MELs

MEL stands for Minimum Equipment List. It is a defined, aircraft-specific document that authorizes the operation of an aircraft with certain equipment inoperative under predefined conditions. The MEL is derived from the master minimum equipment list (MMEL) published by the aircraft manufacturer and is approved by the relevant national aviation authority. The MMEL is standardized guidance, while the operator’s MEL adapts it to a specific aircraft type and operator.

The purpose of an MEL is to permit continued flight with reduced capabilities when certain equipment is not operational, rather than grounding the aircraft for every failure. It specifies what may be inoperative, under what circumstances, and for how long, as well as any required procedures or alternate means of operation. The document helps balance safety with operational efficiency, ensuring that critical systems remain available or that approved procedures are followed when a system is not functioning.

Regulatory framework varies by country but follows a common principle: the MEL is approved by the national aviation authority and is used in conjunction with the MMEL. In the United States, for example, the MEL is part of the operator’s operations specifications and must align with FAA-approved guidance. Similar processes exist under EASA and other authorities, often with a DMEL (domestic MEL) or equivalent for cross-border operations. Any deviation from the MMEL or changes to an MEL require regulatory review and approval.

Contents typically include item numbers, affected equipment, conditions for inoperability, time limits for dispatch (A, B, C, or D times), required actions by maintenance and crew, and any dispatch restrictions or alternate procedures. The MEL is used by flight crews, maintenance personnel, and operations control to determine eligibility for flight with inoperative equipment.