DHC8 CREW FLEW THE ACFT WITH INCOMPATIBLE MEL ITEMS.

Narrative

ACFT WAS FLOWN WITH INCOMPATIBLE MEL'S. 1 MEL WAS INOP AUTOPLT AND THE OTHER WAS INOP ALT SELECTOR. THE 2 MEL'S ARE NOT USUALLY THOUGHT OF AS BEING INTERCONNECTED (ALTHOUGH THEY APPARENTLY ARE). THE ACFT HAD BEEN SIGNED OFF AND RELEASED BY MAINT WITH NUMBERS ASSIGNED TO EACH MEL (WHICH SHOULD NOT HAVE HAPPENED). AND THE ACFT WAS FLOWN BY SEVERAL OTHER CREWS BEFORE THE PROB WAS FOUND OUT. THE BREAKDOWN STARTED WITH MAINT AND CONTINUED WITH THE FLC'S. THE FLC'S WERE SLOW TO PICK UP ON IT DUE TO THE FACT THAT THE MEL'S HAD BEEN APPROVED AND THE MEL'S ARE RELATIVELY MINOR AND NOT READILY SEEN AS BEING CONNECTED WITH EACH OTHER. WHEN LOOKING AT THE MAINT LOG I WAS CHKING TO SEE THAT THE WRITE-UPS THEMSELVES WERE DONE CORRECTLY (WHICH THEY WERE) AND TO SEE IF THE INOP STICKERS WERE IN THE RIGHT PLACE AND THAT THERE WERE NO ASSOCIATED PERFORMANCE PENALTIES. I ALSO CHKED THE SUPPLEMENT CHART WHICH SHOWS WHICH MEL'S ARE COMPATIBLE WITH DIFFERENT ACFT OPS (IE; MEL FOR ANTI-SKID BRAKES INVALIDATES THE SUPPLEMENT THAT ALLOWS OP IN TAILWINDS 10-20 KTS). WE DON'T HAVE AN MEL CHART WHICH I THINK WOULD HAVE HELPED A GREAT DEAL IN AVOIDING THIS INCIDENT AND KEEP IT FROM HAPPENING AGAIN.