effect, there is a reduction in upwash, downwash, and wingtip vortices. As a result of the reduced wingtip vortices, induced drag is reduced. 

Ground track.  The aircraft’s path over the ground when in flight. 

Ground wires.  The wires on top of the wing attached to the king post which hold up the wings on the ground and during negative loads during flight. The fore to aft ground wires which hold the king post in place fore to aft. 

Groundspeed (GS) . The actual speed of an aircraft over the ground. It is true airspeed adjusted for wind. Groundspeed decreases with a headwind, and increases with a tailwind. A GPS measures ground speed. 

Hazardous Inflight Weather Advisory Service (HIWAS). Recorded weather forecasts broadcast to airborne pilots over selected VORs. 

Heading.  The direction in which the nose of the aircraft is pointing during flight. 

Headwind. A wind which blows from the direction the aircraft is flying. The ground speed of an aircraft (the speed the aircraft is moving over the ground) is less than the speed through the air by the velocity of the headwind. 

Headwind component. The component of atmospheric winds that acts opposite to the aircraft’s flightpath. 

HIWAS.  See Hazardous Inflight Weather Advisory Service. 

Horsepower.  The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute. 

Hour meter. An instrument installed in many aircraft to show the actual number of hours the engine has operated. 

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. 

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.  State of oxygen deficiency in the body sufficient to impair functions of the brain and other organs. 

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. 

IMC. See instrument meteorological conditions. 

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. 

Incident. An occurrence other than an accident, associated with the operation of an aircraft, which affects or could affect the safety of operations. 

Induced drag.  That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed. 

Instrument flight rules (IFR).  Rules governing the procedures for conducting instrument flight. Also a term used by pilots and controllers to indicate type of flight plan. 

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). 

