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Minimum Equipment Lists (MELs)

Procedures

Can you fly without an MEL? Is an MMEL good enough? Under Part 91, do you have to comply with the time intervals? The answers aren't as clear cut as you might think.


 

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Photo: An inoperative fire loop "MEL'd" on Eddie's aircraft.

Why Things Aren't as Straight Forward as They Could Be

It all starts with two paragraphs in 14 CFR 91 and then FAA Order 8900 puts in a few good words before your local FSDO puts in its own spin. When you get done with all that, you need to worry about ICAO Annex 6, Part I (if you are commercial) or Part II (if you are not). Too many questions? Here are a few:

You might note the answer is given for the first question: it depends. Well, guess what? That is the answer to the other questions too.

If something isn't working, can I fly?

Before December 1988 operating under 14 CFR 91, if something wasn't working, you had to get it repaired in accordance with Part 43. But that has changed.

[14 CFR 91, ¶91.405] Each owner or operator of an aircraft—

  1. Shall have that aircraft inspected as prescribed in subpart E of this part and shall between required inspections, except as provided in paragraph (c) of this section, have discrepancies repaired as prescribed in part 43 of this chapter;
  2. Shall ensure that maintenance personnel make appropriate entries in the aircraft maintenance records indicating the aircraft has been approved for return to service;
  3. Shall have any inoperative instrument or item of equipment, permitted to be inoperative by §91.213(d)(2) of this part, repaired, replaced, removed, or inspected at the next required inspection; and
  4. When listed discrepancies include inoperative instruments or equipment, shall ensure that a placard has been installed as required by §43.11 of this chapter.

[14 CFR 43, ¶43.11(b)] For those items permitted to be inoperative under §91.213(d)(2) of this chapter, that person shall place a placard, that meets the aircraft's airworthiness certification regulations, on each inoperative instrument and the cockpit control of each item of inoperative equipment, marking it “Inoperative,” and shall add the items to the signed and dated list of discrepancies given to the owner or lessee.

Now, if something isn't working, you can have it repaired, replaced, or removed or inspected at the next required inspection, provided that is permitted by: 14 CFR 91, ¶91.213. This is a long, convoluted work of art. I'll highlight what is important to this question and get back to the other portions when they come up. But the entire paragraph is presented here for reference.

[14 CFR 91, ¶91.213]

(a) Except as provided in paragraph (d) of this section, no person may take off an aircraft with inoperative instruments or equipment installed unless the following conditions are met:

(1) An approved Minimum Equipment List exists for that aircraft.

. . . AND . . .

(2) The aircraft has within it a letter of authorization, issued by the FAA Flight Standards district office having jurisdiction over the area in which the operator is located, authorizing operation of the aircraft under the Minimum Equipment List. The letter of authorization may be obtained by written request of the airworthiness certificate holder. The Minimum Equipment List and the letter of authorization constitute a supplemental type certificate for the aircraft.

(3) The approved Minimum Equipment List must—

(i) Be prepared in accordance with the limitations specified in paragraph (b) of this section; and

(ii) Provide for the operation of the aircraft with the instruments and equipment in an inoperable condition.

(4) The aircraft records available to the pilot must include an entry describing the inoperable instruments and equipment.

(5) The aircraft is operated under all applicable conditions and limitations contained in the Minimum Equipment List and the letter authorizing the use of the list.

(b) The following instruments and equipment may not be included in a Minimum Equipment List:

(1) Instruments and equipment that are either specifically or otherwise required by the airworthiness requirements under which the aircraft is type certificated and which are essential for safe operations under all operating conditions.

(2) Instruments and equipment required by an airworthiness directive to be in operable condition unless the airworthiness directive provides otherwise.

(3) Instruments and equipment required for specific operations by this part.

(c) A person authorized to use an approved Minimum Equipment List issued for a specific aircraft under subpart K of this part, part 121, 125, or 135 of this chapter must use that Minimum Equipment List to comply with the requirements in this section.

. . . EXCEPT . . .

