Minimum Equipment List (MEL) and Inoperable Instruments

Minimum Equipment List (MEL) and Inoperable Instruments


Background

Until changes were made to 14 CFR 91.213 many years ago, the Minimum Equipment List (MEL) concept only applied to air carrier or commercial operations and general aviation operators of multiengine aircraft for which the FAA had developed a Master Minimum Equipment List (MMEL).

Regulation previously required that all aircraft discrepancies occurring between inspections had to be repaired in accordance with 14 CFR Part 43 before the aircraft could be operated. This meant that all the aircraft's instruments and equipment, regardless of whether they were essential or not to the flight operation being conducted, had to be operative. Often, this requirement placed a burden on the operators.

The FAA recognized this burden and initiated several rulemaking projects that have resulted in the present-day wording of 14 CFR 91.205 and 91.213, which permit the operator to operate an aircraft with certain instruments and equipment inoperative and to have the maintenance on those items deferred.

Pilots need to be comfortable with their understanding of 14 CFR 91.213, but the Minimum Equipment List concept seems to complicate the situation unnecessarily.

To help answer some of the commonly asked questions on this topic, we have provided a list of definitions and FAQs to provide you a better understanding.

Definitions

Equipment List. An inventory of equipment installed by the manufacturer or operator on a particular aircraft.

Kinds of Operations List (KOL). The KOL specifies the kinds of operations (e.g., visual flight rules [VFR], instrument flight rules [IFR], day, or night) in which the aircraft can be operated. The KOL also indicates the installed equipment that may affect any operating limitation. (Although the certification rules require this information, there is no standard format; consequently, the manufacturer may furnish it in various ways).

Letter of Authorization (LOA). The flight standards district office (FSDO) issues an LOA to an operator when the FSDO authorizes an operator to operate under the provisions of an MEL. Together, the LOA, the procedures document, and the MMEL constitute a supplemental type certificate (STC). The operator must carry the STC in the aircraft during its operation. If a fractional ownership is involved, the LOA will be issued to the management company. Each individual owner will not be listed in the LOA.

Master Minimum Equipment List (MMEL). 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). Notice that this does not include a specific aircraft by registration number. This is the basis for the development of an individual operator's MEL.

Minimum Equipment List (MEL). The MEL is the specific inoperative equipment document for a particular make and model aircraft by serial and registration numbers. For example, PA 28-181, N12345. A Part 91 MEL consists of the Master Minimum Equipment List (MMEL) for a particular type aircraft, the preamble for Part 91 operations the procedures document, and a Letter of Authorization (LOA). The FAA considers the MEL as a supplemental type certificate (STC). As such, the MEL permits operation of the aircraft under specified conditions with certain equipment inoperative.

Operator. Refers to an individual or company. For this discussion, only refers to Part 91 operations.

Placard. A decal or label with letters at least 1/8-inch high. The operator or mechanic must place the placard on or near inoperative equipment or instruments so that it is visible to the pilot or flight crew and alerts them to the inoperative equipment.

Small Aircraft. Means an aircraft with a maximum certificated takeoff weight of 12,500 pounds or less.

Frequently Asked Questions

What, exactly, is a Minimum Equipment List?

An MEL is defined in Advisory Circular 91-67 as a precise listing of instruments, equipment, and procedures that allows an aircraft to be operated under specific conditions with inoperative equipment.

An MEL is part of an FAA authorization that allows for the operation of an aircraft from other than the provisions of 14 CFR 91.213 that regulates inoperative instruments and equipment. FAA flight standards district offices have listings of generic MELs for various models of aircraft; these are called master MELs (MMELs). An operator or pilot can get a copy of the master MEL for his model aircraft and customize it according to his particular instruments and equipment. With FAA detailed review and approval of his document by N number, an FAA Letter of Authorization (LOA) can be granted, giving the authority to operate under the provisions of the MEL.

The value of an MEL lies in the fact that pilot judgment is removed; this can be comforting to the commercial operator who wants every one of his pilots and/or renters to make the same decision but frustrating to the individual without options. As one example, let's say the attitude indicator is to be required on all VFR flights.

