Alpha
Bismillah
Charlie Delta
Echo
Foxtrot
Golf
Hotel
insaallah Juliett Kilo
Lima Mike November Oscar
Piaggio Quebec Romeo
Sierra Turks Uniform
Victory Water X-ray
Yankee Zulu Main Page
hacksaw
A hand-operated metal cutting saw with narrow, replaceable blades. The replaceable blade is held in the hacksaw frame under tension.hailstones Precipitation formed by drops of water carried by upward currents of wind inside a cumulonimbus cloud to a level where the temperature is low enough to freeze the drops into ice. When the hailstones are too heavy to be carried in the cloud, they fall to the ground.
hairline A very thin line.
hairline crack A nearly imperceptible crack on the surface of a piece of material.
hairspring A flat, coiled spring used in aircraft instruments as either a calibrated restraint or a preloading device for the gears.
halation A distortion on a cathode-ray tube that shows up as a blurred area around an image.
half hitch A knot used for lacing wire bundles.
half life One half-life is the measure of the time a particular radioactive material loses one half of its radioactivity. At each half-life interval, the material loses one half more of its remaining life and so on.
half view An aircraft drawing that shows only one-half of a symmetrical view. Center lines and break lines are used to show that there is more of the object than is shown in the drawing.
half-duplex communication Communication in which signals can be sent in one direction at a time, but cannot be sent in both directions at the same time.
half-life inspection A jet engine inspection required under conditions of warranty, completed at half the time between overhaul (TBO) interval. It includes primarily a hot section disassembly, inspection, and repair as necessary.
half-round file A hand file that is flat on one side and curved on the other.
half-section A view in which the cutting plane extends only halfway across the object, leaving the other half of the object as an exterior view.
half-wave radio antenna An antenna with an electrical length that is approximately one half of the wavelength of the frequency for which the antenna is tuned.
half-wave rectifier A rectifier that changes AC into pulsating DC using one diode and producing only one half of the AC wave in its output.
Hall-effect generator An electronic device used to measure the intensity of a magnetic field. Converts magnetic field to a low-level electrical signal.
halo A circle of light that appears around the moon when seen through a thin layer of cirrostratus clouds. The halo appearance is caused by tiny ice crystals in the cloud that scatter the light passing through it.
halogen One of the five chemical elements (fluorine, chlorine, bromine, iodine, and astatine) in Group VII of the periodic table of chemical elements. Used in some fire extinguishing systems.
Halon Low-toxicity, chemically stable compounds used in fire protection systems. In aviation, Halon 1301 is most commonly used. The benefit of using Halon fire extinguishers is that they do not leave liquid or solid residues when discharged; therefore, they are preferred for sensitive areas and can be used in the presence of humans, which is important in closed areas. Halons are being phased out since they are a chlorofluorocarbon (CFC) and damage the ozone layer.
hammer A hand-tool consisting of a heavy head and a handle. It is used for pounding, driving, or shaping.
hammer welding A forge welding in which the edges of two pieces of metal are heated red-hot and then fused by beating with a hammer.
hand drill A hand-operated, eggbeater-type tool used to turn a twist drill.
hand driving A method of forming rivets in which the head is driven with a hand set and hammer, and the shank is bucked with a bucking bar.
hand file A hand-operated cutting tool made of high-carbon steel and fitted with rows of very shallow teeth extending diagonally across the width of the tool.
hand forming The process of shrinking, stretching, or forming sheet metal by using soft-faced mallets or hammers to force the metal down against suitable forming blocks or into dies.
hand inertia starter An inertia starter for reciprocating engines in which the flywheel is brought up to speed by a hand-operated crank.
hand lay-up In composites, assembling layers of reinforcement by hand. This includes the working the resin into the fabric, as well as using a pre-preg fabric.
hand pump A pump operated by hand to create a flow of fluid.
hand rivet set A rivet set that can be clamped into a vise to hold the manufactured head of the rivet while the shank is upset with a hammer and a flat punch.
