Aeronautical Terms beginning with H

Head-Up Display (HUD)

See Head-Up Guidance System (HGS)


Head-Up Guidance System (HGS)

A system which projects critical flight data on a display positioned between the pilot and the windscreen. In addition to showing primary flight information, the HUD computes an extremely accurate instrument approach and landing guidance solution, and displays the result as a guidance cue for head-up viewing by the pilot.


Height Above Touchdown (HAT)

The height of the DA above touchdown zone elevation (TDZE).


Highway in the Sky (HITS)

A graphically intuitive pilot interface system that provides an aircraft operator with all of the attitude and guidance inputs required to safely fly an aircraft in close conformance to air traffic procedures.


Hand Propping

Starting an engine by rotating the propeller by hand.


Heading

The direction in which the nose of the aircraft is pointing during flight.


Heading Bug

A marker on the heading indicator that can be rotated to a specific heading for reference purposes, or to command an autopilot to fly that heading.


Heading Indicator

An instrument which senses airplane movement and displays heading based on a 360º azimuth, with the final zero omitted. The heading indicator, also called a directional gyro, is fundamentally a mechanical instrument designed to facilitate the use of the magnetic compass. The heading indicator is not affected by the forces that make the magnetic compass difficult to interpret.


Headwind Component

The component of atmospheric winds that acts opposite to the aircraft’s flightpath.


High Performance Aircraft

An aircraft with an engine of more than 200 horsepower.


Horizon

The line of sight boundary between the earth and the sky.


Horsepower

The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.


Hot Start

In gas turbine engines, a start which occurs with normal engine rotation, but exhaust temperature exceeds prescribed limits. This is usually caused by an excessively rich mixture in the combustor. The fuel to the engine must be terminated immediately to prevent engine damage.


Hung Start

In gas turbine engines, a condition of normal light off but with r.p.m. remaining at some low value rather than increasing to the normal idle r.p.m. This is often the result of insufficient power to the engine from the starter. In the event of a hung start, the engine should be shut down.


Hydraulics

The branch of science that deals with the transmission of power by incompressible fluids under pressure.


Hydroplaning

A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning.


Hypoxia

A lack of sufficient oxygen reaching the body tissues.


Hazardous attitudes

Five aeronautical decision-making attitudes that may contribute to poor pilot judgment: antiauthority, impulsivity, invulnerability, machismo, and resignation.


Hazardous Inflight Weather Advisory Service (HIWAS).

Service providing recorded weather forecasts broadcast to airborne pilots over selected VORs. Discontinued on January 8, 2020.


Head-up display (HUD)

A special type of flight viewing screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the aircraft for other traffic, the approach lights, or the runway.


Height above airport (HAA)

The height of the MDA above the published airport elevation.


Height above landing (HAL)

The height above a designated helicopter landing area used for helicopter instrument approach procedures.


Height above touchdown elevation (HAT)

The DA/DH or MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway).


Holding

A predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC.


Holding pattern

A racetrack pattern, involving two turns and two legs, used to keep an aircraft within a prescribed airspace with respect to a geographic fix. A standard pattern uses right turns; nonstandard patterns use left turns.


Homing

Flying the aircraft on any heading required to keep the needle pointing to the 0 relative bearing position.


Horizontal situation indicator (HSI)

A flight navigation instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness of location with respect to the courseline.


Human factors

A multidisciplinary field encompassing the behavioral and social sciences, engineering, and physiology, to consider the variables that influence individual and crew performance for the purpose of optimizing human performance and reducing errors.


Hypoxia

A state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs.


Hierarchy of human needs

A listing by Abraham Maslow of needs, from the most basic to the most fulfilling: physiological, security, belonging, esteem, cognitive and aesthetic, and self-actualization.


Human factors

A multidisciplinary field devoted to optimizing human performance and reducing human error. It incorporates the methods and principles of the behavioral and social sciences, engineering, and physiology. It may be described as the applied science which studies people working together in concert with machines. Human factors involve variables that influence individual performance, as well as team or crew performance.


Human nature

The general psychological characteristics, feelings, and behavioral traits shared by all humans.


Helicopter

A rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.


Heliport

An area of land, water, or structure used or intended to be used for the landing and takeoff of helicopters.


Hail

A form of precipitation composed of balls or irregular lumps of ice, always produced by convective clouds which are nearly always cumulonimbus.


