEGRADATION OF THE LORAN SYS. HOWEVER A DIRECT PHONE CALL TO THE UNITED STATES COAST GUARD WOULD HAVE CONFIRMED THAT FACT. I ALWAYS REVIEW MY MNPS MANUAL BEFORE LEAVING FOR EUROPE; HOWEVER THIS TIME I WAS SO BUSY WITH MANY PROJECTS THAT I PLAIN FORGOT TO DO THIS. THIS SIMPLE ACT WOULD PROBABLY HAVE PREVENTED OUR INADVERTENTLY FLYING A NON-APPROVED RTE. STRESS AND FORGETFULNESS CAUSED ME TO MISS BOTH THESE ITEMS. IN FUTURE OCEANIC OPS; I PLAN TO USE A DEDICATED CHKLIST TO ASSURE ALL BASES ARE COVERED BEFORE GETTING OFF THE GND TO ASSURE THERE IS NO RECURRENCE OF THESE OMISSIONS.