As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FLIGHT CREW DESCRIBED THAT WHEN THEY ENTERED THE FLIGHT PLAN INTO THE FMS THERE WAS NO ISSUE. BUT WHEN THEY SHUTDOWN THE AVIONICS BEFORE STARTING THE ENGINES AND WHEN AVIONICS WERE ACTIVATED AGAIN THE FMS POSITION WAS LOST. THE BASE MAINTENANCE TEAM REMOVED AND REPLACED THE FMS GPS ANTENNA WITH A NEW ASSEMBLY. OPERATIONAL CHECKS WERE SATISFACTORY. THE AIRCRAFT WAS THEN RETURNED TO SERVICE.