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MMEL – MEL – Minimum Equipment Lists & Definitions

Aviation GlossaryA Master Minimum Equipment List (MMEL) is developed by the Type Certificate holder, approved by the governing authority and adopted by an Aircraft  Operator in a customized MEL in order provide flexibility by continuing to operate an aircraft even when certain items or systems are inoperative.

The Master Minimum Equipment List (MMEL) includes those items of equipment related to airworthiness, operating requirements and other items of equipment which may be inoperative and yet maintain an acceptable level of safety by appropriate conditions and limitations; it does not contain obviously required items such as wings, flaps, and rudders.

The Master Minimum Equipment List (MMEL) is the basis for development of individual operators’ MELs which take into consideration the operator’s particular aircraft equipment configuration and operating environments. An operator’s MEL may differ in format from the Master Minimum Equipment List (MMEL) but cannot be less restrictive than the Master Minimum Equipment List (MMEL).

The individual operator’s MEL, when approved, permits operation of the aircraft with inoperative equipment. Equipment not required by the operation being conducted and equipment in excess of operational requirements are included in the MEL with appropriate conditions and limitations.

The MEL must not deviate from Airworthiness Directives or any other Mandatory Requirement. It is important to remember that all equipment related to the airworthiness and the operating requirements of the aircraft not listed in the Master Minimum Equipment List (MMEL) must be operative.

Suitable conditions and limitations in the form of placards, maintenance procedures, crew operating procedures and other restrictions as necessary are specified in the MEL to ensure that an acceptable level of safety is maintained.

The MEL is intended to permit operation with inoperative items of equipment for a period of time until rectifications can be accomplished. It is important that rectifications be accomplished at the earliest opportunity. In order to maintain an acceptable level of safety and reliability the Master Minimum Equipment List (MMEL) establishes limitations on the duration of and conditions for operation with inoperative equipment.

The MEL provides for release of the aircraft for flight with inoperative equipment. When an item of equipment is discovered to be inoperative, it is reported by making an entry in the Aircraft Maintenance Record/Logbook. The item is then either rectified or may be deferred per the MEL or other approval means prior to further operation.

MEL conditions and limitations do not relieve the operator from determining that the aircraft is in a condition for safe operation with items of equipment inoperative and is airworthy.

MEL – Minimum Equipment List Related Definitions that may be used by Aircraft Operators developing their MEL

The following definitions will be used in MMELs. For an individual operator’s MEL, certain MMEL definitions may be edited and/or not required. MEL definitions, including format issues, will be tailored, as appropriate, dependent upon the aircraft operator’s make/model of aircraft, type of installed instrument and equipment items, and specific operation. However, the intent of the definition must be the same and cannot be less restrictive than the MMEL. See FAA Order 8900.1, Volume 4, Chapter 4 for further information.

To access the Master Minimum Equipment List for individual Aircraft from the FAA follow this link

1. Accessible Lavatory Items

Under 14 CFR § 382.63, accessible lavatory items include: ability to enter lavatory and maneuver by means of on-board wheelchair. The lavatory shall provide door locks, accessible call buttons, grab bars, faucets, other controls, and dispensers.Air Carriers must maintain all aircraft accessibility features in proper working order, per 14 CFR § 382.71. The accessible lavatory requirement, in part, applies to aircraft with more than one isle in which lavatories are provided per § 382.63(a). Aircraft operators are not required to retrofit cabin interiors of existing aircraft to comply with the requirements of § 382.63.

2 . Administrative Control Item (ACI)

An ACI is listed by the aircraft operator in the MEL for tracking and informational purposes. As an example, ACI may be used to track ETOPS accomplishment of required APU cold-soak, or in-flight verification starts. An ACI may be added to an aircraft operator’s MEL by approval of the POI provided no relief is granted, or provided conditions and limitations are contained in an approved document (e.g., Structural Repair Manual (SRM) or Airworthiness Directive (AD)). If relief other than that granted by an approved document is sought for an ACI, a request must be submitted to the Administrator. If the request results in review and approval by the FOEB, the item becomes an MMEL item rather than an ACI.

