Aeronautical Terms beginning with I
Initial Climb Area (ICA)
An area beginning at the departure end of runway (DER) to provide unrestricted climb to at least 400 feet above DER elevation.
Instrument Approach Waypoint
Fixes used in defining RNAV IAPs, including the feeder waypoint (FWP), the initial approach waypoint (IAWP), the intermediate waypoint (IWP), the final approach waypoint (FAWP), the RWY WP, and the APT WP, when required.
Instrument Landing System (ILS)
A precision instrument approach system that normally consists of the following electronic components and visual aids; localizer, glide slope, outer marker, middle marker, and approach lights.
Instrument Procedure with Vertical Guidance (IPV)
Satellite or Flight Management System (FMS) lateral navigation (LNAV) with computed positive vertical guidance based on barometric or satellite elevation. This term has been renamed APV.
International Civil Aviation Organization (ICAO)
ICAO is a specialized agency of the United Nations whose objective is to develop standard principles and techniques of international air navigation and to promote development of civil aviation.
Intersection
Typically, the point at which two VOR radial position lines cross on a route, usually intersecting at a good angle for positive indication of position, resulting in a VOR/VOR fix.
IFR (Instrument Flight Rules)
Rules that govern the procedure for conducting flight in weather conditions below VFR weather minimums. The term “IFR” also is used to define weather conditions and the type of flight plan under which an aircraft is operating.
Igniter Plugs
The electrical device used to provide the spark for starting combustion in a turbine engine. Some igniters resemble spark plugs, while others, called glow plugs, have a coil of resistance wire that glows red hot when electrical current flows through the coil.
Impact Ice
Ice that forms on the wings and control surfaces or on the carburetor heat valve, the walls of the air scoop, or the carburetor units during flight. Impact ice collecting on the metering elements of the carburetor may upset fuel metering or stop carburetor fuel flow.
Inclinometer
An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.
Indicated Airspeed (IAS)
The direct instrument reading obtained from the airspeed indicator, uncorrected for variations in atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining airplane performance. Takeoff, landing, and stall speeds listed in the AFM or POH are indicated airspeeds and do not normally vary with altitude or temperature.
Indicated Altitude
The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
Induced Drag
That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed.
Induction Manifold
The part of the engine that distributes intake air to the cylinders.
Inertia
The opposition which a body offers to a change of motion.
Initial Climb
This stage of the climb begins when the airplane leaves the ground, and a pitch attitude has been established to climb away from the takeoff area.
Integral Fuel Tank
A portion of the aircraft structure, usually a wing, which is sealed off and used as a fuel tank. When a wing is used as an integral fuel tank, it is called a “wet wing.”
Intercooler
A device used to reduce the temperature of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.
Internal Combustion Engines
An engine that produces power as a result of expanding hot gases from the combustion of fuel and air within the engine itself. A steam engine where coal is burned to heat up water inside the engine is an example of an external combustion engine.
Interstage Turbine Temperature (ITT)
The temperature of the gases between the high pressure and low pressure turbines.
Inverter
An electrical device that changes DC to AC power.
ISA (International Standard Atmosphere)
Standard atmospheric conditions consisting of a temperature of 59°F (15°C), and a barometric pressure of 29.92 in. Hg. (1013.2 mb) at sea level. ISA values can be calculated for various altitudes using a standard lapse rate of approximately 2°C per 1,000 feet.
Ident
Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controllers scope.
ILS categories
Categories of instrument approach procedures allowed at airports equipped with the following types of instrument landing systems: ILS Category I: Provides for approach to a height above touchdown of not less than 200 feet, and with runway visual range of not less than 1,800 feet. ILS Category II: Provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet. ILS Category IIIA: Provides for approach without a decision height minimum and with runway visual range of not less than 700 feet. ILS Category IIIB: Provides for approach without a decision height minimum and with runway visual range of not less than 150 feet. ILS Category IIIC: Provides for approach without a decision height minimum and without runway visual range minimum.
Indicated airspeed (IAS)
Shown on the dial of the instrument airspeed indicator on an aircraft. Directly related to calibrated airspeed (CAS), IAS includes instrument errors and position error.
Indirect indication
A reflection of aircraft pitch-and-bank attitude by the instruments other than the attitude indicator.
Induced drag
Drag caused by the same factors that produce lift; its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, in turn increasing induced drag.
Induction icing
A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.
Inertial navigation system (INS)
A computer-based navigation system that tracks the movement of an aircraft via signals produced by onboard accelerometers. The initial location of the aircraft is entered into the computer, and all subsequent movement of the aircraft is sensed and used to keep the position updated. An INS does not require any inputs from outside signals.
Initial approach fix (IAF)
The fix depicted on IAP charts where the instrument approach procedure (IAP) begins unless otherwise authorized by ATC.
Inoperative components
Higher minimums are prescribed when the specified visual aids are not functioning; this information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications.
Instantaneous vertical speed indicator (IVSI)
Assists in interpretation by instantaneously indicating the rate of climb or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI).
Instrument approach procedures (IAP)
A series of predetermined maneuvers for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.