hand snips Compound-action hand shears used for cutting sheet metal. They normally come in sets of three: one that cuts to the left, one that cuts to the right, and one that cuts straight.
hand tools A general name for all of the hand-operated tools used in the performance of maintenance.
hand-bending tools A hand-operated, tube-bending tool consisting of a clamp, a radius block, and a sliding bar. It is used to bend thin-wall aluminum alloy or copper tubing in such a way that it does not collapse the tube.
handbook A manual that describes simple operations or a system of operations. A handbook normally does not contain specific detailed information on the maintenance of such systems.
hand-cranked inertia starter A starter that uses a hand crank to store energy in a spinning flywheel. The crank is geared to the flywheel through a high-ratio gear system so that the flywheel can be spun at a high speed. The flywheel is coupled by a clutch to the crankshaft of the engine for starting.
handoff An action taken to transfer the radar identification of an aircraft from one controller to another if the aircraft will enter the receiving controller s airspace and radio communications with the aircraft will be transferred.
hangar A building used for the purpose of housing and maintaining aircraft.
hangar queen Slang, for an aircraft that is frequently non-airworthy and spends a lot of time in the hangar. In the military or commercial aviation, these aircraft are frequently robbed of parts to keep other aircraft airworthy, thus prolonging the status of the hangar queen. Also referred to as an orphaned airplane.
hard The condition of a material when it is compact, solid, and difficult to bend or deform.
hard landing An improper landing of an aircraft that has transmitted undue stresses into the structure. The degree of a landing s hardness determines the type of special inspection that will be performed to determine if there is structural damage to the aircraft.
hard X-rays The degree of the penetration power of an X-ray as determined by the amount of voltage that is applied to the anode of the X-ray tube. The higher the voltage, the greater its penetrating power.
hardboard A wood composition material manufactured by bonding sawdust and chips of wood with an adhesive under heat and pressure.
hard-drawn copper wire Copper wire that has been pulled through dies to reduce its diameter to a predetermined size. Pulling the wire also hardens the wire and increases its tensile strength.
hardenability In a ferrous alloy, the property of metal that determines the depth and distribution of hardness induced by heat treatment and quenching or by cold working.
hardened steel Steel that has been hardened by a process of heating the steel above its critical temperature then quenching it in brine, water, or oil. Although the hardened steel is very strong, it is also brittle.
hardener A chemical constituent of an adhesive that promotes its setting and hardening.
hardening 1. A heat treatment of metal that increases its brittleness as well as its resistance to abrasion while it decreases its ductility and malleability. 2. Aluminum: The process of increasing the strength and hardness of aluminum after it has been solution-heat treated. Age hardening takes several days at room temperature until the metal reaches its full hard state. 3. Steel: A process whereby steel is made hard and brittle by heating it to a temperature above its critical temperature and immediately quenching it in water or oil.
hard-facing A process of welding, plating, or spraying a hard material such as carbide on the surface of a tool to increase its hardness and to keep the tool from wearing.
hardness The property of a metal that enables it to resist penetration, wear, or cutting actions.
hardness test An evaluation of the hardness of a material by measuring the depth of penetration of a specially shaped probe under a specified load. The surface hardness of aluminum alloy parts such as brake housings and wheels can be measured to determine whether or not their heat treatment has been affected by overheating.
hardware The nuts, bolts, screws, rivets, etc. necessary for assembling parts.
hardwood A wood with compact texture.
harmonic A frequency of vibration that is an even multiple of the fundamental of another vibration frequency.
harness satin A weaving pattern producing a satin appearance. See also eight-harness satin and four-harness satin.
