Studying FAA regulations for the A&P certificate can feel overwhelming at first. There are a lot of regulation numbers, and many of them sound similar until you understand what each one is actually used for.

In class, these are often called FARs, meaning Federal Aviation Regulations. Technically, they are found in Title 14 of the Code of Federal Regulations, usually written as 14 CFR. So when someone says FAR Part 43, they usually mean 14 CFR Part 43.

This post is written as a blog post and a study guide for A&P students. The goal is not to memorize every word of every regulation. The goal is to understand what each Part covers, why an Aviation Maintenance Technician should care, and which items are most likely to show up on the written, oral, or practical exam.

The FAR-AMT regulations covered here are:

  • Part 1
  • Part 21
  • Part 23
  • Part 25
  • Part 27
  • Part 29
  • Part 33
  • Part 35
  • Part 39
  • Part 43
  • Part 45
  • Part 47
  • Part 65
  • Part 91
  • Part 119
  • Part 121
  • Part 125
  • Part 135
  • Part 145
  • Part 147
  • Part 43 Appendix A
  • Part 43 Appendix B
  • Part 43 Appendix C
  • Part 43 Appendix D

Big Picture: How the FAR-AMTs Fit Together

A&P students should think of the regulations as a system.

Some Parts deal with definitions. Some deal with aircraft certification. Some deal with maintenance rules. Some deal with mechanic privileges. Some deal with aircraft operations. Some deal with repair stations and schools.

Here is the basic map:

Regulation Main Idea
Part 1 FAA definitions and abbreviations
Part 21 Certification of products and articles
Part 23 Normal category airplanes
Part 25 Transport category airplanes
Part 27 Normal category rotorcraft
Part 29 Transport category rotorcraft
Part 33 Aircraft engines
Part 35 Propellers
Part 39 Airworthiness Directives
Part 43 Maintenance, preventive maintenance, rebuilding, and alterations
Part 45 Identification and registration marking
Part 47 Aircraft registration
Part 65 Mechanic certification, ratings, privileges, and limitations
Part 91 General operating and flight rules
Part 119 Certification of air carriers and commercial operators
Part 121 Domestic, flag, and supplemental air carrier operations
Part 125 Certain large-aircraft operations
Part 135 Commuter and on-demand operations
Part 145 Repair stations
Part 147 Aviation Maintenance Technician Schools

A good memory aid is:

Part 43 tells you how maintenance is performed and recorded. Part 65 tells you who the mechanic is and what the mechanic can do. Part 91 tells you who is responsible for keeping the aircraft airworthy.

Part 1 — Definitions and Abbreviations

Part 1 contains definitions and abbreviations used throughout the FAA regulations.

This Part matters because FAA terms often have specific regulatory meanings. A word may sound simple in everyday language, but in the CFR it may have a precise definition.

Examples of important terms include:

  • Aircraft
  • Airframe
  • Aircraft engine
  • Appliance
  • Approved
  • Category
  • Class
  • Large aircraft
  • Maintenance
  • Preventive maintenance
  • Propeller
  • Rating
  • Small aircraft
  • Time in service

Why Part 1 Matters to A&P Students

A&P students should not skip Part 1. Many test questions depend on knowing what a term means under the regulations.

For example, the word maintenance does not just mean “working on an aircraft.” Under FAA usage, maintenance includes inspection, overhaul, repair, preservation, and replacement of parts, but preventive maintenance is treated separately.

That matters because different rules apply to maintenance, preventive maintenance, alterations, inspections, and rebuilding.

Study Points

Remember:

  • Part 1 defines important FAA terms.
  • Regulatory definitions may be different from everyday language.
  • Definitions affect how other regulations are interpreted.
  • When in doubt, look up the definition first.

Part 21 — Certification Procedures for Products and Articles

Part 21 covers certification procedures for products and articles.

In FAA language, products generally include:

  • Aircraft
  • Aircraft engines
  • Propellers

Articles can include parts, components, materials, appliances, and other items used in aviation.

Part 21 explains how aircraft, engines, propellers, and articles are approved by the FAA.

Important Part 21 Concepts

A&P students should know these terms:

  • Type Certificate
  • Type Certificate Data Sheet
  • Supplemental Type Certificate
  • Production Certificate
  • Parts Manufacturer Approval
  • Technical Standard Order authorization
  • Airworthiness certificate

Type Certificate

A Type Certificate, or TC, is FAA approval of the design of an aircraft, aircraft engine, or propeller.

A TC means the FAA has approved the product’s design as meeting the applicable airworthiness standards.

For a mechanic, the important idea is this:

An aircraft must conform to its approved type design and be in a condition for safe operation.

Type Certificate Data Sheet

A Type Certificate Data Sheet, or TCDS, contains important information about the approved design.

A TCDS may include:

  • Approved models
  • Engine eligibility
  • Propeller eligibility
  • Fuel requirements
  • Oil requirements
  • Operating limitations
  • Required placards
  • Weight and balance limits
  • Certification basis

A&P students should understand that the TCDS is not just paperwork. It helps determine whether an aircraft is properly configured.