Instrument flight rules (IFR)
Rules and regulations established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals.
Instrument landing system (ILS)
An electronic system that provides both horizontal and vertical guidance to a specific runway, used to execute a precision instrument approach procedure.
Instrument meteorological conditions (IMC).
Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions, requiring operations to be conducted under IFR.
Instrument takeoff
Using the instruments rather than outside visual cues to maintain runway heading and execute a safe takeoff.
Interference drag
Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.
International Civil Aviation Organization (ICAO)
The United Nations agency for developing the principles and techniques of international air navigation, and fostering planning and development of international civil air transport.
International standard atmosphere (IAS)
A model of standard variation of pressure and temperature.
Inversion illusion
The feeling that the aircraft is tumbling backwards, caused by an abrupt change from climb to straight- and-level flight while in situations lacking visual reference.
Inverter
A solid-state electronic device that converts D.C.
Into A.C
Current of the proper voltage and frequency to operate A.C. gyro instruments.
Isogonic lines
Lines drawn across aeronautical charts to connect points having the same magnetic variation.
Illustrated talk
An oral presentation where the speaker relies heavily on visual aids to convey ideas to the listeners.
Insight
The grouping of perceptions into meaningful wholes. Creating insight is one of the instructor’s major responsibilities.
Instructional aids
Devices that assist an instructor in the teaching-learning process. They are supplementary training devices, and are not self-supporting.
Instrument proficiency check
An evaluation ride based on the instrument rating practical test standard which is required to regain instrument flying privileges when the privileges have expired due to lack of currency.
Integrated flight instruction
A technique of flight instruction in which students are taught to perform flight maneuvers by reference to both the flight instruments and to outside visual references from the time the maneuver is first introduced. Handling of the controls is the same regardless of whether flight instruments or outside references are being used.
Intensity
A principle of learning in which a dramatic or exciting learning experience is likely to be remembered longer than a boring experience. Students experiencing the real thing will learn more than when they are merely told about the real thing.
Interactive video
Software that responds quickly to certain choices and commands by the user. A typical system consists of a compact disk, computer, and video technology.
Interference
(1) A theory of forgetting proposing that a person forgets something because a certain experience overshadows it, or the learning of similar things has intervened. (2) Barriers to effective communication that are caused by physiological, environmental, and psychological factors outside the direct control of the instructor. The instructor must take these factors into account in order to communicate effectively.
Internet
An electronic network that connects computers around the world.
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.
IFR conditions
Weather conditions below the minimum for flight under visual flight rules.
IFR over-the-top
With respect to the operation of aircraft, the operation of an aircraft over-the-top on an IFR flight plan when cleared by air traffic control to maintain “VFR conditions” or “VFR conditions on top”.
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.
Instrument approach procedure (IAP)
A series of predetermined maneuvers by reference to flight instruments with specified protection from obstacles and assurance of navigation signal reception capability. It begins from the initial approach fix, or where applicable, from the beginning of a defined arrival route to a point:
(1) From which a landing can be completed; or
(2) If a landing is not completed, to a position at which holding or en route obstacle clearance criteria apply.
Interstate air commerce
The carriage by aircraft of persons or property for compensation or hire, or the carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or furtherance of a business or vocation, in commerce between a place in any State of the United States, or the District of Columbia, and a place in any other State of the United States, or the District of Columbia; or between places in the same State of the United States through the airspace over any place outside thereof; or between places in the same territory or possession of the United States, or the District of Columbia.
Interstate air transportation
The carriage by aircraft of persons or property as a common carrier for compensation or hire, or the carriage of mail by aircraft in commerce:
(1) Between a place in a State or the District of Columbia and another place in another State or the District of Columbia;
(2) Between places in the same State through the airspace over any place outside that State; or
(3) Between places in the same possession of the United States;
Whether that commerce moves wholly by aircraft of partly by aircraft and partly by other forms of transportation.
Intrastate air transportation
The carriage of persons or property as a common carrier for compensation or hire, by turbojet-powered aircraft capable of carrying thirty or more persons, wholly within the same State of the United States.
Index Point
A location specified by the aircraft manufacturer from which arms used in weight and balance computations are measured. Arms measured from the index point are called index arms.
Interpolate
To determine a value in a series between two known values.
Indicated altitude
The altitude above mean sea level indicated on a pressure altimeter set at current local altimeter setting.
Ice crystals
A type of precipitation composed of unbranched crystals in the form of needles, columns, or plates; usually having a very slight downward motion, may fall from a cloudless sky.
Ice fog
A type of fog composed of minute suspended particles of ice; occurs at very low temperatures and may cause halo phenomena.
Ice needles
A form of ice crystals.
Ice pellets
Small, transparent or translucent, round or irregularly shaped pellets of ice. They may be (1) hard grains that rebound on striking a hard surface or (2) pellets of snow encased in ice.
Icing
In general, any deposit of ice forming on an object. Types include clear icing, rime icing, and glaze.
Indefinite ceiling
A ceiling classification denoting vertical visibility into a surface based obscuration.
Insolation
Incoming solar radiation falling upon the earth and its atmosphere.