3. ATA System Page

The ATA system page is divided into four (4) columns and contains: item and repair category; number installed; number required for dispatch; and remarks or exceptions. Standard ATA categories are used. Items are numbered sequentially.

  • Item.
  • Repair Category. See definition #24.
  • Number Installed. This column depicts the number (quantity) of instrument and equipment items normally installed in the aircraft. This number represents the aircraft configuration considered in developing this MMEL. Should the number be a variable (e.g., fleet configuration differences, cockpit lighting items, cabin lighting items, cargo restraint components) a number is not required and the “-” symbol is used.
  • Number Required for Dispatch. This column depicts the minimum number (quantity) of instrument and equipment items required for operation provided the conditions specified in the “Remarks or Exceptions” column are met. Where the MMEL shows a variable number required for dispatch, the MEL must reflect the actual number required for dispatch or an alternate means of configuration control approved by the Administrator.
  • Remarks or Exceptions . This column may include a statement(s) either prohibiting or permitting operation with a specific number of instrument and equipment items inoperative, provisos (conditions and limitations) for such operation, and appropriate notes.
  • Provisos. Provisos are indicated by a number or a lower case letter in “Remarks or Exceptions”. Provisos are conditions or limitations that must be complied with for operation with the listed instrument or equipment item inoperative.
  • Notes. Notes provide additional information for crewmember or maintenance consideration. Notes are used to identify applicable material, which is intended to assist with compliance, but do not relieve the aircraft operator of the responsibility for compliance with all applicable requirements. Additional notes may be amended, deleted, or added to the MEL by the aircraft operator, as appropriate. Notes are not a part of the provisos.
  • Vertical Bar (change bar). A vertical bar indicates a change, addition, or deletion in the adjacent text for the current revision of that page only. All change bars applicable to the previous revision of the MMEL are removed prior to the release of the next revision.

4. Airplane Flight Manual (AFM), Rotorcraft Flight Manual (RFM)

The FAA-approved AFM/RFM is the document approved by the responsible FAA Aircraft Certification Office (ACO) during type certification. The approved flight manual for the specific aircraft is listed on the applicable Type Certificate Data Sheet (TCDS). The approved flight manual is the source document for operational limitations and performance parameters for an aircraft. The term “approved flight manual” can apply to either an AFM or an RFM. The FAA requires an approved flight manual for aircraft type certification.

5. As Required by 14 CFR

When the MMEL states, “As Required by 14 CFR,” the listed instrument or equipment item is subject to certain provisions (restrictive or permissive) expressed in the 14 CFR operating rules. The number of items required by 14 CFR must be operative. When the listed item is not required by 14 CFR, it may be inoperative for the time specified by repair category. The term “14 CFR” has replaced “FAR” as the current reference to Federal Regulations pertaining to aviation. However, many, if not most, MMELs still contain the acronym “FAR”; therefore, this acronym is acceptable and retained in PL-025 and this definition.

6. Code of Federal Regulations (CFR) and Federal Aviation Regulations (FAR)

CFR, the current term, and FAR both refer to the applicable portions of the Federal Aviation Act and Code of Federal Regulations.

7. Considered Inoperative

The phrase, “Considered Inoperative”, as used in the provisos, means that an instrument and equipment item must be treated for dispatch, taxi and flight purposes as though it were inoperative. The item will not be used or operated until the original deferred item is repaired. Additional actions include: documenting the item on the dispatch release (if applicable), placarding, and complying with all remarks, exceptions, and related MMEL provisions, including any (M) and (O) procedures and observing the repair category.

8 . Continuing Authorization – Single Extension

An aircraft operator who has the authorization to use an FAA-approved MEL may also have the authority to use a continuing authorization to approve a single (one-time) extension to the repair interval for category B or C items in accordance with Operations Specification D095. Continuing Authorization – Single Extensions are not authorized for repair category A and D items.

9. Dash (-)

Indicates a variable number (quantity) of the instrument and equipment items may be installed or required for dispatch. This is common when a fleet MEL is used since aircraft of the same make and model may have differing numbers of specific instrument and/or equipment items installed.