Supplemental Type Certificate

A Supplemental Type Certificate, or STC, approves a major change to a type-certificated product.

Simple memory aid:

TC = original approved design. STC = approved major change to that design.

Examples of STC-related changes may include:

  • Engine conversions
  • Major avionics installations
  • Fuel system modifications
  • Structural modifications
  • Performance modifications

Parts Manufacturer Approval

Parts Manufacturer Approval, or PMA, is FAA approval to produce replacement or modification parts.

A PMA part is an approved part, but the mechanic still has to determine whether it is eligible for installation on the specific aircraft, engine, propeller, or appliance.

Important study point:

Approved part does not automatically mean approved installation.

Technical Standard Order

A Technical Standard Order, or TSO, is a minimum performance standard for certain articles.

A TSO authorization means the article meets the applicable TSO standard. It does not automatically approve installation on a specific aircraft.

For example, a TSO-authorized radio may still need an approved installation for a particular aircraft.

Study Points

Remember:

  • Part 21 is about certification of products and articles.
  • A Type Certificate approves the original design.
  • A TCDS gives important approved configuration information.
  • An STC approves a major change to a type-certificated product.
  • A PMA approves production of replacement or modification parts.
  • A TSO means the article meets a standard, but installation still has to be approved.

Part 23 — Airworthiness Standards: Normal Category Airplanes

Part 23 contains airworthiness standards for normal category airplanes.

Many general aviation airplanes are associated with Part 23 certification standards.

This includes many smaller aircraft used for:

  • Training
  • Personal flying
  • Business flying
  • General aviation operations

Why Part 23 Matters to Mechanics

A&P students do not usually memorize Part 23 in detail, but they should know what it is.

Part 23 is a design and certification standard. It helps define what normal category airplanes must meet to receive type certification.

Part 23 can involve standards for:

  • Structures
  • Flight characteristics
  • Performance
  • Powerplant installation
  • Systems and equipment
  • Occupant protection

Study Points

Remember:

  • Part 23 applies to normal category airplanes.
  • It is mainly a design and certification standard.
  • Many small general aviation airplanes are connected to Part 23.
  • Mechanics may encounter Part 23 indirectly through approved data, aircraft limitations, and certification documents.

Part 25 — Airworthiness Standards: Transport Category Airplanes

Part 25 contains airworthiness standards for transport category airplanes.

Transport category airplanes are generally larger and more complex than normal category airplanes. Airline-type aircraft are commonly associated with Part 25 certification standards.

Why Part 25 Matters to Mechanics

Part 25 aircraft often have complex systems such as:

  • Turbine engines
  • Pressurization
  • Fire protection systems
  • Hydraulic systems
  • Redundant electrical systems
  • Advanced flight controls
  • Transport-category structural requirements

Mechanics working on airline or large commercial aircraft may deal with Part 25 aircraft frequently.

Study Points

Remember:

  • Part 25 applies to transport category airplanes.
  • It is mainly a design and certification standard.
  • Airline-type airplanes are commonly associated with Part 25.
  • Part 23 and Part 25 are both airplane standards, but they apply to different categories.

Memory aid:

Part 23 = normal category airplanes. Part 25 = transport category airplanes.

Part 27 — Airworthiness Standards: Normal Category Rotorcraft

Part 27 contains airworthiness standards for normal category rotorcraft.

Rotorcraft include helicopters and other aircraft that depend mainly on rotating airfoils for lift.

Why Part 27 Matters to Mechanics

Rotorcraft have unique systems that are different from fixed-wing airplanes.

Examples include:

  • Main rotor systems
  • Tail rotor systems
  • Transmission systems
  • Rotor blades
  • Dynamic components
  • Rotor flight controls
  • Drive systems

Mechanics working on helicopters must understand that rotorcraft are certificated under different standards from airplanes.

Study Points

Remember:

  • Part 27 applies to normal category rotorcraft.
  • It is mainly a design and certification standard.
  • Rotorcraft have unique structures, controls, and dynamic components.
  • Helicopter maintenance often involves life-limited parts and critical inspections.

Part 29 — Airworthiness Standards: Transport Category Rotorcraft

Part 29 contains airworthiness standards for transport category rotorcraft.

These are larger or more complex rotorcraft than normal category rotorcraft.

Why Part 29 Matters to Mechanics

Part 29 rotorcraft may be used in operations such as:

  • Offshore transport
  • Emergency medical services
  • Heavy-lift operations
  • Commercial transport
  • Corporate transport

These aircraft may have more complex requirements for:

  • Performance
  • Structures
  • Occupant safety
  • Systems
  • Powerplant installation
  • Fire protection
  • Continued airworthiness

Study Points

Remember:

  • Part 29 applies to transport category rotorcraft.
  • Part 27 applies to normal category rotorcraft.
  • Rotorcraft standards are separate from airplane standards.
  • Larger helicopters are commonly associated with Part 29.

Memory aid:

Part 27 = normal category rotorcraft. Part 29 = transport category rotorcraft.

Part 33 — Airworthiness Standards: Aircraft Engines

Part 33 contains airworthiness standards for aircraft engines.

This is a certification standard, not a mechanic licensing regulation.

