Human factors.  A multidisciplinary field encompassing the  behavioral and social sciences, engineering, and physiology,  to consider the variables that influence individual and  crew performance for the purpose of optimizing human  performance and reducing errors.  Ident.  Air Traffic Control request for a pilot to push  the button on the transponder to identify return on the  controller’s scope.  Hung start.  In gas turbine engines, a condition of normal  light off but with rpm remaining at some low value rather than  increasing to the normal idle rpm. This is often the result of  insufficient power to the engine from the starter. In the event  of a hung start, the engine should be shut down.  Hydroplaning.  A condition that exists when landing on a  surface with standing water deeper than the tread depth of  the tires. When the brakes are applied, there is a possibility  that the brake will lock up and the tire will ride on the  surface of the water, much like a water ski. When the tires  are hydroplaning, directional control and braking action  are virtually impossible. An effective anti-skid system can  minimize the effects of hydroplaning.  Hypemic hypoxia.  A type of hypoxia that is a result of  oxygen deficiency in the blood, rather than a lack of inhaled  oxygen. It can be caused by a variety of factors. Hypemic  means “not enough blood.”  Hyperventilation.  Occurs when an individual is experiencing  emotional stress, fright, or pain, and the breathing rate and  depth increase, although the carbon dioxide level in the  blood is already at a reduced level. The result is an excessive  loss of carbon dioxide from the body, which can lead to  unconsciousness due to the respiratory system’s overriding  mechanism to regain control of breathing.  Hypoxia.  A state of oxygen deficiency in the body sufficient  to impair functions of the brain and other organs.  Hypoxic hypoxia.  This type of hypoxia is a result of  insufficient oxygen available to the lungs. A decrease of  oxygen molecules at sufficient pressure can lead to hypoxic  hypoxia.  IAF.  See initial approach fix.  IAP.  See instrument approach procedures.  IAS.  See indicated airspeed.  ICAO.  See International Civil Aviation Organization.  Indicated altitude.  The altitude read directly from the  altimeter (uncorrected) when it is set to the current altimeter  setting.  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.  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.  IMC.  See instrument meteorological conditions.  ILS categories.  Categories of instrument approach  procedures allowed at airports equipped with the following  types of instrument landing systems:  ILS.  See instrument landing system.  IFR.  See instrument flight rules.  G-15  I  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. 