A FALCON 2000 CREW MISSED THE FMC NOT PROPERLY INITIALIZING DURING PREFLT. THE CREW WAS UNABLE TO COMPLETE AN AUTOMATED DIRECT TO A NAVAID COMMAND.

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AT GEAR RETRACTION; THE GPWS WENT ACTIVE. ALTHOUGH WE KNEW OUR POS; STILL OVER THE RWY; WE COMPLIED BY EXPEDITING OUR CLB. OUR INITIAL CLRNC WAS RWY HDG; RADAR VECTORS. WHILE THE GPWS WAS BLARING; WE WERE GIVEN SEVERAL HDG AND ALT CHANGES. WE KNEW WE WERE ABOVE MSA AND WE COMPLIED. AS A CREW; WE SUSPECTED A PROB WITH EITHER THE RADAR ALTIMETER OR THE GPWS SYS. THIS SUSPICION WAS INCORRECT; BUT SINCE THE VECTORS PUT US IN A GOOD POS; WE STARTED THE SOMEWHAT COMPLEX OPERATIONAL CHK FLT PROFILE. DURING THIS TIME WE WERE ISSUED ALTERNATELY HDGS AND CLRNCS TOWARD FFO VOR. BECAUSE THESE CHANGES KEPT OCCURRING; IT WAS NOT INITIALLY OBVIOUS THAT THE FMS HAD OUR CURRENT POS WRONG. EACH 'DIRECT' WAS ACCOMPANIED WITH A GREEN NEEDLE ON PFD #1 AND THE NORMAL FMS AND NAV INPUTS. 2 OTHER FACTORS -- THE VERY HIGH WORKLOAD AND THE INABILITY TO BACK UP FFO USING OTHER VOR OR ANY BEARING POINTER; BECAUSE IT WAS OTS AND NOT NOTAMED -- CONTRIBUTED TO US NOT IMMEDIATELY DETECTING THE TOTALITY OF OUR PROBS. FURTHER; BECAUSE OF PRIMARILY BEING ON HDGS WHICH ATC KEPT CHANGING; WE WERE VERY BUSY COMPLYING WITH AND COMPLETING THE OPERATIONAL CHK FLT; WE DIDN'T FULLY REGISTER THE SIGNIFICANCE OF OUR CHK POS MESSAGE. EVENTUALLY; WE REALIZED THAT OUR VORS WERE STILL WORKING. WE HAD DONE A VOR CHK ON THE GND; AND FFO'S WAS NOT AND OUR FMS POS AND DISPLAY WAS WAY OFF. AGAIN; THIS WAS MARKED BY BEING PRIMARILY ON HDGS; THE PREVIOUS GPWS WARNING AND THE EXTREMELY HIGH WORKLOAD; WHICH WE WERE CONTRIBUTING TO. WE ALSO PULLED UP OUR NAV STATUS PAGE AND FOUND THAT NOT ONLY WERE WE SINGLE SOURCE NAV; THE ONE SOURCE A LONE IRS WAS WAY OFF. THE RESULT WAS OUR ATTEMPTS TO GO DIRECT TO FFO WERE PROBLEMATIC AS WERE OUR ATTEMPTS TO DO SO BY ALTERNATE MEANS. ONCE THIS BECAME OBVIOUS; WE WERE ABLE TO MANUALLY CALL UP OTHER VORS; ETC; AND EVENTUALLY REINITIALIZE OUR POS AND THEN BACK UP EVERY INPUT -- EXCEPT FFO -- MANUALLY. HOW THE IRS WAS SO FAR OFF; WHY WE WERE IN SINGLE SOURCE NAV; AND WHY NONE OF THE OTHER BLENDED INFO WAS BEING PROCESSED I DO NOT KNOW. THERE WERE A LOT OF FACTORS THAT COLLECTIVELY CONTRIBUTED TO THIS SIT AND FORTUNATELY THE ERROR CHAIN WAS BROKEN. THERE ARE SOME THINGS THAT COULD BE DONE TO REDUCE THIS TYPE OF EVENT FROM OCCURRING IN THE FUTURE. AMONG THEM ARE THAT THIS TYPE OF OCF BE CONDUCTED ONLY IN VMC. THAT SUCH COMPLEX PROFILES NOT BE CONDUCTED IN SUCH CLOSE PROX TO HIGH DENSITY CLASS B AIRSPACE. THAT BOTH PLTS 'SHOW' AT THE AIRPLANE AT THE SAME TIME AND ARE BOTH ON THE FLT DECK DURING THE AVIONICS SET-UP WHEN A PLANE IS COMING OUT OF MAINT. THAT BEFORE STARTING ON AN OCF SEGMENT NORMAL FLT PERFORMANCE INCLUDING NORMAL NAV ARE VERIFIED INFLT.