Why Part 33 Matters to Mechanics

Mechanics work on engines every day, but Part 33 is about how engines are certificated.

Part 33 deals with standards related to:

  • Engine design
  • Engine operation
  • Endurance
  • Engine ratings
  • Engine limitations
  • Safety
  • Engine components

Mechanics usually interact with Part 33 indirectly through:

  • Engine Type Certificate Data Sheets
  • Engine maintenance manuals
  • Engine limitations
  • Airworthiness Directives
  • Service information
  • Approved repair procedures

Study Points

Remember:

  • Part 33 applies to aircraft engine airworthiness standards.
  • It is a design and certification regulation.
  • Mechanics maintain engines according to approved or acceptable data.
  • Engine certification and engine maintenance are related, but they are not the same thing.

Part 35 — Airworthiness Standards: Propellers

Part 35 contains airworthiness standards for propellers.

Like Part 33, this is a certification standard.

Why Part 35 Matters to Mechanics

Propellers are certificated products. They are not just accessories bolted to an engine.

Propeller maintenance can involve:

  • Blade condition
  • Nicks
  • Cracks
  • Corrosion
  • Balance
  • Hub condition
  • Pitch change mechanisms
  • Anti-icing systems
  • Governor operation
  • Overhaul requirements

Improper propeller maintenance can create serious vibration, structural, and safety problems.

Study Points

Remember:

  • Part 35 applies to propeller airworthiness standards.
  • Propellers may have their own Type Certificate Data Sheets.
  • Propeller damage and repair limits must be taken seriously.
  • Propeller maintenance must follow approved or acceptable data.

Part 39 — Airworthiness Directives

Part 39 covers Airworthiness Directives, commonly called ADs.

This is one of the most important regulations for A&P students.

An Airworthiness Directive is a legally enforceable FAA rule issued to correct an unsafe condition in an aircraft, aircraft engine, propeller, or appliance.

The key point is simple:

Airworthiness Directives are mandatory.

Why ADs Exist

The FAA issues an AD when it finds that:

  1. An unsafe condition exists, and
  2. That condition is likely to exist or develop in other products of the same type design.

ADs may be issued because of:

  • Accidents
  • Service difficulty reports
  • Manufacturer reports
  • Inspections
  • Operational experience
  • Design problems
  • Manufacturing problems

What an AD May Require

An AD may require:

  • Inspection
  • Repetitive inspection
  • Repair
  • Replacement
  • Modification
  • Operating limitation
  • Procedure change
  • Removal of a part from service

Some ADs are one-time actions. Others are recurring.

ADs vs. Service Bulletins

Students often confuse ADs and Service Bulletins.

A Service Bulletin is issued by a manufacturer. It may contain important instructions or recommendations, but it is not automatically mandatory for every aircraft.

An AD is mandatory because it is an FAA rule.

Memory aid:

AD = mandatory. Service Bulletin = not automatically mandatory.

However, an AD may reference a Service Bulletin as the method of compliance. In that case, the Service Bulletin becomes part of the required compliance method.

AD Recordkeeping

Good AD records should show:

  • AD number
  • Applicability
  • Method of compliance
  • Date of compliance
  • Aircraft or component time
  • Whether the AD is recurring
  • Next due date or time, if recurring

Study Points

Remember:

  • Part 39 covers Airworthiness Directives.
  • ADs are legally enforceable.
  • ADs are mandatory.
  • AD compliance is part of airworthiness.
  • Service Bulletins are not automatically mandatory unless made mandatory by an AD, regulation, or operating rule.

Part 43 — Maintenance, Preventive Maintenance, Rebuilding, and Alteration

Part 43 is one of the most important regulations for A&P students.

Part 43 explains how maintenance, preventive maintenance, rebuilding, and alterations must be performed and recorded.

Why Part 43 Matters

Part 43 answers major maintenance questions:

  • Who may perform maintenance?
  • Who may approve work for return to service?
  • What performance standards apply?
  • What records are required?
  • What makes a repair or alteration major?
  • What inspections require specific checklist items?

Important Part 43 Sections

A&P students should know these sections especially well:

Section Main Idea
§43.3 Persons authorized to perform maintenance
§43.5 Approval for return to service after maintenance
§43.7 Persons authorized to approve for return to service
§43.9 Maintenance record entries
§43.11 Inspection record entries
§43.13 Performance rules
§43.15 Additional performance rules for inspections
§43.16 Airworthiness limitations

§43.3 — Persons Authorized to Perform Maintenance

Section 43.3 explains who may perform maintenance, preventive maintenance, rebuilding, and alterations.

Depending on the situation, this may include:

  • Certificated mechanics
  • Repairmen
  • Repair stations
  • Air carriers
  • Manufacturers
  • Certain pilots performing preventive maintenance
  • Persons working under supervision

The important point is that not everyone may legally perform aircraft maintenance.

§43.7 — Persons Authorized to Approve for Return to Service

Section 43.7 explains who may approve an aircraft, airframe, aircraft engine, propeller, appliance, or component part for return to service after maintenance, preventive maintenance, rebuilding, or alteration.

