Aeronautical Terms beginning with G

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.


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.


Terminating a landing approach.

Governing Range

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


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.

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