PLT OF VINTAGE CZECH JET TRAINER SUFFERS GPS FAILURE AND ENTERS CLASS A WITHOUT A CLRNC OR FLT PLAN. LATER FLIES THROUGH MIL CLASS D WITHOUT RADIO CONTACT ACCOUNT FUEL CONCERNS.

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I WAS RETURNING FROM ZZZ1 TO ZZZ2 WHEN MY C1000 GPS STARTED BLINKING AND SHOWING UNRELIABLE NAV INFO. OPTING TO DIAL IN MY VOR FROM ZZZ3 VOR 245 DEG RADIAL DIRECT ZZZ4; I WAS SKEPTICAL OF THE SIGNAL FROM ZZZ3 EVEN THOUGH IT WAS SHOWING MOVEMENT; I DIALED IN TO ZZZ1. AGAIN THE NEEDLE SHOWED MOVEMENT. AS THESE VORS ARE IN VALLEYS WITH TERRAIN RISING TO 11000 FT AND SURROUNDING; I THOUGHT IT MIGHT BE PRUDENT TO CLB AND SEE IF A STRONGER SIGNAL WAS AVAILABLE. AT +/-FL204 IT WAS NOT SHOWING ANY RELIABLE SIGNAL. IN THE PROCESS OF FOLLOWING UNRELIABLE SIGNALS I DECIDED TO LAND AT ZZZ5 TO REFUEL AND DEVELOP A BETTER STRATEGY. PRIOR TO LNDG AT ZZZ5; I ISSUED AN EMER ON 121.5 HOPING TO GET RECEPTION FROM ZZZ6 AND A RADAR STEER TO ZZZ2. I DID NOT RECEIVE ANY RESPONSE FROM ANYONE; HOWEVER; MY DECLARATION OF AN EMER WAS RECEIVED BY SOMEONE (?). AS THE MIL STARTED CALLING PERTINENT PEOPLE; ONE OF WHICH WAS MY LCL FBO OPERATOR; HE DIALED MY CELL NUMBER AND ASKED ME 'WHERE IN THE &*%$ ARE YOU?' AFTER THAT ISSUE WAS RESOLVED; I BORROWED A SMALL GPS FROM A YOUNG MAN AT ZZZ5 AND TOOK OFF FOR ZZZ2. THE SHORTEST DISTANCE WAS OVER RESTR AIRSPACE. I OVERFLEW THAT AREA; AND I BROADCAST IN THE BLIND AGAIN THAT I WAS OVERFLYING THEIR AIRSPACE. SUBSEQUENTLY; UPON LNDG AT ZZZ2; I CALLED BY TELEPHONE TO THE PIO AND LEFT A RECORDED MESSAGE REGARDING MY OVERFLT AND THE ISSUE OF FUEL FOR THE REASON OF DIRECT FLT TO ZZZ2.