Glossary of Terms

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Gain-to-noise temperature ratio

Gain-to-noise temperature ratio. The ratio, usually expressed in dB/K, of the antenna gain to the noise at the receiver output
of the antenna subsystem. The noise is expressed as the temperature that a 1 ohm resistor must be raised to produce the
same noise power density.


GAMET area forecast. An area forecast in abbreviated plain language for low-level flights for a flight information region or
sub-area thereof, prepared by the meteorological office designated by the meteorological authority concerned and
exchanged with meteorological offices in adjacent flight information regions, as agreed between the meteorological
authorities concerned.


GBAS landing system (GLS) means an approach landing system using ground based augmented global navigation satellite system (GNSS/GBAS) information to provide guidance to the aircraft based on its lateral and vertical GNSS position. It uses geometric altitude reference for its final approach slope.

Geodesic distance

Geodesic distance. The shortest distance between any two points on a mathematically defined ellipsoidal surface.

Geodetic datum

Geodetic datum. A minimum set of parameters required to define location and orientation of the local reference system with
respect to the global reference system/frame.


Geoid. The equipotential surface in the gravity field of the Earth which coincides with the undisturbed mean sea level (MSL)
extended continuously through the continents.
Note.— The geoid is irregular in shape because of local gravitational disturbances (wind tides, salinity, current, etc.) and
the direction of gravity is perpendicular to the geoid at every point.

Geoid undulation

Geoid undulation. The distance of the geoid above (positive) or below (negative) the mathematical reference ellipsoid.
Note.— In respect to the World Geodetic System — 1984 (WGS-84) defined ellipsoid, the difference between the WGS-84
ellipsoidal height and orthometric height represents WGS-84 geoid undulation.

Glide path.

Glide path. A descent profile determined for vertical guidance during a final approach.


A non-power-driven heavier-than-air aircraft, deriving its lift in flight chiefly from aerodynamic reactions on surfaces
which remain fixed under given conditions of flight.

Glider flight time

The total time occupied in flight, whether being towed or not, from the moment the glider first moves for the
purpose of taking off until the moment it comes to rest at the end of the flight.

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