(d) Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations conducted under this part with inoperative instruments and equipment without an approved Minimum Equipment List provided—

(1) The flight operation is conducted in a—

(i) Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air aircraft, powered parachute, or weight-shift-control aircraft, for which a master minimum equipment list has not been developed; or

(ii) Small rotorcraft, nonturbine-powered small airplane, glider, or lighter-than-air aircraft for which a Master Minimum Equipment List has been developed; and

(2) The inoperative instruments and equipment are not—

(i) Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated;

(ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted;

(iii) Required by §91.205 or any other rule of this part for the specific kind of flight operation being conducted; or

(iv) Required to be operational by an airworthiness directive; and

(3) The inoperative instruments and equipment are—

(i) Removed from the aircraft, the cockpit control placarded, and the maintenance recorded in accordance with §43.9 of this chapter; or

(ii) Deactivated and placarded “Inoperative.” If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with part 43 of this chapter; and

(4) A determination is made by a pilot, who is certificated and appropriately rated under part 61 of this chapter, or by a person, who is certificated and appropriately rated to perform maintenance on the aircraft, that the inoperative instrument or equipment does not constitute a hazard to the aircraft.

An aircraft with inoperative instruments or equipment as provided in paragraph (d) of this section is considered to be in a properly altered condition acceptable to the Administrator.

(e) Notwithstanding any other provision of this section, an aircraft with inoperable instruments or equipment may be operated under a special flight permit issued in accordance with §§21.197 and 21.199 of this chapter.

So if you are flying a turbine powered aircraft or one that has an MMEL, you must have an MEL.

But are there exceptions?

Yes, but it is a fairly narrow list:

[14 CFR 91, ¶91.213 (d)]

Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations conducted under this part with inoperative instruments and equipment without an approved Minimum Equipment List provided—

(1) The flight operation is conducted in a— (i) Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air aircraft, powered parachute, or weight-shift-control aircraft, for which a master minimum equipment list has not been developed; or (ii) Small rotorcraft, nonturbine-powered small airplane, glider, or lighter-than-air aircraft for which a Master Minimum Equipment List has been developed; and

(2) The inoperative instruments and equipment are not— (i) Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated; (ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted; (iii) Required by §91.205 or any other rule of this part for the specific kind of flight operation being conducted; or (iv) Required to be operational by an airworthiness directive; and

(3) The inoperative instruments and equipment are— (i) Removed from the aircraft, the cockpit control placarded, and the maintenance recorded in accordance with §43.9 of this chapter; or (ii) Deactivated and placarded “Inoperative.” If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with part 43 of this chapter; and (4) A determination is made by a pilot, who is certificated and appropriately rated under part 61 of this chapter, or by a person, who is certificated and appropriately rated to perform maintenance on the aircraft, that the inoperative instrument or equipment does not constitute a hazard to the aircraft.

An aircraft with inoperative instruments or equipment as provided in paragraph (d) of this section is considered to be in a properly altered condition acceptable to the Administrator.

(e) Notwithstanding any other provision of this section, an aircraft with inoperable instruments or equipment may be operated under a special flight permit issued in accordance with §§21.197 and 21.199 of this chapter.

So yes, there are exceptions. But if you are operating a turbine-powered airplane or one with an MMEL, you are not an exception and will need an MEL.

Is an MMEL good enough?

Developing your own MEL can be expensive and the manufacturer's MMEL might be all you really need. Can you do that? Yes, but let's understand the differences first.

What's the Difference Between an MMEL and an MEL?

[FAA Order 8900, Volume 4, Chapter 4, ¶4-658]

  • Master minimum equipment list. An MMEL contains a list of items of equipment and instruments that may be inoperative on a specific type of aircraft (e.g., BE-200, Beechcraft model 200). It is also the basis for the development of an individual operator’s MEL.
  • I think of an MMEL as coming from the manufacturer, covering a broader range of aircraft that just yours.

  • Minimum equipment list. The MEL is the specific inoperative equipment document for a particular make and model aircraft by serial and registration numbers, e.g., BE-200, N12345. A part 91 MEL consists of the MMEL for a particular type aircraft, the preamble for part 91 operations, the procedures document, and an LOA. The FAA considers the MEL as an STC. As such, the MEL permits operation of the aircraft under specified conditions with certain equipment inoperative.

