Minimum Equipment List for Aircraft Operations

by Admin on November 14, 2022

In accordance with Federal Aviation maintenance Regulations, aircraft operators must have all equipment installed on their aircraft maintenance and repair operative at the time of flight. The Minimum Equipment List (MEL) is a document and method for obtaining relief from this requirement. This document specifies which parts of an aircraft may be inoperable, along with the procedures that must be followed for the aircraft maintenance technology to function under specific circumstances.

MELs are developed based on Master Minimum Equipment Lists (MMELs), produced by aircraft manufacturers. Each operator develops their MEL in accordance with their specific equipment, instrumentation, and operational conditions based on the MMEL.

Requirement of the Regulation

In Title 14 CFR section 91.205, aircraft maintenance and repair equipment and instruments are listed that must be installed, as well as whether the equipment and instruments are operable. In section 91.213 of Part 91, the use of an FAA-approved MEL permits aircraft to operate with inoperable instruments and equipment, which is a relief from section 91.205. Additionally, the regulation specifies which instruments and equipment are not permitted in MELs.

Operational and Maintenance Procedures for MEL

MEL limits the duration and conditions of operation with inoperative equipment in order to maintain an acceptable level of safety and reliability. Aircraft maintenance records/logbooks must be updated when inoperative equipment is discovered, according to regulations. Prior to further operation of the item, an appropriately certificated aircraft maintenance technician deactivates and placards it in accordance with the MEL or other approved means acceptable to the FAA and air transport association.

Every step necessary to accomplish an operation or aviation maintenance technology task must be specified in the “O” and “M” procedures.

  • In planning and/or operating with an inoperative item, the “O” symbol indicates the need to perform a specific operation. It is usually the flight crew that performs these procedures; however, other personnel may be qualified and authorized to handle them as well.
  • When the “(M)” symbol appears, it indicates the item must undergo a specific maintenance procedure before it can be operated. Most of these procedures are carried out by maintenance personnel; however, other personnel may be qualified and authorized to do so.


Repair Intervals

It consists of a number of repair interval categories A, B, C, and D. Users of a MEL approved under Parts 91K, 121, 125, 129, and 135 must repair inoperable systems or components at or before the repair times established by the following letter designations:

Category A

MEL approved by the certificate holder must specify in the remarks column the time interval for repairing this category item.

Category B

Repairs on this category item must be completed within three consecutive calendar days (72 hours), excluding the day on which it was noted in the aircraft maintenance record.

Category C

A maintenance record or logbook of the aircraft maintenance and repair needs to be maintained within 10 consecutive calendar days (240 hours), excluding the day on which the malfunction was noticed.

Category D

An aircraft maintenance technology log and/or record recording the malfunction must be maintained within 120 consecutive calendar days (2880 hours), excluding the day the malfunction was recorded.

How the MEL Approval Process Works?

POI (principal operations inspector) or operations inspector completes the review and approval of MEL in collaboration with the corresponding principal aviation maintenance technology and principal avionics inspectors. As specified in operations specification (OpSpec)/management specification (MSpec) D095, Minimum Equipment List (MEL) Authorization, the principal maintenance inspector is responsible for evaluating and approving a certificate holder’s MEL Management Program. Operators operating under Part 91 receive the same FAA flight technician; however, they issue a Letter of Authorization (LOA) rather than an operation specification.

Responsibility of The Operators

A manufacturer’s aircraft flight and maintenance manual, manufacturer’s recommendations, flight technician, engineering specifications, and the manufacturer’s recommendations should be used by the operator to develop and submit Operations (O) and Maintenance (M) procedures to the FAA and air transport association.

Upon determining that the proposed MEL is complete and contains all required information, the POI will begin reviewing the package. In most cases, this is where problems begin for operators. Despite the inspector’s duty to compare the MEL with the MMEL, the review or analysis process can be frustrating and challenging.

MEL management program issues frequently focus on “O” and “M” procedures, deferral and parts management, or the duration of deferrals. The inspector may be delayed despite FAA and air transport association guidance telling him or her to conduct a timely review. MELs may remain in an FAA and air transport association office unattended for more than a year, despite complaints from industry operators.

How iJET Handles Minimum Equipment Lists (MELs)

A Minimum Equipment List is a documentation process affecting aircraft operators directly. As part of its expert operator team, iJET carefully monitors all the processes involved in aircraft maintenance and conducts all flights in a safe and approved manner.

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