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Minimum Equipment Lists (MEL): What Pilots and Aircraft Owners Need to Know

Updated: Dec 19, 2025

Aircraft systems occasionally fail or become inoperative, but that doesn’t always mean the aircraft is automatically grounded. The FAA provides a structured way to determine whether an aircraft can be legally and safely flown with certain inoperative equipment through a Minimum Equipment List (MEL).


Understanding how MELs work is essential for pilots, aircraft owners, and operators—especially those flying complex or commercially operated aircraft.



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What Is a Minimum Equipment List (MEL)?

A Minimum Equipment List (MEL) is an FAA-approved document that specifies which aircraft equipment may be inoperative and still allow the aircraft to be operated under specific conditions.


An MEL is:

  • Aircraft-specific (by make, model, and sometimes serial number)

  • Approved by the FAA

  • Legally binding once adopted by the operator


If an item is not listed in the MEL, it generally must be operational unless deferred under other regulatory provisions.


Why MELs Exist

MELs exist to balance:

  • Operational flexibility, and

  • Aviation safety


They prevent unnecessary aircraft grounding while ensuring that safety-critical systems remain functional. MELs are especially common in:

  • Commercial operations (Part 121 and 135)

  • Turbine aircraft

  • Complex general aviation aircraft


MEL vs. MMEL: What’s the Difference?

Master Minimum Equipment List (MMEL)

  • Created by the aircraft manufacturer

  • Approved by the FAA

  • Serves as a baseline template

  • Not legally usable by operators


Minimum Equipment List (MEL)

  • Derived from the MMEL

  • Customized for a specific aircraft and operator

  • Approved by the local FAA Flight Standards District Office (FSDO)

  • Legally enforceable


You cannot operate under an MMEL alone—you must have an approved MEL.


What an MEL Contains

A typical MEL includes:

  • A list of aircraft systems and components

  • Conditions and limitations for operating with an item inoperative

  • Required procedures (maintenance and operational)

  • Repair categories with time limits


Each item clearly states:

  • Whether it may be inoperative

  • Under what conditions

  • For how long


Required Procedures: (M) and (O)

Many MEL items include required procedures:

  • (M) Maintenance Procedures: Must be completed by qualified maintenance personnel before flight.

  • (O) Operational Procedures: Must be performed by the flight crew during operation.


Both procedures must be completed and documented for the MEL deferral to be valid.


Who Can Use an MEL?

An MEL is typically required for:

  • Part 121 and 135 operators

  • Some Part 91 operators who choose to adopt one


Private Part 91 operators are not required to have an MEL but may voluntarily adopt one if approved by the FAA.


Once an MEL is adopted, the operator must use it—you cannot switch back and forth between MEL rules and basic deferral rules.


What If You Don’t Have an MEL?

If an aircraft does not have an MEL, inoperative equipment may only be deferred under 14 CFR §91.213(d). This requires that:

  • The item is not required by regulation (91.205)

  • The item is not required by the aircraft’s POH/AFM

  • The item is not required by an Airworthiness Directive

  • The item does not affect safety

  • The item is deactivated, placarded, and documented


This is commonly referred to as “the four-step rule” for inoperative equipment.


MELs and Airworthiness

Operating contrary to an MEL:

  • Renders the aircraft unairworthy

  • Can result in FAA enforcement action

  • May invalidate insurance coverage


Pilots are responsible for understanding and complying with the MEL before every flight.


Common MEL Mistakes

  • Assuming an MEL is optional after adoption

  • Missing required (M) or (O) procedures

  • Exceeding repair time limits

  • Improper or missing placards

  • Incomplete maintenance log entries


These issues are frequently discovered during ramp checks and inspections.


Why MEL Knowledge Matters for Pilots

Understanding MELs helps pilots:

  • Make legal go/no-go decisions

  • Communicate effectively with maintenance

  • Avoid violations during inspections

  • Operate complex aircraft confidently


For student and transitioning pilots, MELs are also a common checkride and interview topic.


Final Thoughts

Minimum Equipment Lists provide a structured, safety-driven approach to managing inoperative equipment. Whether you’re flying under Part 91, 135, or 121, understanding how MELs work is essential to maintaining airworthiness and regulatory compliance.

Pilots who truly understand MELs are better decision-makers—and safer operators.



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