Hartley oscillator An electronic oscillator that produces its feedback through a tapped inductor.
have numbers Used by pilots to inform ATC that they have received runway, wind, and altimeter information only.
hazardous attitudes Studies have identified five hazardous attitudes that can interfere with a pilot s ability to make sound decisions and exercise authority properly. The five hazardous attitudes are anti-authority, impulsivity, invulnerability, macho, and resignation.
hazardous inflight weather advisory service (HIWAS) Continuous recorded hazardous inflight weather forecasts broadcasted to airborne pilots over selected VOR outlets defined as an HIWAS Broadcast Area.
hazardous weather information Summary of significant meteorological information (SIGMET/ WS), convective significant meteorological information, (convective SIGMET/WST), urgent pilot weather reports (urgent PIREP/UUA), center weather advisories (CWA), airmen s meteorological information (AIRMET/WA) and any other weather such as isolated thunderstorms that are rapidly developing and increasing in intensity, or low ceilings and visibilities that are becoming widespread which is considered significant and are not included in a current hazardous weather advisory.
haze 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 large particle of dust), but diminish the visibility; distinguished from fog by its bluish or yellowish tinge.
heading The direction in which the longitudinal axis of the airplane points with respect to true or magnetic north. Heading is equal to course plus or minus any wind correction angle.
heads up display (HUD) A system that displays flight information on a transparent display in the line-of-sight of the pilot so that information can be read without looking down into the cockpit. Newest terminology is Head-up Guidance System (HGS).
head-up guidance system (HGS) See heads up display.
headwind component That portion of the wind which acts straight down the runway toward the airplane on takeoff or parallel to the line of flight when airborne.
headwork Conscious, rational thought process when making decisions.
heat Energy associated with the motion of molecules within a material. The more heat energy there is in a material, the faster its molecules move.
heat capacity The amount of heat energy required to raise the temperature of a substance 1 C.
heat dissipation The loss of heat or the transfer of heat into another object or substance.
heat energy Energy associated with the motion of the molecules within a substance.
heat engine Any mechanical device that converts heat energy into mechanical energy. For example, reciprocating and turbine engines are heat engines.
heat exchanger Any device used to transfer heat from one body to another.
heat lamp An incandescent lamp that produces a maximum of infrared radiation with a minimum of visible light rays. Used for drying paint or for applying heat to glued parts to decrease curing time.
heat load The amount of heat that an air conditioner is required to remove from an airplane cabin in order to maintain a constant cabin temperature.
heat of compression The heat generated when a gas is compressed.
heat pump Moves heat from one location to another. A heat pump can generally be reversed so that it either adds heat (acts as a heater) or takes heat away (acts as an air conditioner).
heat sink 1. A device on which semiconductors can be mounted to absorb the heat that would normally tend to damage them. 2. A heavy plate of conductive material that will absorb or carry away heat. Especially useful in welding.
heat treatment of a plastic resin The operation in which a cemented joint in a thermoplastic resin is held at an elevated temperature so the entrapped solvent can diffuse into a greater volume of the resin. This decreases its concentration and increases the strength of the joint.
heat treatment of metals Any operation in which the physical characteristics of a metal are changed by heating. This includes annealing, hardening, tempering, and normalizing.
heat value The heat energy available per unit volume of a fuel.
heater Any device that produces controlled heating.
heating element An electrical resistance wire that glows red-hot to produce heat.
heat-shrinkable A quality in a synthetic fiber that allows a fabric to shrink when heat is applied.
heatshrinkable fabric An inorganic fabric used to cover light aircraft structures. The fabric is sewn and put on the aircraft structure so that it is taut but not tight. After securing the fabric to the structure with a special adhesive, it is shrunk to the correct tautness by ironing it with an ordinary household electric iron or by heating it with a high wattage hair dryer. The material is then given a coating of non-tautening dope.
Heaviside atmospheric layer A layer of ionized particles that surrounds the Earth. The ionosphere.
heavy (aircraft) For the purposes of Wake Turbulence Separation Minima, ATC classifies aircraft as Heavy, Large, and Small. Heavy aircraft are capable of takeoff weights of more than 255,000 pounds whether or not they are operating at this weight during any particular phase of flight. See Aircraft Classes
heavy ends In the fractional distillation process, the last parts of crude petroleum refining that have the highest boiling points.
heavy snow warning A warning that snowfall may exceed four inches or more in a 12-hour period or six inches in a 24-hour period.
