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).  G-9