[FAA MMEL Policy Letter 34, Preamble] The MMEL is the basis for development of individual operator MELs which take into consideration the operator's particular aircraft equipment configuration and operational conditions. Operator MELs, for administrative control, may include items not contained in the MMEL; however, relief for administrative control items must be approved by the Administrator. An operator's MEL may differ in format from the MMEL, but cannot be less restrictive than the MMEL. The individual operator's MEL, when approved and authorized, permits operation of the aircraft with inoperative equipment. Equipment not required by the operation being conducted and equipment in excess of 14 CFR requirements are included in the MEL with appropriate conditions and limitations. The MEL must not deviate from the Aircraft Flight Manual Limitations, Emergency Procedures or with Airworthiness Directives. It is important to remember that all equipment related to the airworthiness and the operating regulations of the aircraft not listed on the MMEL must be operative.

I think of an MEL as something you are responsible for putting together (with our without) the manufacturer's help. It covers specific aircraft.

You can use the MMEL as an MEL, however . . .

[FAA Order 8900, Volume 4, Chapter 4, ¶4-661] The regulations require that all equipment installed on an aircraft in compliance with the airworthiness standards and operating rules be operative. The FAA-approved MMEL includes those items of equipment and other items which the FAA finds may be inoperative and yet maintain an acceptable level of safety. The MMEL does not contain obviously required items such as wings, flaps, rudders, etc. When a part 91 operator uses an MMEL as an MEL, all instruments and equipment not covered in the MMEL must be operative at all times regardless of the operation conducted, unless:

  • They are newly installed and are not a safety of flight item such as a terminal collision avoidance system (TCAS), an extra piece of navigational equipment, a wind shear detection device, a ground proximity warning system, a radar altimeter, passenger convenience items, etc.;
  • The operator has developed appropriate procedures for disabling or rendering them inoperative; and
  • The operator has contacted the FSDO having oversight within 10 calendar-days following an installation and requested in writing that the equipment be added to the MMEL.

So if you are just talking about operating in the United States and you are okay with the fact everything in your specific airplane that isn't addressed in the more general MMEL must be working (for the most part), then you are good to go. Except . . .

Is an MEL ever mandatory?

If you fly internationally, unless every country you plan on visiting has an exception to the following paragraphs to ICAO Annex 6, I believe you are required to have an MEL unless you are flying non-commercially and your aircraft does not have an MMEL established.

ICAO Annex 6, Part II, applies to all general aviation aircraft operating internationally.

[ICAO Annex 6, Part II, ¶3.6.1.1] Where a master minimum equipment list (MMEL) is established for the aircraft type, the operator shall include in the operations manual a minimum equipment list (MEL) approved by the State of Registry of the aeroplane which will enable the pilot-in-command to determine whether a flight may be commenced or continued from any intermediate stop should any instrument, equipment or systems become inoperative.

[ICAO Annex 6, Part II, Attachment 3.B]

  1. If deviations from the requirements of States in the certification of aircraft were not permitted, an aircraft could not be flown unless all systems and equipment were operable. Experience has proved that some unserviceability can be accepted in the short term when the remaining operative systems and equipment provide for continued safe operations.
  2. The State should indicate through approval of a minimum equipment list those systems and items of equipment that may be inoperative for certain flight conditions with the intent that no flight can be conducted with inoperative systems and equipment other than those specified.
  3. A minimum equipment list, approved by the State of the Operator, is therefore necessary for each aircraft, based on the master minimum equipment list established for the aircraft type by the organization responsible for the type design in conjunction with the State of Design.
  4. The State of the Operator should require the operator to prepare a minimum equipment list designed to allow the operation of an aircraft with certain systems or equipment inoperative provided an acceptable level of safety is maintained.

ICAO Annex 6, Part I, applies to all commercial aviation aircraft operating internationally.

[ICAO Annex 6, Part I, ¶6.1.3] The operator shall include in the operations manual a minimum equipment list (MEL), approved by the State of the Operator which will enable to pilot-in-command to determine whether a flight may be continued from any intermediate stop should any instrument, equipment or systems become inoperative. Where the State of the Operator is not the State of Registry, the State of the Operator shall ensure that the MEL does not affect the aeroplane's compliance with the airworthiness requirements applicable in the State of Registry.

