CRJ200 CREW DEPARTS WITH TWO MEL'S THAT ARE NOT COMPATIBLE; RESULTING IN THE LOSS OF #2 HYD SYSTEM.

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THE CAPT TOOK A LOOK THROUGH THE ACFT'S MEL BOOK. THE AIRWORTHINESS RELEASE WAS SHOWING 2 DEFERRED MAINT ITEMS ON THIS FLT. THE DEFERRED MAINT ITEMS WERE CONCERNING A GENERATOR ON THE #1 ENG AND AN ENG DRIVEN HYD PUMP ON THE #2 ENG. THE GENERATOR HAD BEEN DEFERRED BEFORE THE PREVIOUS FLT FROM INDIANAPOLIS; IN. THE GENERATOR DEFERRAL REQUIRED THE ACFT TO HAVE AN OPERABLE ELECTRIC HYD PUMP ON THE #2 SYS. THIS REQUIREMENT WAS MET. THE HYD DEFERRAL REQUIRED THAT THE ELECTRIC HYD PUMP FOR SYS #2 BE RUN CONTINUOUSLY INFLT. THE CAPT PERFORMED THE NECESSARY OPERATIONAL PROCS FOR THE DEFERRALS; STOWED THE MEL BOOK AND CONTINUED WITH HIS PREFLT DUTIES. ON TKOF FROM BOS ARPT; THE FLT CREW EXPERIENCED A HYD SYS #2 LOW PRESSURE CAUTION MESSAGE. THE CREW PERFORMED THE QRH PROC AND WAS UNABLE TO RESOLVE THE MESSAGE. THE CREW CONTINUED ON THEIR FPR AND CONTACTED THEIR MAINT CTL AND DISPATCH TO GET FURTHER INFO ABOUT THE REASON WHY THEIR ACFT WAS EXPERIENCING NO HYD PRESSURE IN THE #2 SYS. THE QRH DIRECTED THE CREW TO LAND AT THE NEAREST SUITABLE ARPT; SO AN ARPT WAS CHOSEN TO ALLOW FOR ADEQUATE FUEL BURN TO BRING THE ACFT BELOW ITS LNDG WT OF 47000 LBS. NO EMER WAS DECLARED AND THE LNDG WAS PERFORMED BY THE FO. ON POST FLT; THE CAPT AND THE DISPATCHER READ THROUGH THE DEFERRED MAINT ITEMS AND FOUND THAT THE MEL FOR THE ENG DRIVEN HYD PUMP REQUIRED BOTH ENG GENERATORS TO BE OPERATIONAL. THE CAPT THEN REMEMBERED THAT THE LOAD SHEDDING LOGIC OF THE GENERATORS SHUTS DOWN THE CROSS SIDE ELECTRIC HYD PUMP. THIS IS WHY THE #2 ELECTRIC PUMP WAS UNABLE TO OPERATE INFLT. AT THIS TIME; THE REALIZATION THAT THE PREVIOUS CREW HAD OPERATED THE ENTIRE FLT TO BOSTON WITH NO HYD PRESSURE IN SYS #2 BECAME APPARENT. THE CAPT ALLOWED THE ERRORS FROM THE PREVIOUS CREW AND STATION MAINT ROLL OVER ONTO THIS FLT AND FAILED TO CATCH THE PROB BEFORE TKOF. DURING PREFLT THE CAPT ASSUMED THAT SINCE THE ACFT HAD OPERATED FROM INDIANAPOLIS TO BOSTON THAT IT WAS AIRWORTHY AND DID NOT READ THROUGH THE MEL BOOK AS CLOSELY AS HE SHOULD HAVE.