Aviation Maintenance Glossary: 50+ FAA A&P Terms Every Mechanic Should Know
Every industry has its own language, and aviation maintenance is no exception. From regulatory acronyms to technical manual designations, the terms you encounter as an A&P mechanic candidate can be overwhelming at first. This glossary defines essential terms with clear explanations and real-world context — helping you decode the documents, pass your FAA knowledge tests, and talk the talk on the hangar floor.
SkyLicense Team
FAA A&P exam preparation specialists — helping mechanics earn their Airframe & Powerplant certificate since 2025
Whether you are preparing for the FAA knowledge tests, reading an AMM for the first time, or trying to understand a DER-approved repair disposition, this glossary will help you cut through the jargon. Each entry includes a concise definition and a real-world usage context so you understand not just what the term means, but how it applies in your daily work as an A&P mechanic.
For exam-specific preparation resources, see our A&P written test study guide, Airframe written test FAQ, and FAA A&P study plan.
A
AC (Advisory Circular)
An informational document issued by the FAA that provides guidance on acceptable methods, techniques, and practices for complying with regulations. Advisory circulars are not mandatory, but they describe "acceptable means of compliance." AC 43.13-1B is the most important AC for A&P mechanics — it covers standard inspection and repair methods for aircraft structures.
Context: Used as acceptable data when performing structural repairs. Following an AC is generally accepted as compliance with the underlying regulation.
AC 43.13-1B
The FAA Advisory Circular titled "Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair." The definitive reference for sheet metal repair, welding, corrosion treatment, composite repair, and non-destructive testing. It is widely used by mechanics and Designated Engineering Representatives (DERs) as acceptable data for repairs.
Context: Every A&P mechanic should own a copy. Frequently referenced in the General and Airframe knowledge tests and in daily repair work.
AD (Airworthiness Directive)
A legally enforceable rule issued by the FAA (14 CFR Part 39) requiring mandatory action on an aircraft, engine, propeller, or component. ADs address known safety deficiencies and may require inspection, modification, replacement, or operational limitations. Compliance is mandatory regardless of other maintenance schedules.
Context: Compliance with ADs must be recorded in the aircraft maintenance records with the AD number, method of compliance, and signature. Tracking AD compliance is a core A&P responsibility.
AMM (Aircraft Maintenance Manual)
The manufacturer-issued manual containing step-by-step maintenance, inspection, and repair procedures for a specific aircraft model. The AMM is the primary source of data for scheduled and unscheduled maintenance and must be current and available whenever maintenance is performed.
Context: Performing maintenance without following the applicable AMM data is a violation of 14 CFR 43.13. The AMM must be revised to the latest level.
A&P (Airframe & Powerplant)
The FAA mechanic certificate that authorizes the holder to perform and approve maintenance on airframes and powerplants, per 14 CFR Part 65 Subpart D. To qualify, applicants need 18 months of practical experience for one rating or 30 months for both, passing knowledge tests in General, Airframe, and Powerplant, and passing an oral and practical exam with a Designated Mechanic Examiner.
Context: The A&P certificate is the most common FAA mechanic certificate. It authorizes return-to-service sign-offs on the airframe and powerplant ratings held.
APU (Auxiliary Power Unit)
A small gas turbine engine mounted in the aircraft (usually in the tail cone) that provides electrical and pneumatic power when the main engines are not running. Used for ground operations, engine starting, and air conditioning.
Context: Maintenance of APUs falls under the powerplant rating. APUs have their own maintenance schedules and component lives.
ATA Chapters
The Air Transport Association (now Airlines for America) standardized numbering system for aircraft maintenance documentation. Each aircraft system is assigned a chapter number — e.g., ATA 32 for Landing Gear, ATA 72 for Turbine Engine, ATA 21 for Air Conditioning. The ATA iSpec 2200 specification governs this standard.
Context: Every A&P mechanic must know ATA chapter numbers to navigate maintenance manuals efficiently. ATA chapter references appear on virtually every maintenance document.
B
Borescope Inspection
A non-destructive inspection method using a flexible or rigid optical probe (borescope) to examine internal surfaces of engines, components, and structures without disassembly. Essential for turbine engine hot-section inspections.
Context: Commonly used during scheduled engine inspections to check compressor and turbine blades for cracks, burning, and FOD damage.
