from the MEL:
For the sake of brevity, the MEL does not include all the obviously required items such as wings, rudders, flaps, engines, landing gear, etc. or any structural damage.
However, some of the obviously required items are included to remove any doubts regarding their importance of their being operative.
The MEL does not include items which do not affect the airworthiness if the aircraft such as galley equipment, entertainment systems, passenger convenience items, etc.
It is important to note that;
“ALL ITEMS WHICH ARE RELATED TO THE AIRWORTHINESS OF THE AIRCRAFT AND ARE NOT INCLUDED ON THE LIST ARE REQUIRED TO BE OPERATIVE AT ALL TIMES”.
Exceptions are items which have serviceability specifications contained in the manufacturer's Aircraft Maintenance Manual (AMM), Structural Repair Manual (SRM) or other approved manufacturer's manual/drawings. In this case Engineering will advise dispatchability of such items with the relevant extracts from AMM, SRM or other approved manufacturer's manual/drawings.