AN EMBRAER 120 WAS DISPATCHED WITH A GENERATOR SYS DEFERRED INOP PER THE MEL BUT IN CONFLICT WITH AN AIRWORTHINESS DIRECTIVE.

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THE PROB I ENCOUNTERED OCCURRED ON 3 REVENUE ACR FLTS I DISPATCHED ON JUL/XZ/98. THE FLTS IN QUESTION WERE ACR XYZ; YYX; AND XZZ. THE FLTS WERE OPERATED UNDER FAR PART 121. THE PROB STEMS FROM A LIMITATION OF THE ACFT BEING ADDED DUE TO AN AIRWORTHINESS DIRECTIVE ON THE ACFT (THE BRASILIA E120); BUT NOT REFLECTED IN THE MEL. AN AIRWORTHINESS DIRECTIVE WAS ISSUED FOR THE ACFT; AND CONCERNED A LOAD-SHEDDING PROB WITH THE ELECTRICAL SYS WHEN 1 GENERATOR WAS LOST WHILE THE ACFT WAS IN ICING CONDITIONS AND THE DEICING EQUIP WAS OPERATING. THE AIRWORTHINESS DIRECTIVE REQUIRED A MODIFICATION OF THE ACFT; BUT ALLOWED RELIEF TO OPERATE THE ACFT UNDER CERTAIN LIMITATIONS UNTIL THE MODIFICATIONS COULD BE MADE. ADDED TO THE LIMITATIONS SECTION OF THE ACFT'S FLT STANDARDS MANUAL FOR UNMODIFIED ACFT WAS 'BOTH STARTER/GENERATORS MUST OPERATE NORMALLY PRIOR TO FLT.' THE MEL; HOWEVER; WAS NOT UPDATED; AND UNDER MEL ALLOWS FOR DEFERRAL OF '1 GENERATOR FUNCTION' PROVIDED SOME LISTED CONDITIONS WERE MET. MAINT DEFERRED 1 GENERATOR PRIOR TO DEP OF FLT XYZ. THE CREW CALLED ME TO ADVISE ME OF THE MEL ADDED TO THE ACFT; AND I CONSULTED THE MEL AND DETERMINED THAT THE DEFERRAL WAS A LEGAL DEFERRAL; AND ALL OF THE PROVISIONS WERE MET. ONLY AFTER THE 3 REVENUE FLTS WERE COMPLETED WAS I MADE AWARE OF THE LIMITATION OF THE ACFT WHICH HAD BEEN ADDED AS A TEMPORARY REVISION TO THE FLT STANDARDS MANUAL. THEREFORE; THE FLTS WERE OPERATED WITH AN ILLEGAL DEFERRAL. THE PROB HERE OBVIOUSLY IS THE CONFLICTING INFO BTWN THE FLT STANDARDS MANUAL AND THE MEL. AS DISPATCHERS; WE REFER TO THE MEL CONTINUOUSLY TO DETERMINE AN ACFT'S AIRWORTHINESS FOR REVENUE PART 121 OPS. I BELIEVE THAT WHEN A LIMITATION IS ADDED TO AN ACFT; THE MEL SHOULD BE UPDATED AT THE SAME TIME TO REFLECT COMPLIANCE WITH THE LIMITATION.