PLT OF A PIPER CHEROKEE ARCHER; PA28-181; EXPERIENCED ERRATIC INDICATIONS FROM HIS HAND-HELD GPS NAV EQUIP. IT HAD BEEN PROVIDING ACCURATE INFO FOR 6 MONTHS AND THEN STARTED SHOWING ERROR MESSAGES INDICATING POOR RECEPTION COVERAGE.

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EVERY DAY THIS WK I HAVE HAD PROBS WITH GPS SVC BTWN SAN ANTONIO; MCALLEN; AND LAREDO; TX. I AM A PART 135 AIR FREIGHT PLT AND HAVE USED A GARMIN GPS 90 AS A SUPPLEMENTAL NAVAID FOR OVER A YR. THE GPS USUALLY WORKS VERY WELL. THIS WK AND 1 OR 2 DAYS LAST WK; THE GPS HAS BEEN UNSERVICEABLE MORE THAN IT WORKS. I GET ERROR MESSAGES SAYING 'POOR GPS COVERAGE' OR 'NEED 2- DIMENSIONAL ALT INFO.' IF THE GOV IS EXPERIMENTING WITH GPS COVERAGE IN SOUTH TEXAS; THEY ARE CAUSING A REAL PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAS SUBSEQUENTLY SENT THE GPS TO THE MANUFACTURER FOR REPAIR AND THAT THE PROBS HE EXPERIENCED WERE NOT CAUSED BY SOME TYPE OF GOV EXPERIMENTATION. HE STATED THAT IT WAS A NON IFR APPROVED GARMIN MODEL 90; AND THAT THE ACFT WAS EQUIPPED WITH 2 VOR RECEIVERS. HE FURTHER STATED THAT HE WAS FLYING BTWN 6500 FT AND 7500 FT SW OF THE THREE RIVERS VORTAC UNDER THE KINGSVILLE MOA AND ON TOP OF A 3000 FT OVCST WITH APPROX 10 MI VISIBILITY.