Aeronautical Terms beginning with G

Gateway Fix

A navigational aid or fix where an aircraft transitions between the domestic route structure and the oceanic route airspace.


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.


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).


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.


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 aircrafts 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.


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.


Gas Generator

The basic power producing portion of a gas turbine engine and excluding such sections as the inlet duct, the fan section, free power turbines, and tailpipe. Each manufacturer designates what is included as the gas generator, but generally consists of the compressor, diffuser, combustor, and turbine.


Gas Turbine Engine

A form of heat engine in which burning fuel adds energy to compressed air and accelerates the air through the remainder of the engine. Some of the energy is extracted to turn the air compressor, and the remainder accelerates the air to produce thrust. Some of this energy can be converted into torque to drive a propeller or a system of rotors for a helicopter.


Glide Ratio

The ratio between distance traveled and altitude lost during non-powered flight.


Glidepath

The path of an aircraft relative to the ground while approaching a landing.


Global Position System (GPS)

A satellite-based radio positioning, navigation, and time-transfer system.


Go-Around

Terminating a landing approach.


Governing Range

The range of pitch a propeller governor can control during flight.


Governor

A control which limits the maximum rotational speed of a device.


Gross Weight

The total weight of a fully loaded aircraft including the fuel, oil, crew, passengers, and cargo.


Ground Adjustable Trim Tab

A metal trim tab on a control surface that is not adjustable in flight. Bent in one direction or another while on the ground to apply trim forces to the control surface.


Ground Effect

A condition of improved performance encountered when an airplane is operating very close to the ground. When an airplane’s wing is under the influence of ground effect, there is a reduction in upwash, downwash, and wingtip vortices. As a result of the reduced wingtip vortices, induced drag is reduced.


Ground Idle

Gas turbine engine speed usually 60-70 percent of the maximum r.p.m. range, used as a minimum thrust setting for ground operations.


Ground Loop

A sharp, uncontrolled change of direction of an airplane on the ground.


Ground Power Unit (GPU)

A type of small gas turbine whose purpose is to provide electrical power, and/or air pressure for starting aircraft engines. A ground unit is connected to the aircraft when needed. Similar to an aircraft-installed auxiliary power unit.


Ground Track

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


Groundspeed (GS)

The actual speed of the airplane over the ground. It is true airspeed adjusted for wind. Groundspeed decreases with a headwind, and increases with a tailwind.


Gust Penetration Speed

The speed that gives the greatest margin between the high and low mach speed buffets.


Gyroscopic Precession

An inherent quality of rotating bodies, which causes an applied force to be manifested 90º in the direction of rotation from the point where the force is applied.


Glide slope (GS)

Part of the ILS that projects a radio beam upward at an angle of approximately 3° from the approach end of an instrument runway. The glide slope provides vertical guidance to aircraft on the final approach course for the aircraft to follow when making an ILS approach along the localizer path.


Glide slope intercept altitude

The minimum altitude of an intermediate approach segment prescribed for a precision approach that ensures obstacle clearance.


Global landing system (GLS)

An instrument approach with lateral and vertical guidance with integrity limits (similar to barometric vertical navigation (BRO VNAV).


Global navigation satellite systems (GNSS)

Satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few meters using time signals transmitted along a line of sight by radio from satellites.


Global positioning system (GPS)

Navigation system that uses satellite rather than ground-based transmitters for location information.


Goniometer

As used in radio frequency (RF) antenna systems, a direction-sensing device consisting of two fixed loops of wire oriented 90 from each other, which separately sense received signal strength and send those signals to two rotors (also oriented 90) in the sealed direction-indicating instrument. The rotors are attached to the direction-indicating needle of the instrument and rotated by a small motor until minimum magnetic field is sensed near the rotors.


GPS Approach Overlay Program

An authorization for pilots to use GPS avionics under IFR for flying designated existing nonprecision instrument approach procedures, with the exception of LOC, LDA, and SDF procedures.


Graveyard spiral

The illusion of the cessation of a turn while still in a prolonged, coordinated, constant rate turn, which can lead a disoriented pilot to a loss of control of the aircraft.


Great circle route

The shortest distance across the surface of a sphere (the Earth) between two points on the surface.


Ground proximity warning system (GPWS)

A system designed to determine an aircrafts clearance above the Earth and provides limited predictability about aircraft position relative to rising terrain.


