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Aircraft Maintenance


Maintenance is defined as the preservation, inspection, overhaul, and repair of an aircraft, including the replacement of parts. A PROPERLY MAINTAINED AIRCRAFT IS A SAFE AIRCRAFT. In addition, reg- ular and proper maintenance ensures that an aircraft meets an acceptable standard of airworthiness through- out its operational life.

Although maintenance requirements vary for different types of aircraft, experience shows that aircraft need some type of preventive maintenance every 25 hours of flying time or less, and minor maintenance at least every 100 hours. This is influenced by the kind of operation, climatic conditions, storage facilities, age, and construc- tion of the aircraft. Manufacturers supply maintenance manuals, parts catalogs, and other service information that should be used in maintaining the aircraft.


14 CFR part 91 places primary responsibility on the owner or operator for maintaining an aircraft in an airworthy condition. Certain inspections must be per- formed on the aircraft, and the owner must maintain the airworthiness of the aircraft during the time between required inspections by having any defects corrected.

14 CFR part 91, subpart E, requires the inspection of all civil aircraft at specific intervals to determine the overall condition. The interval depends upon the type of operations in which the aircraft is engaged. Some aircraft need to be inspected at least once each 12-calendar months, while inspection is required for others after each 100 hours of operation. In some instances, an aircraft may be inspected in accordance with an inspection system set up to provide for total inspection of the aircraft on the basis of calendar time, time in service, number of system operations, or any combination of these.

All inspections should follow the current manufac- turer’s maintenance manual, including the Instructions for Continued Airworthiness concerning inspections intervals, parts replacement, and life-limited items as applicable to the aircraft.


Any reciprocating-engine powered or single-engine- turbojet/turbo-propeller powered small aircraft (12,500 pounds and under) flown for business or pleasure and not flown for compensation or hire is required to be inspected at least annually. The inspection shall be performed by a certificated airframe and powerplant (A&P) mechanic who holds an Inspection Authorization (IA), by the manufacturer, or by a certificated and appro- priately rated repair station. The aircraft may not be operated unless the annual inspection has been performed within the preceding 12-calendar months. A period of 12-calendar months extends from any day of a month to the last day of the same month the following year. An aircraft overdue for an annual inspection may be operated under a Special Flight Permit issued by the FAA for the purpose of flying the aircraft to a location where the annual inspection can be performed. However, all applicable Airworthiness Directives that are due must be complied with.


All aircraft under 12,500 pounds (except turbojet/turbo- propeller powered multiengine airplanes and turbine powered rotorcraft), used to carry passengers for hire, must have received a 100-hour inspection within the preceding 100 hours of time in service and have been approved for return to service. Additionally, an aircraft used for flight instruction for hire, when provided by the person giving the flight instruction, must also have received a 100-hour inspection. This inspection must be performed by an FAA certificated A&P mechanic, an appropriately rated FAA certificated repair station, or by the aircraft manufacturer. An annual inspection, or an inspection for the issuance of an Airworthiness Certificate may be substituted for a required 100-hour inspection. The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done. The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service.


The annual and 100-hour inspection requirements do not apply to large (over 12,500 pounds) airplanes, turbojets, or turbo-propeller powered multiengine airplanes or to aircraft for which the owner complies with a progressive inspection program. Details of these requirements may be determined by reference to 14 CFR part 43, section 43.11 and part 91, subpart E, and by inquiring at a local FSDO.


14 CFR part 91, section 91.411 requires that the altime- ter, encoding altimeter, and related system be tested and inspected in the preceding 24 months before operated in controlled airspace under instrument flight rules (IFR).


14 CFR part 91, section 91.413 requires that before a transponder can be used under 14 CFR part 91, section 91.215(a), it shall be tested and inspected within the preceding 24 months.


The preflight inspection is a thorough and systematic means by which a pilot determines if the aircraft is air- worthy and in condition for safe operation. POHs and owner/information manuals contain a section devoted to a systematic method of performing a preflight inspection.


The Code of Federal Regulations (CFRs) requires that all aircraft instruments and installed equipment are operative prior to each departure. When the FAA adopted the minimum equipment list (MEL) con- cept for 14 CFR part 91 operations, this allowed for the first time, operations with inoperative items 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.

There are two primary methods of deferring main- tenance 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 part 91, section 91.213(d) and an FAA-approved MEL.

The deferral provision of 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 in-flight 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 mainte- nance that would ordinarily be required prior to flight.

Using the deferral provision of section 91.213(d), the pilot determines whether the inoperative equipment is required by type design, the CFRs, 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.

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 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. 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 part 91 are eligible to use the maintenance deferral provi- sions of 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 use of an MEL for an aircraft operated under 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, pream- ble, 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 supple- mental 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 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 con- ditions 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 Advisory Circular (AC) 91-67, Minimum Equipment Requirements for General Aviation Operations Under FAR Part 91.


Preventive maintenance is considered to be simple or minor preservation operations and the replacement of small standard parts, not involving complex assembly operations. Certificated pilots, excluding student pilots, sport pilots, and recreational pilots, may perform preventive maintenance on any aircraft that is owned or operated by them provided that aircraft is not used in air carrier service. (Sport pilots operating light sport aircraft, refer to 14 CFR part 65 for maintenance privileges.) 14 CFR part 43, Appendix A, contains a list of the operations that are considered to be preventive maintenance.


