INSTRUCTOR WITH SPI HAS RAMP CHK AND ACFT FOUND UNAIRWORTHY.

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I WAS TRAINING A PRIVATE PLT APPLICANT AT NUT TREE ARPT AT VACAVILLE WHEN AFTER 6 OR 7 TOUCH-AND-GOES AND/OR FULL STOP LNDGS I NOTICED A MUFFLED POPPING. I DEDUCED THE SOUND WAS COMING FROM AN EXHAUST PROB. AS I TAXIED TO THE RAMP IN ORDER TO INSPECT THE PROB; I WAS APCHED BY 2 SO- CALLED SAFETY OFFICIALS OF THE ARPT. THEY INFORMED ME THAT MY AIRPLANE HAD A NOISE PROB AND THAT IT SOUNDED LIKE IT WAS MISSING. THEY ADVISED ME TO TKOF AND TAKE IT BACK TO CONCORD; MY HOME BASE. I TOLD THEM THE AIRPLANE WAS NOT MISSING; AND THAT IT WAS DEVELOPING FULL PWR AND THE OIL TEMP AND PRESSURE WERE FINE. I ALSO SAID I WAS GOING TO USE THE MEN'S ROOM. I WENT INTO THE MEN'S ROOM WITH THE INTENT TO THOROUGHLY PREFLT THE AIRPLANE BUT UPON EXITING THE MEN'S ROOM; ONE OF THE 'SAFETY OFFICIALS' TOLD ME TO COME OUTSIDE; HE HAD SOMEONE ELSE I COULD TALK TO. I WENT TO THE AIRPLANE AND WAS TOLD BY MR. X THAT I WAS BEING RAMP CHKED. HE ASKED TO SEE MY CREDENTIALS AND I TOLD HIM I WOULD SHOW HIM; BUT NOT SURRENDER THEM. HE GOT MAD AND SAID I WAS REQUIRED BY LAW TO SHOW HIM THE CREDENTIALS. HE TOLD ME TO PLACE THE CREDENTIALS ON THE HORIZ STABILIZER AND HE COPIED SOME INFO. HE INSPECTED THE AIRPLANE AND FOUND IT TO BE UNAIRWORTHY. I AND MY STUDENT GOT A RIDE WITH ANOTHER CLUB MEMBER. I GOT A CALL FROM MR. Y; AN FAA OPS INSPECTOR; THE NEXT MORNING; DEMANDING TO SEE MY CREDENTIALS (INSTRUCTOR; PLT'S AND MEDICAL CERTIFICATE). I CALLED HIM BACK AND HE SAID HE MAY OR MAY NOT FILE FOR A VIOLATION AND THAT I WOULD HAVE TO MEET WITH HIM. I SAID OK AND AGREED TO MEET HIM AT HIS CONVENIENCE. HIS CONCERN; HE SAID; WAS WHETHER I WAS FLYING; KNOWINGLY; AN UNAIRWORTHY AIRPLANE AND IF I WAS GOING TO CONTINUE FLYING IT TO CONCORD. MY POS IS THAT I WAS NOT KNOWINGLY FLYING AN UNAIRWORTHY AIRPLANE AND I HAD NO INTENTION OF FLYING IT BACK TO CONCORD. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR STATES THE 2 'OFFICIALS' WHO FIRST APCHED WERE NOT FAA PERSONNEL. THEY HAD NO POS WHICH ALLOWED THEM TO REQUEST HIS CREDENTIALS. HE WAS WITH A STUDENT AND THEY WERE VERY OFFICIOUS. AN FAA MAINT INSPECTOR WAS AT THE ARPT FOR A MEETING AND THESE 2 BROUGHT HIM TO THE ACFT. ON INSPECTION IT WAS OBVIOUS THERE WAS A MUFFLER SEPARATION OF THE PIPE AND FLANGE; CAUSING A BACKFIRE EFFECT. THAT IS WHAT SOUNDED SO LOUD FROM THE GND. NOT AS LOUD IN THE ACFT. RPTR AGREED THE ACFT WAS UNAIRWORTHY AT THAT TIME AND DID NOT FLY IT. SINCE AGREEING TO MEET WITH THE OPS INSPECTOR HE HAS HAD NO FURTHER WORD FROM FAA.