Definition
An FAA-approved document, issued for a specific aircraft make and model, that identifies the instruments and equipment which may be inoperative while still allowing the aircraft to be operated safely under defined conditions and limitations. The MMEL is produced by the FAA in cooperation with the manufacturer and serves as the master template from which an operator develops its own aircraft-specific Minimum Equipment List (MEL).
Plain English
It is the FAA's master list, written for a particular aircraft type, showing which items can be broken or missing and the aircraft is still legal and safe to fly, along with the rules that apply when something is inoperative. Operators use this master list as the starting point for the customized list they actually use day to day.
Context Anchor
Seen when discussing whether an aircraft can legally fly with certain equipment not working, especially in Minimum Equipment List procedures.
Derivation
"Master" is used in the sense of an authoritative source document from which other versions are derived. "Minimum" indicates the lowest acceptable level of working equipment. Together the term signals that this is the FAA's top-level reference list of the least amount of equipment that must work for safe operation.
Why Pilots Care
It provides the legal basis to operate an aircraft with certain equipment inoperative rather than grounding the plane unnecessarily.
Intuition Check
Do not treat the word “master” as meaning “ready to use for every airplane.” Here, “master” means it is the main FAA-approved source used to build a more specific approved list.
Example Sentence 1
The operator's MEL was developed directly from the MMEL issued by the FAA for that aircraft model.
Example Sentence 2
According to the MMEL, the flight could proceed with one fuel gauge unserviceable provided the tanks were verified full by another method.