Halo

A prismatically colored or whitish circle or arcs of a circle with the sun or moon at its center; coloration, if not white, is from red inside to blue outside (opposite that of a corona); fixed in size with an angular diameter of 22° (common) or 46° (rare); characteristic of clouds composed of ice crystals; valuable in differentiating between cirriform and forms of lower clouds.


Haze

A type of lithometeor composed of fine dust or salt particles dispersed through a portion of the atmosphere; particles are so small they cannot be felt or individually seen with the naked eye (as compared with the larger particles of dust), but diminish the visibility; distinguished from fog by its bluish or yellowish tinge.


High

An area of high barometric pressure, with its attendant system of winds; an anticyclone. Also high pressure system.


Humidity

Water vapor content of the air; may be expressed as specific humidity, relative humidity, or mixing ratio.


Hurricane

A tropical cyclone in the Western Hemisphere with winds in excess of 65 knots or 120 km/h.


Hydrometeor

A general term for particles of liquid water or ice such as rain, fog, frost, etc., formed by modification of water vapor in the atmosphere; also water or ice particles lifted from the earth by the wind such as sea spray or blowing snow.


Hygrograph

The record produced by a continuous-recording hygrometer.


Hygrometer

An instrument for measuring the water vapor content of the air.


Hazardous attitudes

Five aeronautical decision-making attitudes that may contribute to poor pilot judgment: anti-authority, impulsivity, invulnerability, machismo, and resignation.


Hazardous Inflight Weather Advisory Service (HIWAS)

Service providing recorded weather forecasts broadcast to airborne pilots over selected VORs. Discontinued on January 8, 2020.


Head-up display (HUD)

A special type of flight viewing screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the aircraft for other traffic, the approach lights, or the runway.


Heading

The direction in which the nose of the aircraft is pointing during flight.


Heading indicator

An instrument which senses airplane movement and displays heading based on a 360° azimuth, with the final zero omitted. The heading indicator, also called a directional gyro (DG), is fundamentally a mechanical instrument designed to facilitate the use of the magnetic compass. The heading indicator is not affected by the forces that make the magnetic compass difficult to interpret.


Headwork

Required to accomplish a conscious, rational thought process when making decisions. Good decision-making involves risk identification and assessment, information processing, and problem solving.


Height above airport (HAA)

The height of the MDA above the published airport elevation.


Height above landing (HAL)

The height above a designated helicopter landing area used for helicopter instrument approach procedures.


Height above touchdown elevation (HAT)

The DA/DH or MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway).


High performance aircraft

An aircraft with an engine of more than 200 horsepower.


Histotoxic hypoxia

The inability of cells to effectively use oxygen. Plenty of oxygen is being transported to the cells that need it, but they are unable to use it.


Holding

A predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC.


Holding pattern

A racetrack pattern, involving two turns and two legs, used to keep an aircraft within a prescribed airspace with respect to a geographic fix. A standard pattern uses right turns; nonstandard patterns use left turns.


Homing

Flying the aircraft on any heading required to keep the needle pointing to the 0° relative bearing position.


Horizontal situation indicator (HSI)

A flight navigation instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness of location with respect to the courseline.


Horsepower

The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.


Hot start

In gas turbine engines, a start which occurs with normal engine rotation, but exhaust temperature exceeds prescribed limits. This is usually caused by an excessively rich mixture in the combustor. The fuel to the engine must be terminated immediately to prevent engine damage.


Human factors

A multidisciplinary field encompassing the behavioral and social sciences, engineering, and physiology, to consider the variables that influence individual and crew performance for the purpose of optimizing human performance and reducing errors.


Hung start

In gas turbine engines, a condition of normal light off but with rpm remaining at some low value rather than increasing to the normal idle rpm. This is often the result of insufficient power to the engine from the starter. In the event of a hung start, the engine should be shut down.


Hydroplaning

A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning.


Hypemic hypoxia

A type of hypoxia that is a result of oxygen deficiency in the blood, rather than a lack of inhaled oxygen. It can be caused by a variety of factors. Hypemic means “not enough blood.”.


Hyperventilation

Occurs when an individual is experiencing emotional stress, fright, or pain, and the breathing rate and depth increase, although the carbon dioxide level in the blood is already at a reduced level. The result is an excessive loss of carbon dioxide from the body, which can lead to unconsciousness due to the respiratory system’s overriding mechanism to regain control of breathing.


Hypoxia

A state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs.


Hypoxic hypoxia

This type of hypoxia is a result of insufficient oxygen available to the lungs. A decrease of oxygen molecules at sufficient pressure can lead to hypoxic hypoxia.


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