What is a Minimum Equipment List (MEL)?

An MEL is an operator‑specific document derived from the aircraft type’s MMEL that lists equipment which may be inoperative for dispatch while maintaining safety. It defines repair categories, procedures, and limitations.

What is a Part 91 MEL (LOA D195)?

For Part 91/125, the FAA issues LOA D195 authorizing use of an MEL—typically tail‑specific and accepted by the FSDO/IFO—referencing the operator’s MEL and procedures manual.

What is a Part 135 MEL (OpSpec D095)?

For Part 121/135 air carriers, OpSpec D095 accepts the operator’s MEL for listed aircraft, enabling legal deferral per MEL limitations and repair categories under the certificate holder’s program.

What are MEL repair categories B, C, and D?

Repair categories limit the deferral interval: B = 3 days, C = 10 days, D = 120 days (Category A as specified). Operators must track due dates to avoid overflying limits.

What is the difference between MMEL and MEL?

The MMEL is a master document approved for the aircraft type; the MEL is a customized, operator‑specific document based on the MMEL with procedures and limitations tailored to the operator’s configuration.

What are NEF and CDL in relation to the MEL?

NEF (Non‑Essential Furnishings) covers interior cosmetic or convenience items; CDL (Configuration Deviation List) covers missing exterior items affecting performance. They complement the MEL and are managed separately.

Minimum Equipment List (MEL) for Part 91 (LOA D195) & Part 135 (OpSpec D095)

What is it?

What is an MEL?

The Minimum Equipment List (MEL) enables the dispatch of an aircraft in a condition that ensures both safety and airworthiness, even when a specific system, functions, or equipment may be temporarily unavailable or inoperative.

Operational Flexibility

Maintains revenue-earning operations without compromising flight safety.
Allows deviation from the type certificate requirement of 100% functional equipment.

Key Limitations Without MEL

Without the document, Air Carriers cannot deviate from the type certificate of the aircraft.
Requires all equipment to be 100% functional, limiting operational adaptability, in other words, you can not apply 91.205 logic to a Part 135 operation.

MEL's Strategic Role and Operational Impact

The MEL’s intent is not to grant permission to fly a broken or un-airworthy airplane to skirt around required maintenance. It is simply a method to safely defer the maintenance to another time to allow for relocation of the aircraft, parts to be delivered, and work to be scheduled, all without interrupting revenue service.

Part 91 vs Part 135

Part 91 MEL (LOA D195/D095)

For Part 91 operations, LOA D195 authorizes use of your custom, tail-specific MEL. LOA D195 is the only internationally recognized Part 91 MEL. LOA D095 authorize the operator to use a generic MMEL for their operation. For U.S. operators limited to domestic operations, this LOA is the more cost effective and faster option. However, the lack of tail specificiity makes the deferral process longer and possibly more complex.

Part 135 MEL (OpSpec D095)

For Part 135 air carriers, OpSpec D095 is the only option for an MEL. OpSpec D095 is tail-specific and custom made to your exact operation. This OpSpec can also exist as a fleet MEL where one document covers your entire type fleet

Key Concepts

MMEL vs MEL vs NEF vs CDL

MMEL is the FAA‑approved master equipment list for the type. MEL is your operator‑specific list tailored to configuration. NEF addresses interior non‑essential furnishings such as coffee-makers. CDL addresses external items affecting performance such as fairings and wheel covers. This list is often part of the Aircraft Flight Manual (AFM), Aircraft Maintenance Manual (AMM), or Manufacturer Supplementary Manual. These documents complement each other.

MEL Repair Categories

Deferred items must be repaired within their category limits: A = Manufacturer-specified, B = 3 days, C = 10 days, D = 120 days. Additional limitations may be imposed based on distance and/or number of cycles.

Example

Example MEL ATA Table

Issues

Common Compliance Issues

Addressing compliance issues in aircraft operations is paramount for ensuring safety and regulatory adherence. The points below highlight these common pitfalls, offering insights to enhance operational compliance and safety.

Keeping records and closely monitoring the due dates of each deferred item is vital. Updates should be made daily to the aircraft status sheet to ensure compliance and to avoid overflying any required maintenance. Many maintenance software on the market today automate the process and provide alerts.
One often neglected aspect of deferring items is forgetting to adjust the aircraft equipment suffix on the Flight Plan. Dispatchers and Pilots should understand the applicable suffix to each aircraft. For example, a differed autopilot system will mean that flight into RVSM is prohibited, and thus, the “W” suffix must be removed from Block 10 of the ICAO flight plan.
Another common issue stems from failing to understand aircraft systems and systems' interconnectivity. New aircraft are very complex machines, and seemingly unrelated systems can drastically affect each other. For example, a Radar Altimeter is connected to the aircraft’s E-GPWS system, which may be connected to the auto-throttle system and the weight-on-wheels sensor. Although you may be allowed to defer the two systems independently, it is imperative to understand the specific aircraft systems, as you might not be able to defer two interconnected systems if they are inoperative simultaneously.
Write ups. The FAA continues to audit for poor, inaccurate, or completely missing maintenance write-ups; an issue that very much plagues the industry. A common problem with MEL usage is pilots see that an item is deferrable, assume that it carries no safety risk to fly with it inoperative, and fail to create a maintenance discrepancy write-up. This practice is illegal and goes against basic safety management concepts. For some operators that perform CASS (Continuing Analysis and Surveillance System), proper documentation and tracking of equipment is vital, as it ensures the aircraft receives the proper maintenance it needs.

MEL Order Form

Fill out the request form, and someone from our team will reach out for a quote. We will follow up with an additional questionnaire specific to your aircraft type.

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