Groundspeed

Speed over the ground, either closing speed to the station or waypoint, or speed over the ground in whatever direction the aircraft is going at the moment, depending upon the navigation system used.


Goals and values

A perception factor that describes how a person’s perception of an event depends on beliefs. Motivation toward learning is affected by how much value a person puts on education. Instructors who have some idea of the goals and values of their students will be more successful in teaching them.


Guided discussion method

An educational presentation typically used in the classroom where the topic to be covered by a group is introduced and the instructor participates only as necessary to keep the group focused on the subject.


Glider

A heavier-than-air aircraft, that is supported in flight by the dynamic reaction of the air against its lifting surfaces and whose free flight does not depend principally on an engine.


Ground visibility

Prevailing horizontal visibility near the earth’s surface as reported by the United States National Weather Service or an accredited observer.


Go-around power or thrust setting

The maximum allowable in-flight power or thrust setting identified in the performance data.


Gyrodyne

A rotorcraft whose rotors are normally engine-driven for takeoff, hovering, and landing, and for forward flight through part of its speed range, and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system.


Gyroplane

A rotorcraft whose rotors are not engine-driven, except for initial starting, but are made to rotate by action of the air when the rotorcraft is moving; and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system.


Glaze

A coating of ice, generally clear and smooth, formed by freezing of super.cooled water on a surface.


Gradient

In meteorology, a horizontal decrease in value per unit distance of a parameter in the direction of maximum decrease; most commonly used with pressure, temperature, and moisture.


Ground clutter

Pertaining to radar, a cluster of echoes, generally at short range, reflected from ground targets.


Ground fog

In the United States, a fog that conceals less than 0.6 of the sky and is not contiguous with the base of clouds.


Gust

A sudden brief increase in wind; according to U.S. weather observing practice, gusts are reported when the variation in wind speed between peaks and lulls is at least 10 knots.


Gimbal ring

A type of support that allows an object, such as a gyroscope, to remain in an upright condition when its base is tilted.


Glideslope (GS)

Part of the ILS that projects a radio beam upward at an angle of approximately 3° from the approach end of an instrument runway. The glideslope provides vertical guidance to aircraft on the final approach course for the aircraft to follow when making an ILS approach along the localizer path.


Glideslope intercept altitude

The minimum altitude of an intermediate approach segment prescribed for a precision approach that ensures obstacle clearance.


Global landing system (GLS)

An instrument approach with lateral and vertical guidance with integrity limits (similar to barometric vertical navigation (BARO VNAV).


Global navigation satellite system (GNSS)

Satellite navigation system that provides autonomous geospatial positioning with global coverage. It allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few meters using time signals transmitted along a line of sight by radio from satellites.


Global positioning system (GPS)

Navigation system that uses satellite rather than ground-based transmitters for location information.


Goniometer

As used in radio frequency (RF) antenna systems, a direction-sensing device consisting of two fixed loops of wire oriented 90° from each other, which separately sense received signal strength and send those signals to two rotors (also oriented 90°) in the sealed direction-indicating instrument. The rotors are attached to the direction-indicating needle of the instrument and rotated by a small motor until minimum magnetic field is sensed near the rotors.


GPS Approach Overlay Program

An authorization for pilots to use GPS avionics under IFR for flying designated existing nonprecision instrument approach procedures, with the exception of LOC, LDA, and SDF procedures.


Graveyard spiral

The illusion of the cessation of a turn while still in a prolonged, coordinated, constant rate turn, which can lead a disoriented pilot to a loss of control of the aircraft.


Great circle route

The shortest distance across the surface of a sphere (the Earth) between two points on the surface.


Ground adjustable trim tab

Non-movable metal trim tab on a control surface. Bent in one direction or another while on the ground to apply trim forces to the control surface.


Ground effect

The condition of slightly increased air pressure below an airplane wing or helicopter rotor system that increases the amount of lift produced. It exists within approximately one wing span or one rotor diameter from the ground. It results from a reduction in upwash, downwash, and wingtip vortices, and provides a corresponding decrease in induced drag.


Ground proximity warning system (GPWS)

A system designed to determine an aircraft’s clearance above the Earth and provides limited predictability about aircraft position relative to rising terrain.


Groundspeed

Speed over the ground, either closing speed to the station or waypoint, or speed over the ground in whatever direction the aircraft is going at the moment, depending upon the navigation system used.


Gyroscopic precession

An inherent quality of rotating bodies, which causes an applied force to be manifested 90° in the direction of rotation from the point where the force is applied.


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