Aviation Maintenance Terms beginning with I
Improper fraction
A fraction with the numerator equal to or greater than the denominator.
Inside calipers
Calipers with outward curved legs for measuring inside diameters, such as diameters of holes.
Installation drawing
A drawing that includes all necessary information for a part or an assembly in the final installed position in the aircraft.
Intergranular corrosion
An attack along the grain boundaries of an alloy that commonly results from a lack of uniformity in the alloy structure.
Inductance
The ability of a coil or conductor to oppose a change in current flow.
Inductive reactance
The opposition to the flow of current which inductances put in a circuit.
Inductor
A coil of wire that produces inductance in an electrical circuit.
Insulator
A material that does not conduct electrical current very well or not at all. Examples are glass, ceramic, and plastic.
Ion
An atom or group of atoms in which the number of electrons is different from the number of protons. It is a positive ion if the number of electrons is less than the number of protons, and a negative ion if the number of electrons is greater than the number of protons.
Isometric drawings
A drawing that uses a combination of the views of an orthographic projection and tilts the object forward so that portions of all three views can be seen in one view
Ice bridging
A spark plug failure that occurs when starting a reciprocating engine in extremely cold weather. When a cylinder fires, the air/fuel mixture is converted into carbon dioxide and water vapor. The water vapor condenses on the spark plug electrodes and forms ice that bridges the electrode gap and prevents the plug firing until the ice is melted. This normally requires removing the spark plugs from the engine.
Igniter
The component in a turbine-engine ignition system that provides a high-energy spark for igniting the air/fuel mixture in the combustion chamber for starting.
Impulse coupling
A spring-loaded coupling between a magneto shaft and the drive gear inside the engine. When the engine is rotated for starting, the impulse coupling locks the magnet so it cannot turn. The spring in the coupling winds up as the crankshaft continues to turn, and when the piston is near top center, the coupling releases and spins the magnet, producing a hot and retarded spark.
Inline engine
A reciprocating engine with all of the cylinders arranged in a straight line.
Incandescent
Glowing because of intense heat.
Inconel
The registered trade name for an alloy of chromium, iron, and nickel. Inconel is similar to stainless steel, but cannot be hardened by heat treatment.
Inductive reactance
An opposition to the flow of AC or changing DC caused by inductance in the circuit. Inductive reactance, whose symbol is XL, causes a voltage drop, but it does not use power nor produce heat.
Inertia
The tendency of a body to resist acceleration. A body at rest will remain at rest or a body in motion will stay in motion in a straight line unless acted on by an outside force.
Inertia starter
A starter for a large reciprocating engine that uses energy stored in a rapidly spinning flywheel to turn the crankshaft.
Inlet guide vanes
A set of stator vanes in front of the first stage of compression in a gas turbine engine. The inlet guide vanes deflect the air entering the compressor in the correct direction for optimum operation. Inlet guide vanes may be fixed, or their angle may be controlled hydraulically by fuel from the fuel control.
Integral fuel tank
An aircraft fuel tank made by sealing off part of the structure so fuel can be carried in the structure itself.
Intercooler
An air-to-air heat exchanger installed between a turbosupercharger and the carburetor. Intercoolers decrease the temperature of compressed air to prevent detonation.
Interference angle (poppet valve dimension)
The difference between the valve seat and the valve face angles. Normally, the valve seats are ground with between 0.5° and 1° greater angle than the valve face. This allows the face to touch the seat with a line contact that provides the best sealing.
Interference fit
A type of fit used when assembling certain mechanical devices. The hole is made smaller than the part that fits into it. The material containing the hole is heated to expand the hole, and the part that fits into the hole is chilled to shrink it. The parts are assembled, and when they reach the same temperature their fit is so tight they will not loosen in service.
Internal-combustion engine
A form of heat engine in which the fuel and air mixture is burned inside the engine to heat and expand the air so it can perform useful work.
Internal timing
The adjustment of the breaker points of a magneto so they will begin to open at the time the magnet is in its E-gap position.
Interpole
A field pole in a compound-wound DC generator used to minimize armature reaction. Interpoles are located between each of the regular field poles, and their coils are in series with the armature winding so all of the armature current flows through them. The magnetic field produced by the interpole coils cancels the distortion caused by the armature field and allows the brushed to remain in the neutral plane where there is no potential difference between the commutator segments. Keeping the brushes in the neutral plane minimizes sparking.
Inverted engine
An inline or V-engine in which the cylinders are mounted below the crankshaft.
Iridium
A very hard, brittle, highly corrosion-resistant, whitish-yellow, metallic chemical element. Iridium is used for the fine-wire electrodes in spark plugs that must operate in engines using fuel with an exceptionally high lead content.
Iso-octane
An organic compound used as the high reference fuel for rating the antidetonation characteristics of aviation gasoline (CH3)2CHCH2C(CH3)3.
Isothermal change
A physical change that takes place within a material in which heat energy is added to or taken from the material as needed to keep its temperature constant.
