THE FLC DID NOT FOLLOW THE APPROPRIATE PROC FOR THE MEL ON THE FMC. THE FLC DEVIATED FORM ASSIGNED HDGS BECAUSE THEY WERE IN THE ATTITUDE MODE RATHER THAN THE NAV MODE.

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ACFT HAD FMS MEL'D INOP DUE TO NAV DATABASE WOULD NOT LOAD. SELECTED IRU CTLS TO ATTITUDE ONLY. THIS WAS THE PROPER PROC FOR THE ACFT I HAD FLOWN UP TO NOW; UNFORTUNATELY NOT FOR THE MD88. INFLT; CTR QUESTIONED OUR HDG SEVERAL TIMES. AT THIS POINT I DID SOME DIGGING THROUGH BOOKS AND REALIZED IN ATTITUDE MODE; THE IRU MUST BE UPDATED EVERY 10 MINS THROUGH FMC CDU. IT WAS AT THIS POINT I LEARNED BOTH FMC CDU UNITS WERE FROZEN ON IDENT PAGE. BY PULLING AND RESETTING NUMEROUS CIRCUIT BREAKERS; EVENTUALLY REGAINED CTL OF FO CDU AND UPDATED HDG FROM MAGNETIC COMPASS. WE HAVE CHKLISTS FOR EVERYTHING TO DO WITH FMS; EXCEPT DISPATCH WITH FMS INOP. I SHOULD HAVE SELECTED IRU TO NAV AND INITIALIZED POS THROUGH FMS CDU. CONTRIBUTING TO PROB WAS SEVERAL DISTRACTIONS DURING PREFLT; INCLUDING THE FACT COPLT WAS LATE (DUE TO THE FACT THE DRIVER FROM HOTEL HE WAS COMING FROM GOT LOST ON ARPT PROPERTY); AND I COULDN'T GET CREW SCHEDULE OR FLT CTL ON THE PHONE (BUSY SIGNALS). NOT REALLY AN EXCUSE THOUGH FOR NOT MORE THOROUGHLY RESEARCHING THE SIT I HAD.