C
CFR (Code of Federal Regulations)
The codified federal regulations of the United States. For aviation maintenance, the key parts are 14 CFR Part 1 (Definitions), Part 21 (Certification Procedures), Part 39 (Airworthiness Directives), Part 43 (Maintenance, Preventive Maintenance, Rebuilding, and Alteration), Part 65 (Certification: Airmen Other Than Flight Crewmembers — includes mechanics), Part 91 (General Operating and Flight Rules — includes inspection requirements), and Part 145 (Repair Stations).
Context: The FAA knowledge tests reference specific CFR sections. Knowing which Part governs which activity is foundational for every A&P mechanic.
14 CFR Part 43
The regulation governing maintenance, preventive maintenance, rebuilding, and alteration of aircraft. It defines who may perform maintenance (certificated mechanics and repair stations), performance rules (43.13), records requirements (43.9), and the content of annual and 100-hour inspection reports (43.11).
Context: Part 43 is the legal backbone of everyday A&P work. Every logbook entry you sign is governed by its records requirements.
14 CFR Part 65
The regulation governing certification of airmen other than flight crewmembers. Subpart D covers mechanic certification: eligibility (65.71), experience (65.77), knowledge and skill tests, privileges (65.85), and limitations. Subpart E covers Inspection Authorization (IA).
Context: Part 65 defines what an A&P mechanic is authorized to do — and the limits of that authority. Every candidate should know the eligibility and privilege sections.
14 CFR Part 91
The regulation governing general operating and flight rules, including the maintenance and inspection requirements for most civil aircraft: 91.403 (general maintenance), 91.407 (operation after maintenance), 91.409 (annual and 100-hour inspections), and 91.411/91.413 (altimeter, pitot-static, and transponder checks).
Context: Part 91 establishes the annual and 100-hour inspection requirements that drive much of general aviation maintenance work.
CDL (Configuration Deviation List)
A document approved by the FAA that lists non-essential airframe or engine components that may be missing or inoperative for a limited period. The CDL is aircraft-specific and supplements the MEL.
Context: A missing fairing or access panel may be permissible under the CDL, but only for a specified period. The mechanic must document the deviation per the operator procedures.
D
DER (Designated Engineering Representative)
An individual authorized by the FAA to approve engineering data on behalf of the agency. DERs approve STCs, field approvals, repair designs, and data for major repairs and alterations under their designated authority.
Context: When a structural repair exceeds the limits of the SRM or AMM, a DER must approve the engineering disposition.
DME (Designated Mechanic Examiner)
An individual designated by the FAA to administer the oral and practical (O&P) exam for mechanic applicants, using the Aviation Mechanic Airman Certification Standards (ACS). The DME evaluates hands-on skills and oral knowledge across the General, Airframe, and Powerplant areas.
Context: After passing your knowledge tests and presenting FAA Form 8610-2, the DME is the person who administers your O&P and recommends you for certification.
E
EFIS (Electronic Flight Instrument System)
A glass cockpit system that replaces traditional analog flight instruments with electronic displays. EFIS includes Primary Flight Display (PFD), Navigation Display (ND), and Engine Indication and Crew Alerting System (EICAS).
Context: A&P mechanics work on EFIS installation and power supply issues; deep avionics repair typically falls to certificated repair stations.
EGT (Exhaust Gas Temperature)
A critical engine instrument measuring the temperature of exhaust gases. For turbine engines, EGT is a primary indicator of engine health and is monitored during start (hot starts) and throughout operation. For reciprocating engines, EGT is used for leaning the mixture.
Context: Abnormal EGT readings — such as a slow rise on start indicating a hot start — are key troubleshooting signals on both engine types.
F
FAA Form 337
The Major Repair and Alteration form required by 14 CFR 43.9 for major repairs and major alterations. It documents what was done, the data used, and who performed and approved the work. One copy goes to the FAA, one stays in the aircraft permanent records.
Context: Filling out FAA Form 337 correctly is a core skill. The form references the approved data (AC 43.13-1B, SRM, STC, DER data) used for the repair or alteration.
FAA Form 8610-2
The "Airman Certificate and/or Rating Application" used for mechanic certification. Applicants present this form, with proof of passing knowledge tests, to a DME or FAA office to schedule the oral and practical exam.
Context: You need 8610-2 with the knowledge test results and experience documentation before you can take the O&P. It is the gateway to your A&P certificate.
FOD (Foreign Object Debris/Damage)
Any foreign object (tools, hardware, debris) left in or near an aircraft that can cause damage to engines, systems, or structures. FOD is a critical safety concern in all maintenance environments.