This matters because performing the work and approving the work are not always the same thing.

Return to service is a legal approval.

§43.9 — Maintenance Record Entries

Section 43.9 covers maintenance record entries.

A normal maintenance entry generally includes:

  • Description of work performed
  • Date of completion
  • Name of the person who performed the work
  • Signature, certificate number, and kind of certificate held by the person approving the work

Memory aid:

What was done, when it was done, who did it, and who approved it.

§43.11 — Inspection Record Entries

Section 43.11 covers inspection record entries.

Inspection entries are different from normal maintenance entries because they document the performance and result of an inspection.

Inspection entries commonly include:

  • Type of inspection
  • Brief description of the extent of the inspection
  • Date of inspection
  • Aircraft total time in service
  • Signature and certificate information
  • Statement of airworthy condition, or a statement that discrepancies were provided

§43.13 — Performance Rules

Section 43.13 explains general performance rules.

Maintenance must be performed using methods, techniques, and practices acceptable to the Administrator. The mechanic must use the tools, equipment, and test apparatus necessary to assure the work is completed properly.

Simple memory aid:

Use proper data, proper tools, and proper workmanship.

Study Points

Remember:

  • Part 43 is a core A&P regulation.
  • It governs maintenance performance and records.
  • §43.9 is for maintenance entries.
  • §43.11 is for inspection entries.
  • §43.13 is about acceptable methods, techniques, practices, tools, and workmanship.

Part 43 Appendix A — Major Alterations, Major Repairs, and Preventive Maintenance

Part 43 Appendix A is one of the most testable areas for A&P students.

It helps identify:

  • Major alterations
  • Major repairs
  • Preventive maintenance

This classification matters because it affects:

  • Who may perform the work
  • Who may approve the work
  • What data is required
  • What record entry is required
  • Whether FAA Form 337 may be required

Major Alterations

A major alteration is an alteration that may appreciably affect airworthiness factors such as:

  • Weight
  • Balance
  • Structural strength
  • Performance
  • Powerplant operation
  • Flight characteristics
  • Other qualities affecting airworthiness

Major does not necessarily mean physically large.

A small alteration can be major if it affects airworthiness.

Major Repairs

A major repair is a repair that, if improperly done, might appreciably affect airworthiness.

Examples may involve important structures or systems such as:

  • Wings
  • Fuselage
  • Control systems
  • Landing gear
  • Engine mounts
  • Spars
  • Structural members
  • Propeller repairs

Preventive Maintenance

Preventive maintenance is limited maintenance specifically listed in Appendix A.

Preventive maintenance does not simply mean “easy maintenance.” It is a defined regulatory category.

Examples commonly associated with preventive maintenance include simple servicing or replacement tasks that do not involve complex assembly operations.

Study Points

Remember:

  • Appendix A covers major alterations, major repairs, and preventive maintenance.
  • Major means the work may appreciably affect airworthiness.
  • Preventive maintenance is specifically listed; it is not just any simple task.
  • Classification affects approval, documentation, and return to service.

Memory aid:

Major does not mean big. Major means it may affect airworthiness.

Part 43 Appendix B — Recording of Major Repairs and Major Alterations

Part 43 Appendix B covers recording major repairs and major alterations.

This Appendix is important because major repairs and major alterations often require additional documentation beyond a simple logbook entry.

FAA Form 337

A major repair or major alteration is commonly recorded on FAA Form 337, Major Repair and Alteration.

This form documents important information about the aircraft, the work performed, the approval basis, and the return-to-service approval.

Why Appendix B Matters

A&P students should understand that major repairs and major alterations are treated differently from minor work.

Appendix B explains how these major repairs and alterations are recorded and how the required form is handled.

Study Points

Remember:

  • Appendix B covers recording major repairs and major alterations.
  • FAA Form 337 is commonly associated with major repairs and major alterations.
  • Major work requires proper documentation.
  • The paperwork is part of the airworthiness record.

Part 43 Appendix C — Reserved

Part 43 Appendix C is reserved.

That means there is currently no active regulatory content in Appendix C.

Why Study a Reserved Appendix?

A&P students should still recognize Appendix C because it appears in the structure of Part 43.

If a quiz asks what Appendix C contains, the answer is:

Appendix C is reserved.

Study Points

Remember:

  • Appendix C is reserved.
  • It does not currently contain active requirements.
  • Do not confuse Appendix C with Appendix D, E, or F.

Part 43 Appendix D — Annual and 100-Hour Inspection Scope and Detail

Part 43 Appendix D covers the scope and detail of items to be included in annual and 100-hour inspections.

This is a very important inspection regulation.

Appendix D tells the person performing the inspection what areas must be inspected, where applicable.

What Appendix D Covers

Appendix D includes inspection areas such as:

  • Fuselage and hull group
  • Cabin and cockpit group
  • Engine and nacelle group
  • Landing gear group
  • Wing and center section group
  • Empennage group
  • Propeller group
  • Radio group
  • Miscellaneous items

Why Appendix D Matters

Annual and 100-hour inspections are not casual walkarounds. They have a required scope and level of detail.

