ATX PLT OPERATES SMT OUTSIDE OF MEL; MEL REQUIREMENTS; IN OP OF PAX FLT. FARS HAZY.

Narrative

I AM PIC ON A SINGLE PLT PART 135 CERTIFICATE. OUR ATX IS OPERATED WITH AN MEL APPROVED IN OUR OPS SPECS. 12-13 DAYS PRIOR TO THIS FLT; THE ELECTRIC TRIM FAILED. MAINT WAS DEFERRED PER THE MEL. 10 DAYS IS THE MAX PERIOD ALLOWED FOR CORRECTION UNDER THE MEL. ON THE DATE OF THIS FLT; I ANTICIPATED REPAIR OF THE TRIM BEING COMPLETED. WHEN MY FLT WAS DUE TO DEPART (FOR PART 91 SIGHTSEEING) I WAS INFORMED THAT THE REPAIR WAS NOT COMPLETE. I ATTEMPTED TO DETERMINE WHETHER THE FLT COULD DEPART LEGALLY UNDER PART 91; UNDER THE PROVISIONS OF FAR 91.213 (INOPERATIVE EQUIP). THE PREAMBLE OF THE MEL STATED THAT IT COVERED OPS CONDUCTED UNDER PARTS 121; 125; 135; ETC; BUT MADE NO REF TO PART 91. I ALSO RAN DOWN TO THE FAA FSDO ON THE FIELD; AND CAUGHT 2 OPS INSPECTORS AS THEY LEFT THEIR OFFICE. WHEN ASKED WHETHER I COULD OPERATE UNDER PART 91 PAST THE DEFERRAL PERIOD (10 DAYS); THEY WERE UNSURE; AND I LEFT THEM FEELING THAT IT WAS A GRAY AREA; BUT WILLING TO TAKE THE FLT. (THERE WAS NO QUESTION IN MY MIND THAT: 1) THE OP WOULD BE LEGAL WITHOUT AN MEL UNDER 91.213. 2) I WOULD CERTAINLY NOT BE PERMITTED TO OPERATE UNDER PART 135 UNDER THE CIRCUMSTANCES. 3) THAT THE ACFT WAS SAFE TO OPERATE. AFTER COMPLETING THE FLT; I DID MORE RESEARCH INTO THE SUBJECT AND FOUND IN ADVISORY CIRCULAR 91-67 PAGE 3; PARAGRAPH 6 (MEL RESTRS) A SPECIFIC REF TO 'COMPLIANCE WITH SUCH AN MEL IS MANDATORY; EVEN DURING PART 91 OPS.' THE CERTIFICATE HOLDER SHOULD HAVE ASKED OUR MAINT INSPECTOR FOR AN EXTENSION OF THE DEFERRAL; WHICH COULD HAVE EASILY BEEN GRANTED. I SHOULD HAVE TAKEN THE EXTRA TIME TO RESEARCH THE QUESTION; EVEN WITH PAX WAITING IN THE TERMINAL.