Context: FOD prevention programs are mandatory at all repair stations. Tool control, FOD walks, and zoned inspections are standard procedures.
G
GSE (Ground Support Equipment)
Equipment used to service and maintain aircraft on the ground, including tow tractors, power carts, nitrogen carts, hydraulic test stands, engine stands, and maintenance platforms. GSE must be maintained and calibrated as part of the repair station quality system.
Context: Proper GSE operation and maintenance is critical — poorly maintained GSE can damage aircraft just as easily as poor maintenance can.
H
HPT (High Pressure Turbine)
The section of a gas turbine engine immediately downstream of the combustion chamber. The HPT extracts energy from the hot gas flow to drive the high-pressure compressor. HPT blades operate under extreme thermal and mechanical stress.
Context: HPT inspection intervals are governed by airworthiness limitations and ADs. Borescope inspection of HPT blades is a critical scheduled maintenance task on all turbine engines.
I
IA (Inspection Authorization)
An FAA authorization, held in addition to an A&P certificate, that permits a mechanic to perform annual inspections and approve major repairs and alterations for return to service. Governed by 14 CFR 65.91–65.95, the IA requires 24 months of maintenance experience and passing a written test.
Context: Only an IA can sign off annual inspections on non-common-carriage aircraft. Many A&P mechanics pursue the IA to expand their career options.
IPC (Illustrated Parts Catalog)
A manufacturer-issued document containing exploded-view diagrams and parts lists for an aircraft, engine, or component. The IPC is used to identify and order correct replacement parts with the proper part numbers.
Context: Every A&P mechanic uses the IPC regularly to verify part numbers during installations. Using the wrong part number can have serious consequences.
IFSD (In-Flight Shutdown)
An engine shutdown that occurs in flight, either automatically or by crew action, due to a malfunction. IFSD rate is a key reliability metric for engines and airlines.
Context: IFSD events trigger mandatory investigation and reporting requirements under the operator maintenance program.
M
Magneto
A self-contained engine-driven electrical generator that produces the high voltage for spark plugs in reciprocating engines, independent of the aircraft electrical system. Key components include the permanent magnet rotor, coil, breaker points, condenser, and distributor. High-tension magnetos with impulse couplings are standard on general aviation engines.
Context: Magneto timing (E-gap), magneto-to-engine timing, and impulse coupling checks are classic Powerplant test topics and routine maintenance tasks.
MEL (Minimum Equipment List)
A document approved by the FAA that lists specific equipment that may be inoperative for a defined period while maintaining safe operations. The MEL is aircraft-specific and derived from the Master Minimum Equipment List (MMEL).
Context: When an MEL item is deferred, the mechanic must placard the inoperative equipment and make the appropriate maintenance record entry. MEL deferrals are temporary.
MMEL (Master Minimum Equipment List)
The baseline document developed by the aircraft manufacturer and approved by the FAA that establishes minimum operating equipment for the aircraft type. Each operator develops their specific MEL from the MMEL.
Context: The MMEL is more restrictive than the operator MEL — operators may add items but cannot remove items from the MMEL.
MRO (Maintenance, Repair, and Overhaul)
An organization certified to perform maintenance, repair, and overhaul services on aircraft, engines, and components. MROs range from small general aviation shops to large facilities like AAR, StandardAero, and Lufthansa Technik.
Context: MROs are certified under 14 CFR Part 145. Major MROs hold multiple certifications including FAA, EASA, and other national approvals.
N
NDT / NDI (Non-Destructive Testing / Inspection)
Inspection techniques that evaluate material properties and detect defects without damaging the component. Common NDT methods include visual, dye penetrant, magnetic particle, eddy current, ultrasonic, and radiographic (X-ray) inspection, as detailed in AC 43.13-1B Chapter 5.
Context: NDT is essential for crack detection in landing gear, engine components, and airframe structures. NDT certification (per NAS 410 or SNT-TC-1A) is separate from the A&P certificate.
O
OEM (Original Equipment Manufacturer)
The company that designed and manufactured the aircraft, engine, or component. OEMs produce maintenance manuals, parts catalogs, and service bulletins. Examples include Boeing, Airbus, Pratt & Whitney, Honeywell, and Collins Aerospace.
Context: OEM-approved data takes precedence over other maintenance instructions. Mechanics must follow the OEM AMM and IPC.
