GA SMT WAS FLOWN WITHOUT PROPER MAINT WRITE OFF OF A LOGBOOK ITEM.

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WHILE RETURNING FROM A FLT ON NOV/WED/91; THE LORAN HAD FAILED AND INDICATED 'POSSIBLE LATITUDE/LONGITUDE GLITCH.' I WROTE IT UP ON A STANDARD RPT WHICH IS KEPT IN A PRIVATE AREA OF OUR OFFICE. OUR FIXED BASE OP HAS BEEN SUBJECT TO VARIOUS INSPECTIONS BECAUSE OF OUR 135 OPS (NOTHING FOUND IN ERROR). JUST MINOR PAPERWORK WHICH WAS CORRECTED. PART OF OUR SCOPE OF OPS IS THE MAINT/CREWING AND FUELING OF CUSTOMER'S ACFT WHICH RESULT IN FAR PART 91 OPS. ON NOV/FRI/91; I DEPARTED ON ANOTHER PART 91 FLT FOR THE OWNER. DURING PREFLT I DETERMINED THE LORAN UNIT WAS FUNCTIONAL (NOTE LORAN IS PLACARDED 'FOR VFR ONLY'). THE UNIT CONTINUED TO FUNCTION PROPERLY THROUGHOUT THE FLT TO AND FROM DEST. ON NOV/THU/91; AN FAA FSDO AVIONICS INSPECTOR WAS ON SITE IN ACCORDANCE WITH OUR BASE INSPECTION PROGRAM. THIS INDIVIDUAL WAS SHOWN OUR 'SQUAWK SHEET' AND DEMANDED A COPY OF SAME. WHEN OUR CHIEF PLT REFUSED; THE INSPECTOR THEN THREATENED THE CHIEF PLT WITH A VIOLATION; STATING THAT FOR A PART 91 ACFT IT WAS NECESSARY TO HAVE EACH MALFUNCTION SIGNED OFF AND DATED BY MAINT PRIOR TO FLT; AND THAT AS PIC; I WAS IN VIOLATION AND WOULD BE RECEIVING A 'LETTER OF INVESTIGATION.' THIS ACFT DOES NOT HAVE A MEL. THE ACFT IS OWNED BY A BANK WHICH SPARES NO EXPENSE FOR MAINT AND THE ACFT IS NOT FLOWN WITH DEFERRED ITEMS AND IS KEPT IN IMMACULATE CONDITION. THIS AGGRESSIVE BEHAVIOR BY FAA PERSONNEL BRING SEVERAL QUESTIONS TO MIND. WHERE DOES THE FAA HAVE THE RIGHT FOR ILLEGAL SEARCH AND SEIZURE (PART 91 SQUAWKS). WHERE UNDER PART 91 DOES IT SAY THAT MAINT ITEMS HAVE TO BE SIGNED OFF? (PART 135 YES) BUT MY UNDERSTANDING IS THAT PART 91 MAINT ITEMS CAN EVEN BE VERBALLY COMMUNICATED. WHAT ARE THE RULES REGARDING INTERMITTENT FAILURES AND THE REALITIES OF ECONOMICS WHEN TRYING TO FIND THESE PROBLEMS AND HOW IS ONE TO REGULATE THAT.