A320 ACFT DURING CLB THE MCDU INDICATED 'CHK ACFT POS.' FLC CHKED NAV COMPUTERS AND NOTED THAT ALL 3 IRS DEVS WERE 99 PT 9 MI IN ERROR. FLC ADVISED ATC THAT THEY WERE NO LONGER IRS NAV EQUIPPED. AFTER LNDG AND PARKED AT GATE; THE FMCS WERE VERY ACCURATE BUT IRS' WERE STILL IN ERROR.

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ON OCT/XX/96; WE WERE ASSIGNED TO FLY FROM ANC TO SFO. AS AN A320 LINE CHK AIRMAN; I OCCUPIED THE R SEAT DURING THIS FLT AND PERFORMED PNF DUTIES; WHILE CONDUCTING IOE WITH CAPT WHO OCCUPIED THE L SEAT AND PERFORMED PF DUTIES DURING THIS FLT. WE ARRIVED AT THE ACFT AT 30 MINS PRIOR TO SCHEDULED DEP. THE TEMP AT THE TIME OF DEP WAS APPROX 17 DEG F. THE ACFT HAD REMAINED OVERNIGHT FOR 13 HRS AND THIS WOULD BE THE FIRST FLT OF THE DAY. UPON ENTERING THE COCKPIT; I TURNED ALL 3 OF THE IRS UNITS FROM THE OFF POS TO NAV AND THEN CONDUCTED A PREFLT EXTERIOR INSPECTION WHILE IOE CAPT A CONDUCTED THE COCKPIT SETUP. THE IRS ALIGNMENT WAS COMPLETED BY CAPT A INITIALIZING THE MCDU (MULTIFUNCTION CTL AND DISPLAY UNIT) PAGE A. THE PRESENT POS WAS INSERTED AS 'PANC' AND THE CORRECT LATITUDE AND LONGITUDE WAS VERIFIED AS THAT SHOWN ON THE COMMERCIAL CHART 10-9 PAGE. DURING THE PREFLT ALL 3 IRS'S ALIGNED NORMALLY AND THE MAP CORRECTLY INDICATED OUR POS ON THE ANCHORAGE ARPT AND IN RELATIONSHIP TO RWY 32 WHICH WAS THE SELECTED DEP RWY. THE TAXI OUT AND TKOF FROM RWY 32 WAS UNEVENTFUL. 2 MINS AFTER TKOF THE MCDU INDICATED 'CHK ACFT POS.' A CHK OF THE R MCDU POS MONITOR PAGE INDICATED THE FOLLOWING: FMC OWN: 6110.3N/14918.9W; FMC OPP: 6110.3N/14919.3W; RADIO 6110.3N/14919.0W; IRS MIX: 61103N/13404.7W; ALL 3 IRS DEVS INDICATED 99.9 NM. A CHK OF ALL 3 IRS UNITS PRESENT POS ON THE OVERHEAD ADIRS CTL DISPLAY UNIT INDICATED THAT ALL 3 UNITS WERE AT 6110.3N/13404.7W WHICH WOULD PUT OUR POS IN THE VICINITY OF THE YXY VOR; SOME 440 MI E OF OUR ACTUAL POS. WE ADVISED ATC WE WERE NOW A 'SLASH ALPHA' EQUIP SUFFIX AND WE PROCEEDED UNEVENTFULLY VIA HIGH ALT AIRWAYS TO SFO. WHILE ENRTE WE CONTACTED DISPATCH; AND MAINT COORDINATOR AND ATTEMPTED TO CONTACT THE A320 FLEET; TO ADVISE THEM OF THIS ANOMALY. MAINT COORDINATOR ADVISED THAT WE WOULD BE MET IN SFO BY AIRBUS REPRESENTATIVE AND LINE MAINT. AFTER PARKING WE LEFT THE IRS UNITS IN THE NAV POS SO THAT MAINT WOULD BE ABLE TO OBSERVE THE IRS AND FMC POS. WHILE PARKED AT GATE IN SFO; A CHK OF THE R MCDU POS MONITOR PAGE INDICATED THE FOLLOWING: FMC OWN: 3737.2N/12223.6W; FMC OPP: 3737.2N/12223.4W; RADIO (BLANK); IRS MIX: 3737.5N/10708.6W. ALL 3 IRS DEVS INDICATED 99.9 NM.