AN EMB 145 EXPERIENCED DUAL GPS FAILURES CAUSING AN FMS LNAV DIFFERENCE BETWEEN THE CAPT AND FO. THE EICAS DID NOT ALERT ABOUT THE GPS FAILURES.

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I SET UP MY FMS WITH THE DEP PROC. ALL REQUIRED CHECKS OF THE FMS WERE COMPLETED ACCORDING TO FM1 AND AOM V1. BOTH FMS 1 AND 2 WERE SET CORRECTLY. DURING THE TAXI CHECKLIST BOTH FMS'S WERE CHECKED AND WERE SET CORRECTLY FOR RWY. AFTER A NORMAL TAKEOFF; NAV WAS SELECTED. I NOTICED THAT MY FMS DISPLAY SHOWED US RIGHT OF COURSE AND FO'S FMS DISPLAYED SHOWED US LEFT OF COURSE WITH NO MALFUNCTION INDICATION. THE FO WAS FOLLOWING THE FLIGHT DIRECTOR BARS UNTIL I NOTIFIED HIM OUR FMS INDICATIONS WERE NOT THE SAME. AT THAT TIME HE ROLLED THE WINGS LEVEL. SHORTLY AFTER ATC ASKED FOR OUR HEADING AND ASSIGNED US A NEW HEADING. WE STILL HAD NO MALFUNCTION INDICATIONS. WE WROTE IT UP ENROUTE AND FLIGHT CREW PLACARDED BOTH FMS'S. DISPATCH; MAINT CTL; AND ATC WERE NOTIFIED OF THE FAILURES. WE NOTIFIED ATC THAT WE WERE NEGATIVE RNAV AND THAT GPS'S HAD FAILED. WE CONDUCTED THE REMAINDER OF THE FLIGHT UNDER CONVENTIONAL NAVIGATION.SUPPLEMENTAL INFO FROM ACN 748407: ALL INDICATIONS SHOWED THE UNITS FUNCTIONING PROPERLY ON PREFLIGHT AND TAXI AND THERE WAS NO WARNING WHEN THE GPS'S FAILED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO STATED THAT A POWER INTERRUPTION AT THE GATE PRIOR TO PUSHBACK MAY HAVE INITIATED THIS EVENT ALTHOUGH HE SEES NO REASON WHY AN FMC OR EICAS ALERT MESSAGE WAS NOT GENERATED AS IT SHOULD HAVE BEEN. THE EMB145 FMC AUTOMATICALLY ADJUSTS RNP FOR THE PHASE OF FLIGHT AND TYPE OF DEPARTURE/ARRIVAL/APPROACH BEING FLOWN. THE RNP AND GPS STATUS IS AVAILABLE IN THE FMC BUT THE CORRECT PAGE MUST BE SELECTED TO VIEW IT.