10. Day of Discovery

This is the calendar-day an equipment/instrument malfunction was recorded in the aircraft maintenance record/logbook. This day is excluded from the calendar-days or flight-days specified in the MMEL for the repair interval of an inoperative instrument and/or equipment item. This provision is applicable to all MMEL items; i.e., categories A, B, C, and D.

11. Deactivated and/or Secured

When the MMEL refers to an instrument and/or equipment item as deactivated and/or secured, the specified component must be put into an acceptable condition for safe flight. An acceptable method of deactivating and/or securing will be established by the aircraft operator.

12. Deleted

“Deleted” in the remarks column after a sequence item indicates that the item was previously listed but is now required to be operative if installed in the aircraft.

13. Extended Range Operations (ER)

ER refers to extended range operations (ETOPS) of an airplane with operational approval to conduct ETOPS in accordance with the applicable regulations.

14. Excess Items

Excess items are those instrument and equipment items that have been installed that are redundant to the requirements of the 14 CFR.

15. Flight Day

A flight-day is a 24-hour period (from midnight to midnight) either universal coordinated time (UTC) or local time, as established by the aircraft operator, during which at least one flight is initiated for the affected aircraft.

16. Heavy Maintenance Visit (HMV)

HMV is a scheduled C-check/D-check or airworthiness maintenance program inspection where the aircraft is scheduled to be out of service for 4 or more days.

17. Icing Conditions

An atmospheric environment that may cause ice to form on the aircraft (structural) or in the engine(s) (induction).

18. Inoperative

A system and/or component malfunction to the extent that it does not accomplish its intended purpose and/or is not consistently functioning normally within its approved operating limit(s) and/or tolerance(s).

19. Inoperative Components of an Inoperative System

Inoperative instrument and equipment items, which are components of a system that is inoperative, are usually considered components directly associated with and having no other function than to support that system (warning/caution systems associated with the inoperative system must be operative unless relief is specifically authorized per the MMEL).

20. Is Not Used

The phrase “Is Not Used” in the provisos, remarks or exceptions for an MMEL instrument or equipment item may specify that another item in the MMEL “is not used”. In such cases, crewmembers must not activate, actuate, or otherwise utilize that item under normal operations. It is not necessary for aircraft operators to accomplish the (M) procedure(s) associated with the item. However, operational requirements must be complied with, and an additional placard must be affixed, to the extent practical, adjacent to the control or indicator for the item that is not used. This informs crewmembers that an instrument or equipment item is not to be used under normal operations.

21. Nonessential Equipment and Furnishings (NEF)

NEFs are those items installed on the aircraft as part of the original type certification (TC), STC, engineering order, or other form of alteration that have no effect on the safe operation of flight and would not be required by the applicable certification rules or operational rules. They are those items that, if inoperative, damaged, or missing, have no effect on the aircraft’s ability to be operated safely under all operational conditions. NEF items are not instrument and equipment items already identified in the MEL or CDL of the applicable aircraft. They do not include instrument and equipment items that are functionally required to meet the certification rule or for compliance with any operational rule.

22. Operative

An operative system and/or component will accomplish its intended purpose and is consistently functioning normally within its design operating limit(s) and tolerance(s). When an MMEL item specifies that an item of equipment must be operative, it does not mean that it’s operational status must be verified; it’s to be considered operative unless reported or known to be malfunctioning. When an MMEL item specifies that an item of equipment must be verified operative, it means that it must be checked and confirmed operative at the interval(s) specified for that MMEL item. When an MMEL item specifies that an item of equipment must be verified but no interval is specified, verification is required only at the time of deferral.
Other terminology sometimes used interchangeably with “operative” within the MMEL is “operates normally”, “fully operative”, and “considered operative”. The aircraft operator’s MEL may incorporate standardized terminology of the aircraft operator’s choice to specify that an item of equipment must be operative, provided the aircraft operator’s MEL definitions indicate that the selected “operative” terminology means that the required item of equipment will accomplish its intended purpose and is consistently functioning normally within its design operating limit(s) and tolerance(s).