Hecto One hundred.
hedge-hopping An aircraft flying very near the Earth s surface yet avoiding obstructions on the ground.
height above airport (HAA) The height of the Minimum Descent Altitude (MDA) above the published airport elevation. This is published in conjunction with circling minimums.
height above landing The height above a designated helicopter landing area used for helicopter instrument approach procedures.
height above touchdown (HAT) The height of the Decision Height or Minimum Descent Altitude above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway). HAT is published on instrument approach charts in conjunction with all straight-in minimums.
height band In gliders, the altitude range in which the thermals are strongest on any given day. Remaining with the height band on a cross-country flight should allow the fastest average speed.
height gradient The rate of change of height per unit of distance on a constant pressure chart.
Heliarc A welding process used extensively on aircraft parts. It is a gas-shielded process to prevent oxidation of the base metal. The two types of Heliarc welding are tungsten inert-gas (TIG) welding and metal inert-gas (MIG) welding.
helical A line or form that winds around a cylinder or the line of threads on a bolt.
helical potentiometer A potentiometer with a resistance element made in the form of a spiral. The wiper is moved over the element by turning a multi-turn screw.
helical spline A spline that winds around a shaft. Helical splines are used to change the linear motion of the device that rides on the splines into the shaft s rotary motion on which the splines are cut.
helical spring A spring wound in the form of a spiral.
Helicoil A special helical steel insert screwed into specially cut threads to restore threads that have been stripped out or to provide durable threads in soft castings.
helicopter A rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.
helipad A small, designated area, usually with a prepared surface, on a heliport, airport, landing/ takeoff area, apron/ramp, or movement area used for takeoff, landing, or parking of helicopters.
heliport An area of land, water, or structure used or intended to be used for the landing and takeoff of helicopters and includes its buildings and facilities, if any.
heliport reference point (HRP) The geographic center of a heliport.
helium An inert, gaseous, chemical element with a symbol of He and an atomic number of 2. Used to inflate lighter-than-air aircraft.
henry The standard unit of inductance. It is the amount of inductance in which a current change of one ampere per second will induce a voltage of one volt. Named for Joseph Henry, an American physicist.
heptane A liquid hydrocarbon material (C7H17) having a low critical pressure and temperature and whose detonation characteristics are used in determining the octane rating of aviation gasoline.
heptode A vacuum tube that has seven active electrodes, including the anode, cathode, control grid, and four other special-purpose grids such as screen grids, suppressor grids, and beam-forming grids.
hermaphrodite calipers A tool used to scribe lines equidistant from an edge. Consists of a caliper with one pointed leg and one with a hook on the end as with an outside caliper. The hook is placed on the edge of the material, and the point is used to scribe a line.
hermetically sealed A method of protecting an aircraft instrument by exhausting all of the air from its case and sealing it so that no moisture can get in.
hermetically sealed integrating gyro (HIG) A gyro mounted in a sealed case with a viscous damping medium. The output is therefore an indication of the total amount of angular displacement of the vehicle in which the gyro is installed rather than the rate of angular displacement.
Hertz antenna A half-wave radio antenna.
hertz (Hz) A unit used for measuring the frequency of vibrations or of AC electricity. It is used for the frequency of any type of repeating cycles of motion. One hertz is equal to one cycle per second. Named for Heinrich Hertz, a German physicist.
heterodyne To mix or beat together two frequencies in order to produce an intermediate frequency.
heterodyne-type frequency meter A frequency meter that beats (heterodynes) an unknown-frequency signal against a locally-produced signal from a variable-frequency generator. When the beat is of zero frequency, the frequency of the incoming signal can be read from a dial or a digital display showing the frequency of the local generator.
heterogeneous mixture A mixture composed of dissimilar ingredients.
hexadecimal number system A number system that uses the base 16. (The decimal system uses the base ten).
hexagon A figure that has six sides.
hexagon head bolt A bolt head shaped with six sides (a hexagon).
hexode An electron tube having six active elements.
