Aviation Glossary - H

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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 call-signs to indicate that the aircraft is a large transport, alerting controllers and following aircraft to the possibility of wake turbulence (which see).

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.

HIGE - hover in ground effect. Also see HOGE.

HIRF - high intensity radiated (electromagnetic) fields.

HIRL - high intensity runway lighting.

HISL - high intensity strobe light.

HOCAC - hands on cyclic and collective see HOTAS below.

HOGE - hover out of ground effect. Also see HIGE.

holding pattern - racetrack shaped manoeuvre which keeps aircraft within a specified airspace while awaiting further clearance from air traffic control.

HOTAS - hands on throttle and stick. Ergonomic cockpit design technology, originally developed for military combat aircraft, enabling a pilot to fly the aircraft and manage all navigation, weapons and other systems from control column/throttle lever hand grips.

HOTCC - hands on throttle, collective & cyclic see HOTAS above.

hp - horsepower.

HRA - Highlands Restricted Area

HSD - horizontal situation display.

HSI - horizontal situation indicator. A cockpit navigation display, usually part of a flight director system, which combines navigation and heading.

HUD - head up display. A method of projecting instrument readouts or data which enables a pilot to see them while looking through the aircraft's windscreen. Mostly used on military aircraft, but now in service on some commercial airliners.

Hz - Hertz.