MEL vs MMEL: what is the difference?

What it means in practice

The MMEL sits at aircraft-type level. It is the master list that defines what equipment may be inoperative, under what conditions, and with what rectification interval logic, for the type design basis. The operator does not use the MMEL directly as a dispatch document unless the approval structure specifically permits that route. The operator uses its MEL.

The MEL is the operator-controlled implementation document. It reflects the operator’s aircraft configuration, routes, approvals, operating procedures, maintenance support, and any restrictions the operator or authority adds. That is why two operators on the same aircraft type can have different MELs while still drawing from the same MMEL logic.

Who it applies to

The distinction applies to operators, continuing airworthiness managers, dispatch, maintenance control, and certifying staff involved in deferred defects and dispatch decisions. It also matters to flight crew because the approved operational conditions, placards, procedures, and performance consequences come through the MEL actually in force for the operator.

It is especially relevant wherever INOP items, rectification intervals, or dispatch relief decisions are made. The quality of the MEL system directly affects dispatch legality and defect control.

What EASA says

Part-ORO requires the operator to establish a minimum equipment list where required and to base it on the relevant master source and approval framework. The current operational rule set places the MEL requirement in ORO.MLR.105, supported by AMC and GM, while the aircraft-type MMEL framework is supported through certification and MMEL policy material. The operator may be more restrictive than the MMEL but not less restrictive.

Common mistakes

The most common mistake is speaking as if the MEL and MMEL are the same document. They are not. One is the master basis. The other is the operator-approved implementation.

Another frequent mistake is misunderstanding rectification interval categories and their control logic. The item is not legally dispatchable because someone wrote "INOP" in the tech log. It is dispatchable only if the MEL, conditions, maintenance action, placarding, and interval control all permit that outcome.