Repairs and alterations are classified as either major or minor. 14 CFR part 43, Appendix A, describes the alterations and repairs considered major. Major repairs or alterations shall be approved for return to service on FAA Form 337, Major Repairs and Major Alterations, by an appropriately rated certificated repair station, an FAA certificated A&P mechanic holding an Inspection Authorization, or a representative of the Administrator. Minor repairs and minor alterations may be approved for return to service with a proper entry in the maintenance records by an FAAcertificated A&Pmechanic or an appropriately certificated repair station.

For modifications of experimental aircraft, refer to the operating limitations issued to that aircraft. Modifications in accordance with FAA Order 8130.2, Airworthiness Certification of Aircraft and Related Products, may require the notification of the issuing authority.


A special flight permit is a Special Airworthiness Certificate issued authorizing operation of an aircraft that does not currently meet applicable airworthiness requirements but is safe for a specific flight. Before the permit is issued, an FAA inspector may personally inspect the aircraft, or require it to be inspected by an FAA certificated A&P mechanic or an appropriately certificated repair station, to determine its safety for the intended flight. The inspection shall be recorded in the aircraft records.

The special flight permit is issued to allow the aircraft to be flown to a base where repairs, alterations, or maintenance can be performed; for delivering or exporting the aircraft; or for evacuating an aircraft from an area of impending danger. A special flight permit may be issued to allow the operation of an overweight aircraft for flight beyond its normal range over water or land areas where adequate landing facilities or fuel is not available.

If a special flight permit is needed, assistance and the necessary forms may be obtained from the local FSDO or Designated Airworthiness Representative (DAR).

Airplain Ground schools Special Airworthiness Certificates Sample

[Figure 7-9 FAA Form 8130-7, Special Airworthiness Certificate.]


A primary safety function of the FAA is to require correction of unsafe conditions found in an aircraft, aircraft engine, propeller, or appliance when such conditions exist and are likely to exist or develop in other products of the same design. The unsafe condition may exist because of a design defect, maintenance, or other causes. 14 CFR part 39, Airworthiness Directives (ADs), defines the authority and responsibility of the Administrator for requiring the necessary corrective action. ADs are the means used to notify aircraft owners and other interested persons of unsafe conditions and to specify the conditions under which the product may continue to be operated.

ADs may be divided into two categories:

1. those of an emergency nature requiring immediate compliance prior to further flight, and

2. those of a less urgent nature requiring compliance within a specified period of time.

Airworthiness Directives are regulatory and shall be complied with unless a specific exemption is granted. It is the aircraft owner or operator’s responsibility to ensure compliance with all pertinent ADs. This includes those ADs that require recurrent or continuing action. For example, an AD may require a repetitive inspection each 50 hours of operation, meaning the particular inspection shall be accomplished and recorded every 50 hours of time in service. Owners/operators are reminded there is no provision to overfly the maximum hour requirement of an AD unless it is specifically written into the AD. To help determine if an AD applies to an amateur-built aircraft, contact the local FSDO.

14 CFR part 91, section 91.417 requires a record to be maintained that shows the current status of applicable ADs, including the method of compliance; the AD number and revision date, if recurring; the time and date when due again; the signature; kind of certificate; and certificate number of the repair station or mechanic who performed the work. For ready reference, many aircraft owners have a chronological listing of the per- tinent ADs in the back of their aircraft, engine, and propeller maintenance records.

All Airworthiness Directives and the AD Biweekly are free on the Internet at

Paper copies of the Summary of Airworthiness Directives and the AD Biweekly may be purchased from the Superintendent of Documents. The Summary contains all the valid ADs previously published and is divided into two areas. The small aircraft and rotorcraft books contain all ADs applicable to small aircraft (12,500 pounds or less maximum certificated takeoff weight) and ADs applicable to all helicopters. The large aircraft books contain all ADs applicable to large aircraft.

For further information on how to order ADs and the current price, contact:

U.S. Department of Transportation

Federal Aviation Administration

Delegation & Airworthiness Programs Branch,

AIR-140 P.O. Box 26460

Oklahoma City, OK 73125

Telephone Number: (405) 954-4103

Fax: (405) 954-4104


The registered owner/operator of an aircraft is responsible for certain items such as:

•Having a current Airworthiness Certificate and a Certificate of Aircraft Registration in the aircraft.

• Maintaining the aircraft in an airworthy condition, including compliance with all applicable Airworthiness Directives.

• Assuring that maintenance is properly recorded.

• Keeping abreast of current regulations concern- ing the operation and maintenance of the aircraft.

• Notifying the FAA Civil Aviation Registry immediately of any change of permanent mailing address, or of the sale or export of the aircraft, or of the loss of the eligibility to register an aircraft. (Refer to 14 CFR part 47, section 47.41.)

• Having a current FCC radio station license if equipped with radios, including emergency locator transmitter (ELT), if operated outside of the United States.

(Courtesy FAA)

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