You can probably see that the pilot operating under 14 CFR 91.213 instead of an MEL would have the flexibility to decide for himself about the attitude indicator on a VFR day. Although he may agree that at a 1,500-foot ceiling and 3 miles visibility he wants the attitude indicator, at clear and 20, he would hate to be restricted from flying, as the pilot under the MEL in this case would be. It's difficult to think of every scenario ahead of time to write it into an MEL.

The possible value of the MEL to the private operator lies in the safety of already having something on paper ahead of time so that the FAA couldn't question the operator's judgment and research skills.

Our suggestion to owners and operators is that they should create a file containing the original certification minimum equipment data, a copy of the aircraft's type certificate document, and a photocopy of 14 CFR 91.205 (day/night/VFR/IFR equipment). These can all be photocopied to a few 8.5 x 11-inch pages that could be easily kept in the aircraft.

If my airplane has an approved MEL, do I have to use it?

Yes. If your airplane has an approved MEL, then the MEL must be used rather than the provisions of 91.213(d). If the provisions of 91.213 are used, the approved MEL and Letter of Authorization must be surrendered to the appropriate flight standards district office.

Am I required to have an MEL to take off with inoperative instruments or equipment?

You may take off with inoperative instruments and equipment without having an MEL only if your aircraft doesn't have an existing MEL or Letter of Authorization and the inoperative instruments or equipment meet the following criteria:

Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air aircraft, powered parachute, or weight-shift-control aircraft, for which a master MEL has not been developed; or small rotorcraft, non-turbine-powered small aircraft, gliders, and lighter-than-air aircraft for which a master MEL has been developed, may fly with inoperative instruments and equipment as long as the item(s) are not one of the following four:

  1. Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated. Examples might be: a fuel indicator, oil pressure gauge, magnetic compass, or a cylinder head temperature gauge requirement. Note: This document may not differ from item 3 below, but it could contain additional equipment.
  2. Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List (KOL) for the kind of flight operation being conducted. An example might be, very specifically, the stall warning horn on a 1970 Cessna 150, as listed on the aircraft type certificate. For kinds of operations, this is referring to VFR, IFR, day, or night in which the aircraft can be operated.
  3. Required by 14 CFR 91.205 or any other rule of this part (14 CFR Part 91) for the specific kind of flight operation being conducted. Example: FAR 91.205 lists day and night VFR and IFR equipment.
  4. Required to be operational by an airworthiness directive; and
    1. The inoperative instruments and equipment are removed from the aircraft, the cockpit control placarded, and the maintenance recorded in accordance with 14 CFR 43.9; or
    2. Deactivated and placarded "Inoperative." If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded, and the pilot or mechanic can determine that the inoperative instrument or equipment does not constitute a hazard to the aircraft.

Notwithstanding any other provision of 14 CFR 91.213, an aircraft with inoperative instruments or equipment may be operated under a special flight permit, or ferry permit.

Why would someone want to get an MEL if they can operate without it under 91.213?

While it is true that operating under 91.213 might be less burdensome on the operator, some aircraft operators choose to operate under an MEL to better suit a particular operation. For example, if an aircraft is used under Part 91 but also operating under leaseback to a Part 135 operation, the operator might decide to operate the aircraft under an MEL. The MEL might be more restrictive than 91.213 or an MMEL.

How do I get an MEL?

You will need to schedule an appointment with your local FSDO to meet with an airworthiness inspector. The FSDO inspector will provide you an MMEL and other pertinent documentation that will help you develop your MEL.

The FSDO inspector will discuss the differences between operating under 91.213(d) and operating with an MEL to be certain that you understand what you're getting involved in.

After the FSDO inspector discusses the operator's responsibilities when operating with an MEL, and the operator understands his or her requirements, the FSDO will issue a Letter of Authorization (LOA). The operator may begin operations under an MEL authorization while developing the procedures document. If a procedure has not yet been developed for an item of equipment, then that item must be operative until the procedure is developed.

Once the procedures are in place for each item of equipment on the list, the operator must follow the appropriate procedure in the procedures document if an item of equipment becomes inoperative.