The mechanic or IA performing the inspection must use a checklist. That checklist must include the scope and detail of Appendix D.

Annual vs. 100-Hour Inspection

Annual inspection:

  • Required every 12 calendar months for many aircraft
  • Must be performed by an IA or other authorized person

100-hour inspection:

  • Required for certain aircraft operations, such as carrying passengers for hire or flight instruction for hire
  • May be performed by an appropriately rated A&P mechanic
  • May be exceeded by not more than 10 hours while en route to a place where the inspection can be performed
  • The excess time counts toward the next 100 hours

Study Points

Remember:

  • Appendix D covers what must be inspected during annual and 100-hour inspections.
  • The inspection must use a checklist.
  • The checklist must include Appendix D scope and detail.
  • Annual inspections and 100-hour inspections are similar in scope, but not identical in who may perform them.

Part 45 — Identification and Registration Marking

Part 45 covers identification and registration marking.

This Part includes rules for marking aircraft, engines, propellers, and certain parts.

Why Part 45 Matters to Mechanics

Mechanics need to understand that aircraft and major products must be properly identified.

Identification plates and markings help establish:

  • Aircraft identity
  • Engine identity
  • Propeller identity
  • Manufacturer information
  • Model information
  • Serial number information
  • Registration markings

Aircraft N-Numbers

Part 45 also deals with registration markings, commonly called N-numbers on U.S.-registered aircraft.

These markings identify the aircraft and connect it to its registration.

Study Points

Remember:

  • Part 45 covers identification and registration marking.
  • Aircraft, engines, and propellers have identification requirements.
  • N-numbers are aircraft registration markings.
  • Identification plates and markings matter for traceability and airworthiness records.

Part 47 — Aircraft Registration

Part 47 covers aircraft registration.

This Part explains how aircraft are registered in the United States.

Why Part 47 Matters to Mechanics

A&P mechanics usually do not handle aircraft registration as their main job, but registration status still matters.

An aircraft must be properly registered to operate legally, unless an exception applies.

Registration records connect the aircraft to:

  • Owner information
  • N-number
  • Aircraft identity
  • FAA aircraft records

Registration vs. Airworthiness

A&P students should understand that registration and airworthiness are different.

An aircraft can be registered but not airworthy.

An aircraft can be physically capable of flight but not legally operable if registration or airworthiness requirements are not met.

Study Points

Remember:

  • Part 47 covers aircraft registration.
  • Registration identifies the aircraft and owner.
  • Registration is not the same thing as airworthiness.
  • Part 45 covers markings; Part 47 covers registration.

Memory aid:

Part 45 = markings. Part 47 = registration.

Part 65 — Certification: Airmen Other Than Flight Crewmembers

Part 65 is one of the most important Parts for A&P students.

Part 65 covers certification for airmen other than flight crewmembers. For mechanics, the important section is Subpart D, which covers mechanic certification.

Important Mechanic Sections

A&P students should know:

Section Main Idea
§65.71 Eligibility requirements
§65.73 Ratings
§65.75 Knowledge requirements
§65.77 Experience requirements
§65.79 Skill requirements
§65.81 General privileges and limitations
§65.83 Recent experience requirements
§65.85 Airframe rating privileges
§65.87 Powerplant rating privileges
§65.89-§65.95 Inspection Authorization

§65.71 — Eligibility Requirements

Section 65.71 covers basic eligibility for a mechanic certificate.

In general, a mechanic applicant must:

  • Be at least 18 years old
  • Be able to read, write, speak, and understand English
  • Meet knowledge, experience, and skill requirements

§65.73 — Ratings

Section 65.73 identifies the two mechanic ratings:

  • Airframe
  • Powerplant

A mechanic may hold one or both ratings.

A person who holds both ratings is commonly called an A&P mechanic.

§65.81 — General Privileges and Limitations

Section 65.81 explains what a certificated mechanic may do.

A mechanic may perform or supervise maintenance, preventive maintenance, or alteration of an aircraft or appliance, or part thereof, for which the mechanic is rated.

The phrase for which the mechanic is rated is very important.

A mechanic certificate is not unlimited authority.

A mechanic must also understand current manufacturer instructions and maintenance manuals for the specific operation concerned.

§65.83 — Recent Experience

Section 65.83 requires recent experience before a mechanic may exercise certificate privileges.

A mechanic certificate does not simply expire every 24 months, but the mechanic must meet recent experience requirements to exercise privileges.

Inspection Authorization

Inspection Authorization, or IA, is an additional authorization held by some experienced A&P mechanics.

An IA may perform certain inspections and approvals, such as annual inspections and approval for return to service after certain major repairs or major alterations.

Study Points

Remember:

  • Part 65 covers mechanic certification.
  • Airframe and Powerplant are separate ratings.
  • A&P means the mechanic holds both ratings.
  • §65.81 covers privileges and limitations.
  • A mechanic must work within rating, data, and regulatory limits.
  • IA is not the same thing as A&P.

Part 91 — General Operating and Flight Rules

Part 91 contains general operating and flight rules.

Even though Part 91 is often thought of as a pilot/operator regulation, it is extremely important for mechanics.