Instability
A general term to indicate various states of the atmosphere in which spontaneous convection will occur when prescribed criteria are met; indicative of turbulence. Types include: absolute instability, conditionally unstable air, convective instability.
Intertropical convergence zone
The boundary zone between the trade wind system of the Northern and Southern Hemispheres; it is characterized in maritime climates by showery precipitation with cumulonimbus clouds sometimes extending to great heights.
Inversion
An increase in temperature with height-a reversal of the normal decrease with height in the troposphere; may also be applied to other meteorological properties.
Isobar
A line of equal or constant barometric pressure.
Iso echo
In radar circuitry, a circuit that reverses signal strength above a specified intensity level, thus causing a void on the scope in the most intense portion of an echo when maximum intensity is greater than the specified level.
Isoheight
On a weather chart, a line of equal height; same as contour (1).
Isoline
A line of equal value of a variable quantity, i.e., an isoline of temperature is an isotherm, etc. Isobars (A line of equal or constant barometric pressure.) and isotachs (A line of equal or constant wind speed.) are examples.
Isoshear
A line of equal wind shear.
Isotach
A line of equal or constant wind speed.
Isotherm
A line of equal or constant temperature.
Isothermal
Of equal or constant temperature, with respect to either space or time; more commonly, temperature with height; a zero lapse rate.
Ident
Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controller’s scope.
ILS categories
Categories of instrument approach procedures allowed at airports equipped with the following types of instrument landing systems: ILS Category I: Provides for approach to a height above touchdown of not less than 200 feet, and with runway visual range of not less than 1,800 feet. ILS Category II: Provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet. ILS Category IIIA: Provides for approach without a decision height minimum and with runway visual range of not less than 700 feet. ILS Category IIIB: Provides for approach without a decision height minimum and with runway visual range of not less than 150 feet. ILS Category IIIC: Provides for approach without a decision height minimum and without runway visual range minimum.
ILS Category I
Provides for approach to a height above touchdown of not less than 200 feet, and with runway visual range of not less than 1,800 feet.
ILS Category II
Provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet.
ILS Category IIIA
Provides for approach without a decision height minimum and with runway visual range of not less than 700 feet.
ILS Category IIIB
Provides for approach without a decision height minimum and with runway visual range of not less than 150 feet.
ILS Category IIIC
Provides for approach without a decision height minimum and without runway visual range minimum.
Inclinometer
An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.
Indicated airspeed (IAS)
Shown on the dial of the instrument airspeed indicator on an aircraft. Indicated airspeed (IAS) is the airspeed indicator reading uncorrected for instrument, position, and other errors. Indicated airspeed means 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. Calibrated airspeed (CAS) is IAS corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors.
Indicated altitude
The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
Indirect indication
A reflection of aircraft pitch-and-bank attitude by instruments other than the attitude indicator.
Induced drag
Drag caused by the same factors that produce lift; its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, in turn increasing induced drag.
Induction icing
A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.
Inertial navigation system (INS)
A computer-based navigation system that tracks the movement of an aircraft via signals produced by onboard accelerometers. The initial location of the aircraft is entered into the computer, and all subsequent movement of the aircraft is sensed and used to keep the position updated. An INS does not require any inputs from outside signals.
Initial approach fix (IAF)
The fix depicted on IAP charts where the instrument approach procedure (IAP) begins unless otherwise authorized by ATC.
Inoperative components
Higher minimums are prescribed when the specified visual aids are not functioning; this information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications.
Instantaneous vertical speed indicator (IVSI)
Assists in interpretation by instantaneously indicating the rate of climb or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI).
Instrument approach procedures (IAP)
A series of predetermined maneuvers for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.
Instrument flight rules (IFR)
Rules and regulations established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals.
Instrument landing system (ILS)
An electronic system that provides both horizontal and vertical guidance to a specific runway, used to execute a precision instrument approach procedure.
Instrument meteorological conditions (IMC)
Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions, requiring operations to be conducted under IFR.
Instrument takeoff
Using the instruments rather than outside visual cues to maintain runway heading and execute a safe takeoff.
Intercooler
A device used to reduce the temperatures of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.
Interference drag
Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.
International Civil Aviation Organization (ICAO)
The United Nations agency for developing the principles and techniques of international air navigation, and fostering planning and development of international civil air transport.
International standard atmosphere (IAS)
A model of standard variation of pressure and temperature.
Interpolation
The estimation of an intermediate value of a quantity that falls between marked values in a series. Example: In a measurement of length, with a rule that is marked in eighths of an inch, the value falls between 3/8 inch and 1/2 inch. The estimated (interpolated) value might then be said to be 7/16 inch.
Inversion
An increase in temperature with altitude.
Inversion illusion
The feeling that the aircraft is tumbling backwards, caused by an abrupt change from climb to straight-and-level flight while in situations lacking visual reference.
Inverter
A solid-state electronic device that converts D.C. into A.C. current of the proper voltage and frequency to operate A.C. gyro instruments.
Isobars
Lines which connect points of equal barometric pressure.
Isogonic lines
Lines drawn across aeronautical charts to connect points having the same magnetic variation.
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