FLC OF A LEAR JET 35 OVERSHOT ASSIGNED ALT DUE TO HAVING THE WRONG ALTIMETER SETTING CAUSED BY NO RADIO CONTACT ON THE GND AT A NON TWR ARPT.

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WE ARE A PART 91 OP OF THE LEAR 35 INVOLVED. THE OWNERS WANTED TO GO INTO A NEW EAGLE PASS; TX; ARPT (5T9); WHICH IS VFR ONLY WITH NO SVCS (JET FUEL) PROVIDED. I BELIEVE THIS IS THE FIRST TIME IN THE YR I'VE BEEN WITH THE COMPANY THAT WE HAVE GONE INTO A VFR ONLY ARPT WITH THE LEAR. THE COMPANY PROVIDES NO VFR CHARTS FOR THE AIRPLANE. ON THIS PARTICULAR DAY THE COMPANY HIRED A QUALIFIED PLT TO BE THE SIC; BUT HE USUALLY FLIES A DIFFERENT MODEL LEARJET SO HE WAS A LITTLE AWKWARD WITH WHERE THINGS ARE PLACED AND PROCS. THE ARPT REALLY HAS NO ARPT ADVISORIES; AS THE UNICOM FREQ IS RARELY ANSWERED. WHILE TAXIING OUT FOR TKOF; WE TRIED TO PICK UP OUR IFR CLRNC ON THE FSS RECOMMENDED FREQ; BUT WAS UNABLE TO REACH ANYONE. WE NEXT TRIED THE PHONE NUMBER THE FSS BRIEFER SAID TO TRY; WHICH WAS ALSO UNSUCCESSFUL. WE THEN VERIFIED THE AIRSPACE AROUND US ON A LOW ENRTE (IFR) AND TOOK OFF VFR TO PICK UP OUR CLRNC AIRBORNE. HERE IS WHERE THE PROB OCCURRED. A CREW THAT DOESN'T USUALLY WORK TOGETHER; TOOK OFF USING PROCS NOT NORMALLY USED BY THEM; AFTER NUMEROUS ATTEMPTS WERE MADE TO CONTACT ATC FOR A CLRNC. WITH NO AWOS/ASOS AVAILABLE; AN UNMONITORED UNICOM; AND NO ATC CONTACT; THE CURRENT ALTIMETER SETTING WAS NEVER SET. WE STILL HAD SET 29.99 FROM THE DAY BEFORE. AS WE BECAME AIRBORNE; WE PICKED UP OUR CLRNC FROM DEL RIO DEP AND THEY TOLD US TO LEVEL 6000 FT. AFTER BEING LEVEL AT 6000 FT FOR A FEW MINS; THEY RESPONDED THAT THE CURRENT ALTIMETER IS 30.42 WHAT IS YOUR ALT; WHICH WE THEN SHOWED 6400 FT AND DSNDED TO 6000 FT. OBVIOUSLY; WHEN IT COMES DOWN TO IT; IT WAS PLT ERROR. WITH A LITTLE SEARCHING; WE COULD HAVE FOUND OUT FIELD ELEVATION AND SET THE ALTIMETER. THIS WAS OVERLOOKED BY THE CREW WHEN ALL THE ATTEMPTS TO CONTACT ATC FAILED AND THE HURRIED; NOT NORMAL CREW DEPARTED VFR USING IFR CHARTS.