Part 91 includes major maintenance responsibility, inspection, and recordkeeping requirements.

Important Part 91 Maintenance Sections

A&P students should know:

Section Main Idea
§91.403 General maintenance responsibility
§91.405 Maintenance required
§91.407 Operation after maintenance
§91.409 Inspections
§91.411 Altimeter/static system checks
§91.413 Transponder checks
§91.417 Maintenance records

§91.403 — General

Section 91.403 states that the owner or operator is primarily responsible for maintaining the aircraft in an airworthy condition, including compliance with Airworthiness Directives.

This is a major test point.

§91.405 — Maintenance Required

Section 91.405 explains what the owner or operator must ensure, including required inspections, correction of discrepancies, and proper maintenance record entries.

§91.407 — Operation After Maintenance

Section 91.407 says an aircraft may not be operated after maintenance, preventive maintenance, rebuilding, or alteration unless it has been approved for return to service by an authorized person and the required maintenance record entry has been made.

§91.409 — Inspections

Section 91.409 covers required inspections, including annual inspections and 100-hour inspections.

Annual inspection:

  • Every 12 calendar months
  • Usually requires an IA

100-hour inspection:

  • Required for certain operations
  • May be performed by an appropriately rated A&P mechanic
  • May be exceeded by not more than 10 hours only to reach a place where the inspection can be done
  • Excess time counts toward the next 100 hours

§91.411 — Altimeter System and Altitude Reporting Equipment Tests

Section 91.411 covers altimeter system and altitude reporting equipment tests and inspections.

This is commonly remembered as a 24-calendar-month requirement for applicable operations.

§91.413 — ATC Transponder Tests and Inspections

Section 91.413 covers ATC transponder tests and inspections.

This is also commonly remembered as a 24-calendar-month requirement.

Memory aid:

§91.411 = altimeter/static/altitude reporting. §91.413 = transponder.

§91.417 — Maintenance Records

Section 91.417 covers maintenance records.

Important records include:

  • Maintenance records
  • Inspection records
  • Current status of life-limited parts
  • Time since last overhaul, if required
  • Current inspection status
  • Current status of applicable ADs
  • Major alteration records

Study Points

Remember:

  • Part 91 places primary airworthiness responsibility on the owner/operator.
  • §91.407 connects operation after maintenance to Part 43 return-to-service records.
  • §91.409 covers annual and 100-hour inspections.
  • §91.411 and §91.413 are commonly 24-calendar-month checks.
  • §91.417 covers maintenance records.

Part 119 — Certification: Air Carriers and Commercial Operators

Part 119 covers certification requirements for air carriers and commercial operators.

This Part helps determine what kind of operating certificate is required for certain commercial operations.

Why Part 119 Matters to A&P Students

Part 119 matters because it helps connect operators to Parts 121 and 135.

In simple terms, Part 119 helps answer:

  • Does this operator need an air carrier certificate?
  • Does this operator need a commercial operator certificate?
  • What operating rules apply?
  • Is the operation conducted under Part 121 or Part 135?

Study Points

Remember:

  • Part 119 is about certification of air carriers and commercial operators.
  • It helps determine whether Part 121 or Part 135 applies.
  • Mechanics may encounter Part 119 indirectly when working for commercial operators.
  • The operating rules affect maintenance requirements and maintenance programs.

Part 121 — Operating Requirements: Domestic, Flag, and Supplemental Operations

Part 121 covers operating requirements for domestic, flag, and supplemental operations.

This is the Part commonly associated with airlines and large air carrier operations.

Why Part 121 Matters to Mechanics

Part 121 operators have extensive maintenance requirements and approved maintenance programs.

Mechanics working for airlines may work under a Part 121 maintenance program instead of simply performing work under basic general aviation Part 91 maintenance practices.

Part 121 operations may involve:

  • Continuous airworthiness maintenance programs
  • Required inspection programs
  • Maintenance manuals
  • Maintenance control
  • Required records
  • Air carrier procedures
  • Approved maintenance organizations
  • Large transport category aircraft

Study Points

Remember:

  • Part 121 is commonly associated with airline operations.
  • Part 121 operators have approved maintenance programs.
  • Mechanics must follow the carrier’s manuals and procedures.
  • Part 121 maintenance is more structured than typical small-aircraft Part 91 maintenance.

Part 125 — Certification and Operations: Certain Large Aircraft

Part 125 applies to certain operations of large aircraft that are not necessarily operated as common-carrier airline operations.

This Part can be confusing because students often hear Part 121 and Part 135 more often.

Why Part 125 Matters to A&P Students

Part 125 is important because not every large aircraft operation is an airline, and not every large aircraft operation is Part 121.

Part 125 may apply to certain large aircraft operations when the operation does not fall under Part 121, 129, 135, or other specific rules.

Study Points

Remember:

  • Part 125 applies to certain large aircraft operations.
  • It is not the same as Part 121.
  • It is not the same as Part 135.
  • It fills a regulatory space for certain large aircraft operations.

Memory aid:

Part 121 = airline-type air carrier operations. Part 135 = commuter/on-demand operations. Part 125 = certain large-aircraft operations that are not necessarily Part 121 or Part 135.

