A C550 PLT RPTS THAT HE HAD AN ACFT EQUIP PROB HIS GPS NAV SYS DROPPED OFF THE LINE MOMENTARILY. WHEN IT CAME BACK UP; IT HAD DROPPED A WAYPOINT. THE RPTR WENT TO THE NEXT WAYPOINT AND ARTCC NOTICED THE NAV ERROR.

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DURING CRUISE FLT AT FL220; THE KLN 90B GPS DROPPED OFF LINE FOR A MOMENT. WHEN IT CAME BACK ON LINE IT SHOWED US DIRECT PMD VOR WITH A FULL R SCALE DEFLECTION. I MISTAKENLY THOUGHT THAT WE HAD ALREADY PASSED DAG VOR DURING THE TIME THE GPS WAS 'OFF LINE' AND CTRED THE CDI AND PROCEEDED DIRECT PMD WHICH WAS PART OF OUR RTE CLRNC. ATC ASKED IF WE WERE PROCEEDING DIRECT DAG. WE SITUATED OURSELVES AND REPROGRAMMED THE GPS AND PROCEEDED TO DAG AND THEN DIRECT PMD. DUE TO LIMITED EXPERIENCE WITH THE KLN 90B AND GPS IN GENERAL; WE FAILED TO RECOGNIZE A LACK OF SITUATIONAL AWARENESS. IF WE HAD NOT BEEN PREOCCUPIED WITH THE GPS DROPPING 'OFF LINE' AND HAD BACKED OURSELVES UP WITH THE NAV RECEIVERS; THE ERROR COULD HAVE BEEN IMMEDIATELY RECOGNIZED AND CORRECTED. IN THIS DAY OF AUTOMATION AND GPS; ONE MUST NEVER FORGET TO ALWAYS BACK THEMSELVES UP WITH RAW DATA. (WE ALSO HAVE A PEDESTAL MOUNTED KNS-660 FMS.) WE HAVE DECIDED THAT ALTHOUGH WE HAVE A VERY AUTOMATED AIRPLANE; THE PF WILL TRACK THE ACFT'S POS WITH THE EFIS AND A RELIABLE CHART! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS NEW TO THE WORLD OF GPS. HE HAS FALLEN IN LOVE WITH IT; BUT HE DOES NOT YET TRUST IT COMPLETELY. HE ATTEMPTS TO BACK IT UP ALWAYS WITH VOR OR THE FMS. HE HAS SEEN HIS GPS DROP OFF THE LINE IN ISOLATED INSTANCES FOR NO MORE THAN 1 OR 2 MINS. HE HAS HEARD NOTHING FROM THE FAA ON THIS MATTER. HE DOES NOT BELIEVE THAT HE ENTERED THE RESTR AREAS NEAR DAG AND PMD.