CAPT OF CL60 SERIES ACFT LEARNS THAT HIS COMPANY MAINT PERSONNEL HAVE IMPROPERLY DEFERRED A MFD AND CONVINCED HIM TO MAKE AN INAPPROPRIATE LOGBOOK ENTRY VERIFYING THE CONDITION MET WITH THE APPROPRIATE MEL.

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WHILE PREPARING FOR A PART 135 FLT FROM ZZZ TO DTW; OUR COMPANY SCHEDULING CALLED TO INFORM US THAT OUR ACFT WAS GNDED FOR AN UNKNOWN MAINT PROB. WE WERE TOLD TO CONTINUE PREFLTING OUR CHALLENGER 604; JUST IN CASE THE PROB WAS RESOLVED IN TIME TO DO THE TRIP. AT XA30; OUR PAX ARRIVED. SCHEDULING INFORMED US THAT WE WERE 99% SURE THAT WE COULD DO THE TRIP; AFTER THE APPROPRIATE WRITE-UPS AND DEFERRALS WERE MADE. I WAS CONTACTED BY OUR MAINT CTL DEPT. MAINT CTL INFORMED ME THAT THE MFD #2 WAS REPLACED RECENTLY WITH AN IMPROPER PART NUMBER. THEY CONTACTED THE MANUFACTURER AND APPARENTLY GAINED APPROVAL TO DEFER THE MFD #2 UNTIL THE PROPER PART NUMBER COULD BE INSTALLED WITHIN THE NEXT 3 DAYS. MAINT CTL THEN TOLD ME 'WORD-FOR-WORD' HOW TO WRITE UP AND DEFER THIS ITEM. I FAXED THEM A COPY OF THE WRITE-UP; AND THEY AGREED THAT EVERYTHING WAS CORRECT. BY XA48; WE WERE READY TO DEPART; AND SUCCESSFULLY COMPLETED THE FLT. ENRTE; I CHKED THE MEL TO VERIFY MY WRITE-UP AND DEFERRAL; BUT COULD NOT FIND AN ENTRY FOR MFD DEFERRALS. THE MEL NUMBER GIVEN TO ME BY MAINT CTL WAS A REF TO ED1 AND ED2 (EICAS DISPLAY) DEFERRALS. AFTER LNDG; I CALLED THEM; BUT THEY SAID THAT EVERYTHING WAS CORRECT. I ASSUMED THEY HAD A SPECIAL WAIVER FROM THE MANUFACTURER OR THE FAA; SINCE THERE WAS ALSO A REF TO BOMBARDIER IN THE DEFERRAL. THE NEXT DAY WE FLEW ANOTHER 2 LEGS; ENDING AT OUR HOME BASE. I SPOKE WITH ONE OF OUR LINE MECHS; WHO WAS VERY KNOWLEDGEABLE ABOUT THE CL604. HE ALSO BELIEVED THAT MFD'S WERE NOT DEFERRABLE. I CALLED MAINT CTL AGAIN; BUT AGAIN THEY SAID THAT THE #2 MFD WAS DEFERRABLE. I MET WITH OUR CHIEF PLT TUESDAY MORNING TO EXPRESS MY CONCERNS (AND DISTRUST) FOR MAINT CTL. AFTER FURTHER INVESTIGATION; IT TURNED OUT THAT I WAS CORRECT; AND I HAD LET MAINT CTL TALK ME INTO MAKING AN INAPPROPRIATE DEFERRAL. IN MY RUSH TO COMPLETE THE FLT; I TRUSTED THEIR EXPERTISE TO HELP ME WITH THE WRITE-UPS. BUT IF I HAD TAKEN THE TIME TO DOUBLECHK IT; I MAY HAVE CAUGHT THEIR ERROR.