Part 135 — Operating Requirements: Commuter and On-Demand Operations

Part 135 covers commuter and on-demand operations.

This Part is commonly associated with:

  • Charter operations
  • Air taxi operations
  • Some commuter operations
  • On-demand cargo operations
  • Certain smaller commercial passenger operations

Why Part 135 Matters to Mechanics

Part 135 operators have maintenance requirements that are more structured than basic Part 91 operations.

A mechanic working with a Part 135 operator may need to follow:

  • Approved inspection programs
  • Operator manuals
  • Required maintenance procedures
  • Recordkeeping requirements
  • Airworthiness requirements specific to the operation

Part 135 vs. Part 121

A simple way to remember the difference:

Part 121 is generally airline-type scheduled operations with larger aircraft. Part 135 is generally commuter and on-demand operations.

This is simplified, but useful for A&P study.

Study Points

Remember:

  • Part 135 covers commuter and on-demand operations.
  • Charter and air taxi operations are commonly associated with Part 135.
  • Part 135 operators may have approved maintenance and inspection programs.
  • Mechanics must follow the operator’s approved procedures.

Part 145 — Repair Stations

Part 145 covers FAA-certificated repair stations.

A repair station is an organization certificated by the FAA to perform maintenance, preventive maintenance, or alterations within the ratings and limitations of its certificate.

Why Part 145 Matters to Mechanics

A repair station is not the same thing as an individual mechanic certificate.

The repair station certificate belongs to the organization. The repair station must follow its FAA-approved or FAA-accepted procedures, manuals, ratings, and limitations.

Repair stations may have ratings such as:

  • Airframe
  • Powerplant
  • Propeller
  • Radio
  • Instrument
  • Accessory
  • Limited ratings

Repair Station vs. A&P Mechanic

An A&P mechanic certificate gives privileges to an individual.

A repair station certificate gives privileges to an organization.

A mechanic working at a repair station may perform work under the repair station’s authority and procedures.

Study Points

Remember:

  • Part 145 covers repair stations.
  • A repair station is an FAA-certificated organization.
  • Repair stations have ratings and limitations.
  • Repair stations must follow their manuals and procedures.
  • A repair station certificate is not the same thing as an A&P certificate.

Part 147 — Aviation Maintenance Technician Schools

Part 147 covers Aviation Maintenance Technician Schools, often called AMTS.

This Part is important for students because it governs FAA-certificated A&P schools.

Why Part 147 Matters to A&P Students

If you are attending an FAA-certificated A&P school, that school operates under Part 147.

Part 147 deals with things such as:

  • School certification
  • Curriculum requirements
  • Facilities
  • Equipment
  • Instructors
  • Training records
  • FAA oversight

Part 147 and Mechanic Certification

Completing an FAA-certificated Aviation Maintenance Technician School can be one pathway to meeting the experience requirements for mechanic certification.

However, finishing school is not the same thing as holding an A&P certificate.

The student must still meet FAA testing and certification requirements.

Study Points

Remember:

  • Part 147 covers Aviation Maintenance Technician Schools.
  • AMTS means Aviation Maintenance Technician School.
  • Part 147 schools help students qualify for mechanic testing.
  • Graduation from school is not the same thing as holding an A&P certificate.

How These Regulations Connect for A&P Students

The easiest way to study the FAR-AMTs is to connect them by purpose.

Certification and Design Rules

These Parts explain approved designs and certification standards:

  • Part 21
  • Part 23
  • Part 25
  • Part 27
  • Part 29
  • Part 33
  • Part 35

Maintenance and Airworthiness Rules

These Parts are directly tied to maintenance and airworthiness:

  • Part 39
  • Part 43
  • Part 65
  • Part 91

Aircraft Identification and Registration

These Parts help identify and register aircraft:

  • Part 45
  • Part 47

Commercial Operator Rules

These Parts deal with air carrier and commercial operations:

  • Part 119
  • Part 121
  • Part 125
  • Part 135

Maintenance Organizations and Schools

These Parts cover repair stations and A&P schools:

  • Part 145
  • Part 147

Highest-Priority FAR-AMTs for the A&P Test

All of the Parts in this post are useful, but some are more important for A&P testing than others.

For the A&P written, oral, and practical exams, know these especially well:

  • Part 1 definitions
  • Part 21 certification basics
  • Part 39 Airworthiness Directives
  • Part 43 maintenance and records
  • Part 43 Appendix A
  • Part 43 Appendix B
  • Part 43 Appendix D
  • Part 65 mechanic certification and privileges
  • Part 91 maintenance responsibility, inspections, and records
  • Part 145 repair stations
  • Part 147 AMTS

Quick Memory Aids

Use these to keep the FAR-AMTs straight:

Part 1 = definitions

Part 21 = certification of products and articles

Part 23 = normal category airplanes

Part 25 = transport category airplanes

Part 27 = normal category rotorcraft

Part 29 = transport category rotorcraft

Part 33 = aircraft engines

Part 35 = propellers

Part 39 = Airworthiness Directives

Part 43 = maintenance rules

Part 45 = identification and markings

Part 47 = aircraft registration

Part 65 = mechanic certification

Part 91 = general operating rules and maintenance responsibility

Part 119 = air carrier/commercial operator certification

Part 121 = airline-type operations

Part 125 = certain large-aircraft operations

Part 135 = commuter and on-demand operations

Part 145 = repair stations

Part 147 = Aviation Maintenance Technician Schools

Part 43 Appendix Memory Aids

Appendix A = major alterations, major repairs, and preventive maintenance

Appendix B = recording major repairs and major alterations

Appendix C = reserved

Appendix D = annual and 100-hour inspection scope and detail

Oral Exam Style Questions

What is the difference between FAR and 14 CFR?