23. Placarding

Each inoperative instrument or equipment item must be placarded to inform and remind the crewmembers and maintenance personnel of the item condition. To the extent practical, placards should be located adjacent to the control or indicator for the item affected; however, unless otherwise specified (i.e. AFM), placard wording and location will be determined by the aircraft operator.

24. Repair Category

All users of an MEL approved under parts 91K, 121, 125, 129, 135 and 142 must effect repairs of inoperative instrument and equipment items, deferred in accordance with the MEL, at or prior to the repair times established by the following letter designators. Part 91 MEL users (D095/D195 LOAs) are not required to comply with the repair categories, but will comply with any provisos defining a repair interval (flights, flight legs, cycles, hours, etc):

  • Repair Category A.

    This category item must be repaired within the time interval specified in the “Remarks or Exceptions” column of the aircraft operator’s approved MEL. For time intervals specified in “calendar days” or “flight days”, the day the malfunction was recorded in the aircraft maintenance record/logbook is excluded. For all other time intervals (i.e., flights, flight legs, cycles, hors, etc.), repair tracking begins at the point when the malfunction is deferred in accordance with the operator’s approved MEL.

  • Repair Category B.

    This category item must be repaired within 3 consecutive calendar-days (72 hours) excluding the day the malfunction was recorded in the aircraft maintenance record/logbook. For example, if it were recorded at 10 a.m. on January 26th, the 3-day interval would begin at midnight the 26th and end at midnight the 29th.

  • Repair Category C.

    This category item must be repaired within 10 consecutive calendar-days (240 hours) excluding the day the malfunction was recorded in the aircraft maintenance record/logbook. For example, if it were recorded at 10 a.m. on January 26th, the 10-day interval would begin at midnight the 26th and end at midnight February 5th.

  • Repair Category D.

    This category item must be repaired within 120 consecutive calendar-days (2880 hours) excluding the day the malfunction was recorded in the aircraft maintenance record/logbook.

25. Takeoff

Takeoff is the act of beginning a flight in which an aircraft is accelerated from a state of rest to that of flight. For the purposes of MEL relief, this translates to the point at which the pilot physically begins to apply power to initiate the takeoff from the runway or takeoff surface.
26. Triple Asterisk (***). Indicates an item which is not required by regulation but which may have been installed on some models of aircraft covered by this MMEL. This item may be included on the aircraft operator’s MEL after the approving office has determined that the item has been installed on one or more of the aircraft operator’s aircraft. The symbol, however, must not be carried forward into the aircraft operator’s MEL. It should be noted that neither this policy nor the use of this symbol provides authority to install or remove an item from an aircraft.

27. Visible Moisture

An atmospheric environment containing water, in any form, that can be seen in natural or artificial light; for example, clouds, fog, rain, sleet, hail, or snow.

28. Visual Flight Rules (VFR)

VFR is as defined in 14 CFR Part 91. This precludes a pilot from filing an Instrument Flight Rules (IFR) flight plan.

29. Visual Meteorological Conditions (VMC)

VMC means the atmospheric environment is such that would allow a flight to proceed under the visual flight rules applicable to the flight. This does not preclude operating under Instrument Flight Rules.

30. (M )

This symbol indicates a requirement for a specific maintenance procedure which must be accomplished prior to operation with the listed item inoperative. Normally, these procedures are accomplished by maintenance personnel; however, other personnel may be qualified and authorized to perform certain functions. Procedures requiring specialized knowledge or skill, or requiring the use of tools or test equipment, should be accomplished by maintenance personnel. The satisfactory accomplishment of all maintenance procedures, regardless of who performs them, is the responsibility of the aircraft operator. Appropriate procedures are required to be produced as part of the aircraft operator’s manual or MEL.

31. (O)

This symbol indicates a requirement for a specific operations procedure which must be accomplished in planning for and/or operating with the listed item inoperative. Normally, these procedures are accomplished by the flightcrew; however, other personnel may be qualified and authorized to perform certain functions. The satisfactory accomplishment of all procedures, regardless of who performs them, is the responsibility of the aircraft operator. Appropriate procedures are required to be produced as a part of the aircraft operator’s manual or MEL.

