Glossary

Indirect indication. A reflection of aircraft pitch-and-bank Instrument meteorological conditions (IMC). attitude by instruments other than the attitude indicator. Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums Induced drag. Drag caused by the same factors that produce specified for visual meteorological conditions, requiring lift; its amount varies inversely with airspeed. As airspeed operations to be conducted under IFR. decreases, the angle of attack must increase, in turn increasing induced drag. Instrument takeoff. Using the instruments rather than outside visual cues to maintain runway heading and execute Induction icing. A type of ice in the induction system that a safe takeoff. reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing. Intercooler. A device used to reduce the temperatures of the compressed air before it enters the fuel metering device. The Inertial navigation system (INS). A computer-based resulting cooler air has a higher density, which permits the navigation system that tracks the movement of an aircraft engine to be operated with a higher power setting. via signals produced by onboard accelerometers. The initial location of the aircraft is entered into the computer, and all Interference drag. Drag generated by the collision of subsequent movement of the aircraft is sensed and used to airstreams creating eddy currents, turbulence, or restrictions keep the position updated. An INS does not require any inputs to smooth flow. from outside signals. International Civil Aviation Organization (ICAO). The Initial approach fix (IAF). The fix depicted on IAP charts United Nations agency for developing the principles and where the instrument approach procedure (IAP) begins unless techniques of international air navigation, and fostering otherwise authorized by ATC. planning and development of international civil air transport. Inoperative components. Higher minimums are prescribed International standard atmosphere (IAS). A model of when the specified visual aids are not functioning; this standard variation of pressure and temperature. information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications. Interpolation. The estimation of an intermediate value of a quantity that falls between marked values in a series. INS. See inertial navigation system. Example: In a measurement of length, with a rule that is marked in eighths of an inch, the value falls between 3/8 Instantaneous vertical speed indicator (IVSI). Assists in inch and 1/2 inch. The estimated (interpolated) value might interpretation by instantaneously indicating the rate of climb then be said to be 7/16 inch. or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI). Inversion. An increase in temperature with altitude. Instrument approach procedures (IAP). A series of Inversion illusion. The feeling that the aircraft is tumbling predetermined maneuvers for the orderly transfer of an backwards, caused by an abrupt change from climb to straight- aircraft under IFR from the beginning of the initial approach and-level flight while in situations lacking visual reference. to a landing or to a point from which a landing may be made visually. Inverter. A solid-state electronic device that converts D.C. into A.C. current of the proper voltage and frequency to Instrument flight rules (IFR). Rules and regulations operate A.C. gyro instruments. established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual Isobars. Lines which connect points of equal barometric reference is not safe. IFR flight depends upon flying by pressure. reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals. Isogonic lines. Lines drawn across aeronautical charts to connect points having the same magnetic variation. Instrument landing system (ILS). An electronic system that provides both horizontal and vertical guidance to a IVSI. See instantaneous vertical speed indicator. specific runway, used to execute a precision instrument approach procedure. G-16