Icebox rivet
A solid rivet made of 2017 or 2024 aluminum alloy. These rivets are too hard to drive in the condition they are received from the factory, and must be heat-treated to soften them. They are heated in a furnace and then quenched in cold water. Immediately after quenching they are soft, but within a few hours at room temperature they become quite hard. The hardening can be delayed for several days by storing them in a subfreezing icebox and holding them at this low temperature until they are to be used.
Inch-pound
A measure of work accomplished when a force of 1 pound moves an object a distance of 1 inch.
Indicated airspeed (IAS)
The airspeed as shown on an airspeed indicator with no corrections applied.
Induced current
Electrical current produced in a conductor when it is moved through or crossed by a magnetic field.
Induced drag
Aerodynamic drag produced by an airfoil when it is producing lift. Induced drag is affected by the same factors that affect induced lift.
Induction time
The time allowed an epoxy or polyurethane material between its initial mixing and its application. This time allows the materials to begin their cure.
Infrared radiation
Electromagnetic radiation whose wavelengths are longer than those of visible light.
Ingot
A large block of metal that was molded as it was poured from the furnace. Ingots are further processed into sheets, bars, tubes, or structural beams.
Inspection Authorization (IA)
An authorization that may be issued to an experienced aviation maintenance technician who holds both an Airframe and Powerplant rating. It allows the holder to conduct annual inspections and to approve an aircraft or aircraft engine for return to service after a major repair or major alteration.
Integral fuel tank
A fuel tank which is formed by sealing off part of the aircraft structure and using it as a fuel tank. An integral wing tank is called a “wet wing.” Integral tanks are used because of their large weight saving. The only way of repairing an integral fuel tank is by replacing damaged sealant and making riveted repairs, as is done with any other part of the aircraft structure.
Interference drag
Parasite drag caused by air flowing over one portion of the airframe interfering with the smooth flow of air over another portion.
Intermittent-duty solenoid
A solenoid-type switch whose coil is designed for current to flow through it for only a short period of time. The coil will overheat if current flows through it too long.
Iso-octane
A hydrocarbon, C8H18, which has very high critical pressure and temperature. Iso-octane is used as the high reference for measuring the antidetonation characteristics of a fuel.
Isobaric mode
The mode of pressurization in which the cabin pressure is maintained at a constant value regardless of the outside air pressure.
Isogonic line
A line drawn on an aeronautical chart along which the angular difference between the magnetic and geographic north poles is the same.
Isopropyl alcohol
A colorless liquid used in the manufacture of acetone and its derivatives and as a solvent and anti-icing agent.
Idle thrust
The jet thrust obtained with the engine power control level set at the stop for the least thrust position at which it can be placed.
Indicated airspeed
The speed of an aircraft as shown on its pitot static airspeed indicator calibrated to reflect standard atmosphere adiabatic compressible flow at sea level uncorrected for airspeed system errors.
In-flight shutdown (IFSD)
For ETOPS only, when an engine ceases to function (when the airplane is airborne) and is shutdown, whether self induced, flightcrew initiated or caused by an external influence. The FAA considers IFSD for all causes: for example, flameout, internal failure, flightcrew initiated shutdown, foreign object ingestion, icing, inability to obtain or control desired thrust or power, and cycling of the start control, however briefly, even if the engine operates normally for the remainder of the flight. This definition excludes the airborne cessation of the functioning of an engine when immediately followed by an automatic engine relight and when an engine does not achieve desired thrust or power but is not shutdown.
Instrument
A device using an internal mechanism to show visually or aurally the attitude, altitude, or operation of an aircraft or aircraft part. It includes electronic devices for automatically controlling an aircraft in flight.
Inductance (L)
The ability of a coil or conductor to oppose a change in current flow.
Insulator
A material that will not conduct current to an appreciable degree.
Integrated circuit
Small, complete circuit built up by vacuum deposition and other techniques, usually on a silicon chip, and mounted in a suitable package.
Intergranular corrosion
The formation of corrosion along the grain boundaries within a metal alloy.
Interlocked-grained wood
Wood in which the fibers are inclined in one direction in a number of rings of annual growth, then gradually reverse and are inclined in an opposite direction in succeeding growth rings, then reverse again.
Inverter
A device for converting direct current to alternating current.
International Civil Aviation Organization (ICAO)
A United Nations organization that is responsible for developing international standards, and recommending practices, and procedures covering a variety of technical fields of aviation.
In-Trail Procedure (ITP)
A procedure that allows an aircraft to climb-through or descend-through another aircraft’s altitude in order to make a desired flight level change.
Innerliner
The integral rubber lining of a tubeless tire that is engineered to prevent the diffusion of the inflation gas into the casing.
Innertube
A gas-tight rubber device placed inside a tube-type tire casing for the purpose of containing the inflation gas. It is provided with an integral valve assembly.
Impact damage
Damage (visible or not) resulting from a blade striking or being struck, while in flight or on the ground, by an object such as a snow bank, runway light, maintenance stand, birds, etc.
Inclusion
Material foreign to base metal but contained in it.