32. Electronic Fault Alerting System

New generation aircraft display system fault indications to the flight crew by use of computerized display systems. Aircraft manufacturers incorporate individual design philosophies when determining the data that is represented. The following are customized definitions (specific to each manufacturer) to help determine the level of messages affecting the aircraft’s dispatch status.

A. AIRBUS (A300-600, A310, A318/319/320/321, A330, A340, A380)

Airbus aircraft equipped with Electronic Centralized Aircraft Monitoring (ECAM) provide different levels of system condition messages {WARNING (red), CAUTION (amber)}. On A318/319/320/321, A330 and A340, the ECAM STATUS page also provides MAINTENANCE STATUS messages. Any message that affects airplane dispatch is displayed at the WARNING or CAUTION level. For A318/319/320/321, MAINTENANCE STATUS messages may also affect airplane dispatch. System faults that result only in messages on the Central Maintenance System (CMS) (for A330, A340 and A380) or on the Centralized Fault Display System (CFDS) (for A318/319/320/321) do not affect airplane dispatch and do not require action other than as addressed within the aircraft operator’s standard maintenance program.
B. BOEING (B-717, MD-10, MD-11)

These aircraft are equipped with an alerting function which is a subsystem within the Electronic Instrument System (EIS). The alerting function provides various levels of system condition alerts (WARNING, CAUTION, ADVISORY, MAINTENANCE and STATUS). Alerts that affect aircraft dispatch will include WARNING, CAUTION, STATUS or MAINTENANCE level. MAINTENANCE alerts are displayed on the status page of the EIS display panel under the maintenance heading. A MAINTENANCE alert on the EIS indicates the presence of a system fault which can be identified by the Central Fault Display System (CFDS) interrogation. The systems are designed to be fault tolerant, however, for any MAINTENANCE alert, the MEL must be verified for dispatch purposes.

C. BOEING (747-400, 747-8, 757, 767, 777, 787)

Boeing airplanes equipped with Engine Indicating and Crew Alerting Systems (EICAS) provide different priority levels of system messages (WARNING, CAUTION, ADVISORY, STATUS and MAINTENANCE). Any messages that affect airplane dispatch status will be displayed at a STATUS message level or higher. The absence of an EICAS STATUS or higher level (WARNING, CAUTION, ADVISORY) indicates that the system/component is operating within its approved operating limits or tolerances. System conditions that result only in a maintenance level message, i.e. no correlation with a higher level EICAS message, do not affect dispatch and do not require action other than as addressed within an aircraft operator’s standard maintenance program.

D. CANADAIR (CL-65, CL-604)

Canadair aircraft equipped with Engine Indication and Crew Alerting Systems (EICAS) provide four classes of messages (WARNING, CAUTION, ADVISORY, and STATUS). Any message that affects aircraft dispatch will be at the WARNING, CAUTION, or STATUS level. System conditions that only require maintenance are not visible to the flight crew. These maintenance indications/messages are only activated by maintenance personnel using the Maintenance Diagnostics Computer.

E. De-HAVILLAND (DASH 8 SERIES 400)

Series 400 aircraft are equipped with a Caution/Warning Panel that annunciates all cautions and warnings. Advisory messages are displayed by the Electronic Indication System (EIS) or individual advisory lights supplied in the cockpit. “Class 1 failures” are failures that prevent continued operation of a specific Line Replacement Unit or channel and are annunciated via advisory messages: caution, warning or advisory lights in the flight compartment. Dispatching with such posted failures are to be in accordance with the MMEL. “Class 2 failures” are failures which do not prevent continued system function. These faults will not be annunciated to the flight crew and the absence of the higher level alert (warning, caution, advisory) indicates that the system/component is operating within its approved operating limits or tolerances. Such faults would be evident during maintenance interrogation performed during maintenance activities. Class 2 faults do not affect dispatch and will be listed in the Fault Isolation Manual (FIM). Class 2 faults will be left to the discretion of the aircraft operators when these faults are to be rectified.

