Minimum Equipment Lists (MELs) contain provisions for flight with inoperative equipment based on the conditions of that particular flight
Additionally, it provides for equipment repairs to be deferred until a later point in time
Determining if an aircraft is airworthy is dependent on the MEL, or FAR 91.213
Whether or not your airplane has an MEL, FAR 91.213 still applies to all inoperative equipment and it is your responsibility to find out if your airplane has an MEL
Minimum Equipment Lists (MEL) and Operations With Inoperative Equipment:
Minimum Equipment List
Under 14 CFR, all aircraft instruments and installed equipment are required to be operative prior to each departure
When the FAA adopted the minimum equipment list (MEL) concept for 14 CFR part 91 operations, it allowed aircraft to be operated 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:
The deferral provision of 14 CFR, part 91, section 91.213(d), and
An FAA-approved MEL
Deferral:
The deferral provision of 14 CFR, part 91, 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 a preflight inspection 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
Assuming the pilot wishes to defer maintenance for equipment that would ordinarily be required prior to flight:
The pilot first 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, part 91, section 91.213(d)
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
Minimum Equipment List:
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 use of an MEL for an aircraft operated under 14 CFR part 91 also allows for the deferral of inoperative items or equipment
The primary guidance becomes the FAA-approved MEL issued to that specific operator and N-numbered aircraft
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 during each operation
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 would then either be 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 flown 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
Minimum Equipment List
Minimum Equipment List Description:
There are two categories of procedures: maintenance procedures (M) and operations procedures (O)
An authorized mechanic must complete "M" procedures, but the pilot or flight crew can do "O" procedures
Once the owner/operator has created the procedures document, it is presented to the FAA for approval. If granted, the FAA inspector will issue a letter of authorization (LOA). When this letter is received the MEL is complete and the aircraft may be operated within the guidelines of the MEL rather than the procedures outlined in the regulations. This formula will help you remember: MMEL + Procedures Document + LOA = MEL
When a part of the aircraft is found to be inoperative the pilot will refer to the MEL
If the item is not in the procedures document, the aircraft is grounded
If the item is found, the pilot will take the appropriate actions required by the procedures document before flight
An MEL is equivalent to a supplemental type certificate and is required to be on board the aircraft during flight
The MEL is only valid for a specific aircraft and cannot be transferred to another
Column one shows each piece of equipment, listed by system [Figure 1]
Column two shows how many of that item are installed on the aircraft [Figure 1]
Column three shows the number of items installed that have to be operational for the aircraft to be airworthy [Figure 1]
Column four shows remarks or exceptions [Figure 1]
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 FAR Part 91
