Hypoxia.  A state of oxygen deficiency in the body sufficient  to impair functions of the brain and other organs. IAF.  See initial approach fix. IAP.  See instrument approach procedures. IAS.  See indicated airspeed. ICAO.  See International Civil Aviation Organization. Ident. Air Traffic Control request for a pilot to push  the button on the transponder to identify return on the  controller’s scope. IFR.  See instrument flight rules. ILS.  See instrument landing system. ILS categories. Categories of instrument approach  procedures allowed at airports equipped with the following  types of instrument landing systems: IMC.  See instrument meteorological conditions. 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. 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 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 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 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. 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). INS.  See inertial navigation system. 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. Initial approach fix (IAF).  The fix depicted on IAP charts  where the instrument approach procedure (IAP) begins unless  otherwise authorized by ATC. 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. G-9 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.