F. EMBRAER (EMB-135/145, ERJ-170/190 Series)

The EMB-135/145 and ERJ-170/190 are equipped with an Engine Indicating and Crew Alerting System (EICAS) that provides three different message levels: WARNING, CAUTION, and ADVISORY. The ERJ-170/190 Series add STATUS messages. Failures that effect dispatchability are presented to the flight crew at one of these levels. Other failures may be presented only to the maintenance personnel on the Multi Function Display (MFD) maintenance pages or through the download of the Central Maintenance Computer (CMC). System conditions that result only in a maintenance level message, i.e. no correlation with a higher level EICAS message, do not affect dispatch and do not require action other than as addressed within an aircraft operator’s standard maintenance program.

G. FOKKER (FK-100)
Fokker aircraft are equipped with Multi Function Display System (MFDS) which provides electronic message referring to the different priority levels of system information (WARNING (red), CAUTION (amber), AWARENESS (cyan) AND STATUS (white). Any messages that affect aircraft dispatch will be at the WARNING, CAUTION or AWARENESS level. In these cases, the MEL must be verified for dispatch capability and maintenance may be required. System conditions that only require maintenance are not presented on the flight deck. These maintenance indications/messages may be presented on the Maintenance & Test Panel (MAP) or the Centralized Fault Display Unit (CFDU) and by dedicated Built-In Test Evaluation (BITE) of systems.
H. GULFSTREAM G-IV, G-V, GV-SP,GIV-X, GVI

Gulfstream airplanes equipped with EICAS provide different priority levels of system messages: WARNING (red), CAUTION (amber), and ADVISORY (cyan or blue). ADVISORY messages are further classified into STATUS, INFORMATION, and MAINTENANCE messages. Any WARNING or CAUTION message affects airplane dispatch status and requires that the AFM and MEL be used to determine dispatch capability. ADVISORY STATUS messages that indicate a system failure (e.g., FMS 1 fail) require that the AFM and MEL be used to determine dispatch capability. ADVISORY INFORMATION messages (e.g., Cockpit Phone Call) and MAINTENANCE messages (i.e., includes the words ‘Maintenance Required’ in the text of the message) do not affect airplane dispatch capability. ADVISORY MAINTENANCE messages indicate the presence of a system fault which can be identified by Maintenance Data Acquisition Unit (MDAU on the G-V) interrogation, Central Maintenance Computer (CMC on the GV-SP/GIV-X/VI) interrogation or by reference to the Airplane Flight Manual.

I. GULFSTREAM G-150, G-200

Gulfstream airplanes equipped with EICAS provide different priority levels of system messages: WARNING (red), CAUTION (amber), ADVISORY (green), and STATUS (white). The Airplane Flight Manual prohibits take off with any WARNING message displayed. CAUTION, ADVISORY and STATUS messages may affect airplane dispatch status and requires the Airplane Flight Manual or the MEL be used to determine dispatch capability. The airplane may dispatch with CAUTION, ADVISORY and STATUS messages that indicate proper system operation and are not illuminated due to a system failure (i.e. FUEL STBY PUMP ON when the pump is selected ON, GND A/B OUT with LAND selected on the ground, or APU GEN OFF with the switch OFF). MAINTENANCE and MAINTENANCE DATA STATUS messages do not affect airplane dispatch status. They indicate the presence of a system fault which can be retrieved from the Maintenance Diagnostics Computer. In all cases, the Airplane Flight Manual must be referenced and procedures compiled with for the displayed message prior to applying MEL dispatch relief.

J. GULFSTREAM G280

Gulfstream airplanes equipped with EICAS provide different priority levels of system messages: WARNING (red), CAUTION (amber), ADVISORY and MAINTENANCE (cyan or blue), and STATUS (white). Any WARNING or CAUTION message affects aeroplane dispatch status and requires that the Aeroplane Flight Manual or the MEL be used to determine dispatch capability. ADVISORY messages which indicate a system failure (e.g., FMS 1 fail) require that the Aeroplane Flight Manual or the MEL be used to determine dispatch capability. MAINTENANCE messages do not affect aeroplane dispatch status. They indicate the presence of a system fault which can be identified by Onboard Maintenance System (OMS) interrogation or by reference to the Aeroplane Flight Manual. STATUS messages do not affect the dispatch status. They indicate the status of a system.

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