P
PMA (Parts Manufacturer Approval)
An FAA approval that allows a manufacturer to produce replacement parts for a type-certificated product. PMA parts are functionally equivalent to OEM parts and must meet the same airworthiness standards (14 CFR Part 21 Subpart K).
Context: PMA parts are commonly used as cost-effective alternatives to OEM parts. Mechanics must verify that the PMA part is approved for the specific application.
PSI
The FAA-authorized testing vendor that administers airman knowledge tests, including the General, Airframe, and Powerplant mechanic tests. Tests are computer-based at PSI testing centers across the country, and results are valid for 24 months.
Context: You schedule your knowledge tests directly through PSI. Bring valid identification, and know that a failed test requires a 30-day wait before retaking.
R
RII (Required Inspection Item)
A maintenance task that requires an independent inspection by a second qualified inspector before the aircraft can return to service. RII items are critical to flight safety — examples include flight control rigging, engine installation, and landing gear retraction tests. Required under 14 CFR 121/135 and Part 145 quality programs.
Context: RII programs are part of the approved maintenance organization quality system. Performing an RII task without the required independent inspection is a serious violation.
RTS (Return to Service)
The formal process of releasing an aircraft back to operational service after maintenance. Return to service requires proper maintenance record entries per 14 CFR 43.9, including a signature and certificate number, and compliance with any applicable inspections per 43.11.
Context: No aircraft may operate after maintenance without the proper return-to-service entries. The mechanic who signs assumes legal responsibility for the work.
S
SB (Service Bulletin)
A manufacturer-issued document that provides recommendations for product improvement, modification, or enhanced inspection. Unlike Airworthiness Directives, SBs are generally not mandatory unless specifically required by an AD or the operator maintenance program.
Context: Many operators choose to comply with SBs proactively. Some SBs become mandatory when they are incorporated into an AD.
SRM (Structural Repair Manual)
The manufacturer-issued manual that provides data for structural repairs on a specific aircraft model. The SRM defines damage limits, repair schemes, material specifications, and allowable loads for structural repairs.
Context: Repairs within SRM limits can be performed using the SRM as data. Repairs exceeding SRM limits require DER-approved engineering dispositions.
STC (Supplemental Type Certificate)
An FAA approval to modify an aircraft, engine, or component from its original design configuration. STCs cover modifications like avionics upgrades, interior reconfigurations, engine changes, and cargo conversions.
Context: Mechanics installing STC modifications must follow the STC installation instructions exactly. The STC becomes part of the aircraft approved type design.
T
TBO (Time Between Overhauls)
The manufacturer-recommended interval (in flight hours, cycles, or calendar time) between major overhauls of an engine, component, or accessory. TBO intervals are established based on reliability data and may be extended under engine health monitoring programs.
Context: Exceeding TBO renders the component unairworthy unless an approved TBO extension program is in place. TBO compliance is tracked in the maintenance program.
Turbine Spool
A rotating assembly in a gas turbine engine consisting of a compressor stage and a turbine stage connected by a shaft. Most turbine engines have two spools (N1 low-pressure and N2 high-pressure), and some large engines have three (N1, N2, N3). Each spool rotates at its own speed, indicated by its own tachometer reading.
Context: Understanding spool configurations — including which compressor and turbine sections drive which — is core Powerplant knowledge for turbine engine troubleshooting.
TSO (Technical Standard Order)
A minimum performance standard issued by the FAA for specific aircraft components and materials. Components manufactured to a TSO (e.g., TSO-C112 for Mode S transponders) are accepted as meeting regulatory requirements for their installation.
Context: TSO-marked components are interchangeable and do not require individual airworthiness approval for each installation.
W
W&B (Weight and Balance)
The calculation of aircraft weight and center of gravity position to ensure the aircraft remains within certified limits. Weight and balance data must be updated after any modification, repair, or equipment change that affects aircraft weight.
Context: Mechanics performing modifications must update W&B data. The W&B report is part of the aircraft permanent records and must be current.
Keep Learning with SkyLicense
This glossary is just the beginning. SkyLicense offers AI-powered exam preparation for the FAA A&P certificate, with complete coverage of the General, Airframe, and Powerplant knowledge tests based on the Aviation Mechanic ACS. Our adaptive learning platform helps you master aviation terminology, regulations, and technical concepts through targeted practice questions and instant feedback.
FAA A&P Written Test Study Guide — Complete preparation strategy, from 8610-2 to the O&P
FAA A&P Study Plan (30–60 Days) — A structured schedule for all three knowledge tests
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