Introduction
Typical all commercial aircraft are designed and certified with a significant amount of equipment redundancy, and as a result it can be demonstrated that the airworthiness requirements are satisfied by a substantial margin.
It may also be the case that some equipment which is fitted to the aircraft is not actually required for safe operation under all operating conditions, e.g. instrument lighting in day VMC.
Other equipment, such as entertainment systems or galley equipment, may be installed only for passenger convenience.
If it is the case that this non-safety related equipment does not affect the airworthiness or operation of the aircraft when inoperative, it is not required to be listed in the MMEL/MEL or for that matter to be given a rectification interval.
However, in the case that the “non-safety” related equipment has a safety related function for example the use of the entertainment system for passenger briefings – then this item must be included in the MMEL/MEL with an appropriate rectification interval.
MEL Purpose
The MEL is a joint operations and maintenance document prepared by an operator to:
Identify the minimum equipment and conditions for an aircraft to maintain the Certificate of Airworthiness in force and to meet the operating rules for the type of operation;
Define operational procedures necessary to maintain an acceptable level of safety and to deal with inoperative equipment; and
Define maintenance procedures necessary to maintain an acceptable level of safety and procedures necessary to secure any inoperative equipment.
MEL Definition
Essentially the MMEL is for intended for a specific aircraft type, whilst the MEL is tailored to the operator’s specific aircraft and operating environment.
The MEL may also be tailored to suit specific route networks as well as, geographic location, and to also consider the various operational bases and spares capacity at these bases. (The MMEL cannot address these individual variables, nor standard terms such as “As required by Operational Requirements”. It is for this reason that an MMEL is not accepted by the Authority as a substitute for the MEL.)
The operator is responsible to develop operational “(O)” and maintenance “(M)” procedures, or to require the use of other Type Certificate Holder provided documentation, for example Dispatch Deviations Guide (DDG).
MEL Intent
Operation of an aircraft with aircraft equipment inoperative or removed is prohibited, unless an operator does so in compliance with an approved MEL or specific regulatory approval.
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