[Wynbrandt]

  • U.S. Part 91 twin turboprops and jets flown in Europe must now operate with a Minimum Equipment List (MEL) developed for that specific aircraft under Letter of Authorization (LOA) D195, rather than with a manufacturer’s aircraft model Master MEL (MMEL) approved by the FAA under LOA DO95. Laurent Chapeau, head of the ramp inspection office of the French Safety Oversight Authority, which administers SAFA ramp inspections for third-country operators in France, has affirmed EASA’s recent recognition of the ICAO standard.
  • “The regulation is now clearly written from last November,” Chapeau said, adding that his agency has noted a lack of compliance “during ramp inspections in the last few months.” In some cases, inspectors “did raise Category 2 findings,” which represent “significant impact on safety” and require operators to take follow-up preventive action.
  • Under ICAO guidelines, LOA DO95 doesn’t provide the oversight or approval process required for a valid MEL. FAA Flight Standards is reportedly developing compliance solutions for affected U.S. operators. The U.S. is the sole ICAO signatory country that allows operators to use an MMEL as an MEL.

So if you are operating internationally, you need an MEL and an MMEL isn't good enough. If you are flying a U.S. registered aircraft, that MEL is issued to Part 91 operators under LOA D195. If you are operating under LOA D095, you have an "MMEL used as an MEL" and that is not good enough to operate internationally.

. . . under Part 91 are the Repair Category Intervals mandatory?

Now that you have an MEL and the authorization to use it, do you have to comply with those repair intervals that you've heard only apply to commercial operators?

[FAA Order 8900, Volume 4, Chapter 4, ¶4-658. B. 13)] The Flight Standards District Office (FSDO) issues a letter of authorization (LOA) to an operator when the FSDO authorizes an operator to operate under the provisions of an MEL. Together, the LOA, the procedures document (paragraph 4-658B(22)), and the MMEL constitute a supplemental type certificate (STC). The operator must carry the STC in the aircraft during its operation.

I've heard some people say an MEL is advisory for us who operate under Part 91 but that isn't true. 14 CFR 91, ¶91.213 tells us the MEL and the LOA authorizing the MEL are mandatory for those of us operating turbine-powered airplanes. FAA Order 8900, Volume 4, Chapter 4, ¶4-658. B. 13) tells us that these become part of an STC and must be carried on the aircraft. So if your MEL specifies repair intervals and doesn't give you an exception, you must comply with them. An FAA Policy Letter spells this out:

[FAA MMEL Policy Letter 25, ¶24.] . 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):

  1. 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, hours, etc.), repair tracking begins at the point when the malfunction is deferred in accordance with the operator’s approved MEL.
  2. 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.
  3. 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.
  4. 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.

So, even operating under Part 91, you must comply with the repair intervals.

There is another view of this, however. Some interpret everything under the "Repair Category" section to be the repair category and the "provisos" everything in the columns to the right. I've asked a PMI who disagrees. But it has also been pointed out that if you ask 20 FAA inspectors for an opinion you will get 21 answers. (I once worked with a POI who said, "The FAA is comprised of 78 Flight Standards District Offices, each independently owned and operated.") So what to do? My advice: treat the repair intervals as applicable, that is the conservative approach. If you want to interpret the regulations more liberally, ask your PMI to be sure.

References

14 CFR 43, Title 14: Maintenance, Preventative Maintenance, Rebuilding, and Alteration, Federal Aviation Administration, Department of Transportation

14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation

FAA Orders 8400 and 8900

FAA MMEL Policy Letter 25, Revision 20 GC, December 17, 2012

FAA MMEL Policy Letter 34, Revision 4, August 15, 1997

FAA MMEL Policy Letter 36, Revision 2, August 15, 1997

FAA MMEL Policy Letter (PL)106, Revision 5 GC, June 6, 2014

ICAO Annex 6 - Operation of Aircraft - Part 2 General Aviation, International Standards and Recommended Practices, Annex 6 to the Convention on International Civil Aviation, Part II, 8th edition, July 2014

Wynbrandt, James, "EASA: U.S. Operators Can't Use MMEL in Europe," AIN online, March 28, 2017

Revision: 20170401
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