FAR is the older/common phrase many aviation people still use. The regulations are officially found in Title 14 of the Code of Federal Regulations, or 14 CFR.

Which Part covers mechanic certification?

Part 65.

Which Part covers maintenance, preventive maintenance, rebuilding, and alterations?

Part 43.

Which Part covers Airworthiness Directives?

Part 39.

Are Airworthiness Directives mandatory?

Yes. ADs are legally enforceable FAA rules.

Which Part places primary responsibility for maintaining an aircraft in airworthy condition on the owner or operator?

Part 91, specifically §91.403.

Which Part covers Aviation Maintenance Technician Schools?

Part 147.

Which Part covers repair stations?

Part 145.

Which Part covers normal category airplanes?

Part 23.

Which Part covers transport category airplanes?

Part 25.

Which Part covers aircraft engines?

Part 33.

Which Part covers propellers?

Part 35.

Which Part covers aircraft identification and registration marking?

Part 45.

Which Part covers aircraft registration?

Part 47.

Which Part 43 Appendix covers preventive maintenance?

Part 43 Appendix A.

Which Part 43 Appendix covers recording major repairs and major alterations?

Part 43 Appendix B.

What is Part 43 Appendix C?

Reserved.

Which Part 43 Appendix covers annual and 100-hour inspection scope and detail?

Part 43 Appendix D.

Final Study Summary

The FAR-AMTs become easier when you stop treating them as random numbers.

They form a system.

Part 1 defines important terms. Part 21 explains certification of aircraft, engines, propellers, and articles. Parts 23, 25, 27, 29, 33, and 35 contain airworthiness standards for different products. Part 39 makes Airworthiness Directives mandatory. Part 43 explains how maintenance is performed and recorded. Part 45 covers markings. Part 47 covers registration. Part 65 explains mechanic certification, ratings, privileges, and limitations. Part 91 explains owner/operator responsibility, inspections, and records. Parts 119, 121, 125, and 135 explain different types of commercial operations. Part 145 covers repair stations. Part 147 covers Aviation Maintenance Technician Schools.

For A&P students, the most important idea is this:

Airworthiness is not just whether the aircraft looks safe. Airworthiness depends on design approval, proper parts, maintenance, inspections, records, AD compliance, mechanic privileges, and owner/operator responsibility.

Learn how the regulations connect, and the FAR-AMTs will start to make sense.

References

  • 14 CFR Part 1 — Definitions and Abbreviations
  • 14 CFR Part 21 — Certification Procedures for Products and Articles
  • 14 CFR Part 23 — Airworthiness Standards: Normal Category Airplanes
  • 14 CFR Part 25 — Airworthiness Standards: Transport Category Airplanes
  • 14 CFR Part 27 — Airworthiness Standards: Normal Category Rotorcraft
  • 14 CFR Part 29 — Airworthiness Standards: Transport Category Rotorcraft
  • 14 CFR Part 33 — Airworthiness Standards: Aircraft Engines
  • 14 CFR Part 35 — Airworthiness Standards: Propellers
  • 14 CFR Part 39 — Airworthiness Directives
  • 14 CFR Part 43 — Maintenance, Preventive Maintenance, Rebuilding, and Alteration
  • 14 CFR Part 45 — Identification and Registration Marking
  • 14 CFR Part 47 — Aircraft Registration
  • 14 CFR Part 65 — Certification: Airmen Other Than Flight Crewmembers
  • 14 CFR Part 91 — General Operating and Flight Rules
  • 14 CFR Part 119 — Certification: Air Carriers and Commercial Operators
  • 14 CFR Part 121 — Operating Requirements: Domestic, Flag, and Supplemental Operations
  • 14 CFR Part 125 — Certification and Operations: Airplanes Having a Seating Capacity of 20 or More Passengers or a Maximum Payload Capacity of 6,000 Pounds or More
  • 14 CFR Part 135 — Operating Requirements: Commuter and On Demand Operations
  • 14 CFR Part 145 — Repair Stations
  • 14 CFR Part 147 — Aviation Maintenance Technician Schools
  • 14 CFR Part 43 Appendix A — Major Alterations, Major Repairs, and Preventive Maintenance
  • 14 CFR Part 43 Appendix B — Recording of Major Repairs and Major Alterations
  • 14 CFR Part 43 Appendix C — Reserved
  • 14 CFR Part 43 Appendix D — Scope and Detail of Items to Be Included in Annual and 100-Hour Inspections