How to use a Minimum Equipment List (MEL) and a Configuration Deviation List (CDL).

Bottom line

The MEL serves as a reference guide for dispatchers and pilots to determine whether takeoff of an aircraft with inoperative instruments or equipment is authorized under applicable regulatory requirements. A CDL is used in the same manner as an MEL, but it addresses missing external parts of the aircraft rather than failing internal systems and their constituent parts. The MEL only applies while the aircraft sits on the ground awaiting departure or takeoff; once airborne, any mechanical failures should be addressed using the appropriate checklists and approved AFM, not the MEL.