GPWS ground proximity warning system. A radar-based flight- deck system to give pilots audible warning by means of horns, hooters, taped or synthetic voices of terrain close beneath an aircraft's flight path.
GRADU gradual (term used in Met reports).
GRP glassfibre-reinforced plastic; also CFRP, carbon-fibre reinforced plastic. Composite materials seeing increasing use in entire airframes for GA aircraft (e.g. Beech Starship) and for components for helicopters, airliners and military aircraft.
GS glideslope. The vertical guidance part of an instrument landing system which establishes a safe glidepath (usually three degrees) to a runway.
G/S groundspeed. The speed an aircraft makes over the ground, a product of its airspeed and wind speed.
H24 continuous round-the-clock operation. Also HJ operates during day; HN operates during night; HO operates during times to meet operational requirements, and HX no specific operational hours.
HAA Historic Aircraft Association
HAI Helicopter Association International
half-mill(ion) 1:500,000 scale ICAO aeronautical chart
Hdg heading. The direction in which an aircraft's nose points in flight in the horizontal plane, expressed in compass degrees.
Heavy suffix used in RT callsigns to indicate that the aircraft is a large transport, alerting controllers and following aircraft to the possibility of wake turbulence .
Hectopascal (hPa) unit of pressure measurement, equivalent to one millibar (which see), now the ICAO-standard for altimeter setting.
HEMS helicopter emergency medical services.
Hertz standard radio equivalent of frequency in cycles per second. See also kHz and MHz.
HF high-frequency band, used for long-range radio communications in the 3-30 MHz range.
Hg inches of mercury, a unit of pressure measurement.
HIAL high intensity approach lighting.
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