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Pilot's Handbook of Aeronautical Knowledge
Flight Manuals and Other Documents

Minimum Equipment Lists (MEL) and
Operations With Inoperative Equipment

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Minimum Equipment Lists (MEL) and
Operations With Inoperative Equipment

14 CFR requires that all aircraft instruments and installed
equipment be operative prior to each departure. When the
FAA adopted the minimum equipment list (MEL) concept
for 14 CFR part 91 operations, this allowed operations with
inoperative equipment determined to be nonessential for safe
flight. At the same time, it allowed part 91 operators, without
an MEL, to defer repairs on nonessential equipment within
the guidelines of part 91.

The FAA has two acceptable methods of deferring
maintenance on small rotorcraft, non-turbine powered
airplanes, gliders, or lighter-than-air aircraft operated under
part 91. They are the deferral provision of 14 CFR section
91.213(d) and an FAA-approved MEL.

The deferral provision of 14 CFR section 91.213(d) is
widely used by most pilot/operators. Its popularity is due
to simplicity and minimal paperwork. When inoperative
equipment is found during preflight or prior to departure, the
decision should be to cancel the flight, obtain maintenance
prior to flight, or to defer the item or equipment. Maintenance deferrals are not used for inflight discrepancies.

The manufacturer's AFM/POH procedures are to be used in
those situations. The discussion that follows assumes that
the pilot wishes to defer maintenance that would ordinarily
be required prior to flight.

Using the deferral provision of 14 CFR section 91.213(d),
the pilot determines whether the inoperative equipment is
required by type design, 14 CFR, or ADs. If the inoperative
item is not required, and the aircraft can be safely operated
without it, the deferral may be made. The inoperative item
shall be deactivated or removed and an INOPERATIVE
placard placed near the appropriate switch, control, or
indicator. If deactivation or removal involves maintenance
(removal always will), it must be accomplished by certificated
maintenance personnel and recorded in accordance with 14
CFR part 43.

For example, if the position lights (installed equipment)
were discovered to be inoperative prior to a daytime flight,
the pilot would follow the requirements of 14 CFR section

The deactivation may be a process as simple as the pilot
positioning a circuit breaker to the OFF position, or as
complex as rendering instruments or equipment totally
inoperable. Complex maintenance tasks require a certificated
and appropriately rated maintenance person to perform the
deactivation. In all cases, the item or equipment must be
placarded INOPERATIVE.

All small rotorcraft, non-turbine powered airplanes, gliders,
or lighter-than-air aircraft operated under 14 CFR part 91
are eligible to use the maintenance deferral provisions of 14
CFR section 91.213(d). However, once an operator requests
an MEL, and a Letter of Authorization (LOA) is issued by the
FAA, then the use of the MEL becomes mandatory for that
aircraft. All maintenance deferrals must be accomplished in
accordance with the terms and conditions of the MEL and
the operator-generated procedures document.

The FAA has developed master minimum equipment lists
(MMELs) for aircraft in current use. Upon written request by
an operator, the local FSDO may issue the appropriate make
and model MMEL, along with an LOA, and the preamble.
The operator then develops operations and maintenance
(O&M) procedures from the MMEL. This MMEL with O&M
procedures now becomes the operator's MEL. The MEL,
LOA, preamble, and procedures document developed by the
operator must be on board the aircraft when it is operated.
The FAA considers an approved MEL to be a supplemental
type certificate (STC) issued to an aircraft by serial number
and registration number. It, therefore, becomes the authority
to operate that aircraft in a condition other than originally
type certificated.

With an approved MEL, if the position lights were discovered
inoperative prior to a daytime flight, the pilot would make
an entry in the maintenance record or discrepancy record
provided for that purpose. The item is then either repaired or
deferred in accordance with the MEL. Upon confirming that
daytime flight with inoperative position lights is acceptable in
accordance with the provisions of the MEL, the pilot would
leave the position lights switch OFF, open the circuit breaker
(or whatever action is called for in the procedures document),
and placard the position light switch as INOPERATIVE.

There are exceptions to the use of the MEL for deferral. For
example, should a component fail that is not listed in the MEL
as deferrable (the tachometer, flaps, or stall warning device,
for example), then repairs are required to be performed prior
to departure. If maintenance or parts are not readily available
at that location, a special flight permit can be obtained from
the nearest FSDO. This permit allows the aircraft to be
.own to another location for maintenance. This allows an
aircraft that may not currently meet applicable airworthiness
requirements, but is capable of safe flight, to be operated
under the restrictive special terms and conditions attached
to the special flight permit.

Deferral of maintenance is not to be taken lightly,
and due consideration should be given to the effect an
inoperative component may have on the operation of an
aircraft, particularly if other items are inoperative. Further
information regarding MELs and operations with inoperative
equipment can be found in AC 91-67, Minimum Equipment
Requirements for General Aviation Operations Under CFR
Part 91.