Head-up Guidance System (HGS). A system that projects  critical flight data on a display positioned between the pilot  and the windscreen. In addition to showing primary flight  information, the HUD computes an extremely accurate  instrument approach and landing guidance solution, and  displays the result as a guidance cue for head-up viewing  by the pilot.  Height Above Touchdown (HAT). The height of the DA  above touchdown zone elevation (TDZE).  Highway in the Sky (HITS). A graphically intuitive pilot  interface system that provides an aircraft operator with all  of the attitude and guidance inputs required to safely fly  an aircraft in close conformance to air traffic procedures.  Initial Climb Area (ICA). An area beginning at the departure  end of runway (DER) to provide unrestricted climb to at  least 400 feet above DER elevation.  Instrument Approach Waypoint. Fixes used in defining  RNAV IAPs, including the feeder waypoint (FWP), the initial  approach waypoint (IAWP), the intermediate waypoint  (IWP), the final approach waypoint (FAWP), the RWY WP,  and the APT WP, when required.  Instrument Landing System (ILS). A precision instrument  approach system that normally consists of the following  electronic components and visual aids: localizer, glide  slope, outer marker, middle marker, and approach lights.  Instrument Procedure with Vertical Guidance (IPV). Satellite  or flight management system (FMS) lateral navigation  (LNAV) with computed positive vertical guidance based  on barometric or satellite elevation. This term has been  renamed APV.  ICAO is a specialized agency of the United Nations whose  objective is to develop standard principles and techniques  of international air navigation and to promote development  of civil aviation.  Intersection. Typically, the point at which two VOR radial  position lines cross on a route, usually intersecting at a good  angle for positive indication of position, resulting in a VOR/  VOR fix.  Landing Distance Available (LDA). ICAO defines LDA as the  length of runway, that is declared available and suitable for  the ground run of an aeroplane landing.  G-5  Head-Up Display (HUD). See head-up guidance system  (HGS).  Ground Communication Outlet (GCO). An unstaffed,  remotely controlled ground/ground communications  facility. Pilots at uncontrolled airports may contact ATC and  AFSS via very high frequency (VHF) radio to a telephone  connection. This lets pilots obtain an instrument clearance  or close a VFR/IFR flight plan.  Gross Navigation Error (GNE). In the North Atlantic area of  operations, a gross navigation error is a lateral separation  of more than 25 NM from the centerline of an aircraft’s  cleared route, which generates an Oceanic Navigation Error  Report. This report is also generated by a vertical separation  if you are more than 300 feet off your assigned flight level.  Global Navigation Satellite System (GNSS). An umbrella term  adopted by the International Civil Aviation Organization  (ICAO) to encompass any independent satellite navigation  system used by a pilot to perform onboard position  determinations from the satellite data.  Glidepath Angle (GPA). The angular displacement of the  vertical guidance path from a horizontal plane that passes  through the reference datum point (RDP). This angle is  published on approach charts (e.g., 3.00°, 3.20°, etc.). GPA  is sometimes referred to as vertical path angle (VPA).  Gateway Fix. A navigational aid or fix where an aircraft  transitions between the domestic route structure and the  oceanic route airspace.  Four Corner Post Configuration. An arrangement of air  traffic pathways in a terminal area that brings incoming  flights over fixes at four corners of the traffic area, while  outbound flights depart between the fixes, thus minimizing  conflicts between arriving and departing traffic.  Fly-over (FO) Waypoint. A waypoint that precludes any turn  until the waypoint is overflown, and is followed by either  an intercept maneuver of the next flight segment or direct  flight to the next waypoint.  Geodetic Datum. The reference plane from which geodetic  calculations are made. Or, according to ICAO Annex 15, the  numerical or geometrical quantity or set of such quantities  (mathematical model) that serves as a reference for  computing other quantities in a specific geographic region,  such as the latitude and longitude of a point.  International Civil Aviation Organization (ICAO). 