Aeronautical Terms beginning with I


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.


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.

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