- 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
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.