HF communications See high frequency communications.
hidden surfaces Any surface represented on an aircraft drawing that cannot be seen in a particular view but is represented in outline form with hidden lines.
hierarchy of human needs A listing by Abraham Maslow of needs from the most basic to the most fulfilling. These range from physical through safety, social, and ego to self-fulfillment.
high An area of high barometric pressure, with its attendant system of winds; an anticyclone. Also referred to as a high-pressure system.
high altitude checkout FAR 61.31(f) requires specific ground and flight training for a pilot to act as PIC of a pressurized airplane that has a service ceiling or maximum operating altitude, whichever is lower, above 25,000 MSL. High-altitude checkouts require both ground and flight training. Included in the ground training is a thorough review of the physiological aspects of high-altitude flight. An overview of these effects is contained in Chapter 8 of the Aeronautical Information Manual (AIM) and AC 61-107, Operations of Aircraft at Altitudes Above 25,000 Feet MSL and/or MACH Numbers (Mmo) Greater Than .75. AC 61-107 contains a recommended outline for a high-altitude training program. An instructor needs a logbook endorsement for high-altitude operations to give flight instruction in a pressurized airplane that has a service ceiling or maximum operating altitude above 25,000 feet MSL.
high blower The high-speed operation of a single-stage, two -speed, internal supercharger system. Usually about 10:1 ratio.
high cycle fatigue A condition seen as cracking or stretching caused by vibration stresses above the design limit of the engine.
high frequency The frequency band between 3 and 30 MHz.
high frequency communications High radio frequencies (HF) between 3 and 30 MHz used for air-to-ground voice communication in overseas operations.
high performance airplane An airplane with an engine of more than 200 horsepower.
high pressure turbine In gas turbine engines, the turbine rotor which drives the high pressure compressor in a dual or triple spool axial flow gas turbine engine.
high speed exit See high speed taxiway.
high speed taxiway A long radius taxiway designed and provided with lighting or marking to define the path of aircraft, traveling at high speed (up to 60 knots), from the runway center to a point on the center of a taxiway. Also referred to as long radius exit or turn-off taxiway. The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.
high speed taxiway / turnoff (HST) A long radius taxiway designed and provided with lighting or marking to define the path of an aircraft, traveling at high speed (up to 60 knots), from the runway center to a point on the center of a taxiway. Also referred to as long radius exit or turnoff taxiway. The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.
high speed turnoff See high speed taxiway.
high strength steel Steel that has a tensile strength of between 50,000 and 100,000 PSI.
high-bypass turbofan Turbine engines with 4:1 fan-to-engine bypass ratio or higher. That is, four or more times as much air flows through the fan as through the core engine.
high-bypass turbofan engine A turbofan engine in which the mass airflow in pounds per second that passes through the fan can be four times or more greater than that which is moved by the gas generator or core of the engine.
high-carbon steel Steel that contains more than 0.5% carbon.
high-frequency communications Radio communication at a frequency that is above the upper end of the commercial AM broadcasting band.
high-level language The language of computer instruction a computer can understand.
high-lift device Any lift-modifying device such as a slot, slat, or any of the forms of flaps that are used to allow an airfoil to achieve a higher angle of attack before airflow separation occurs.
high-pass filter An electronic filter that allows AC, above a certain frequency, to pass with little or no opposition.
high-potential ignition lead test A test performed on the spark plug electrical wires of an aircraft ignition system to see if there is a voltage leak to ground.
high-pressure compressor The rear section of a dual-spool compressor. Also referred to as an N2 compressor or high speed compressor.
high-pressure oxygen system Gaseous oxygen systems whose cylinders carry between 1,000 and 2,000 PSI pressure.
high-pressure system In gaseous systems, maximum pressure between 1,000 and 2,000 PSI. In liquid systems, it refers to approximately 300 PSI pressures.
high-pressure turbine The forward most turbine wheels, also called the N2 turbine or high-speed turbine, that drive the high-speed compressor in a two-spool, axial-flow gas turbine engine.
high-rate discharge See cold-cranking amps.
high-resistance connection An electrical connection with excessive resistance. Usually caused by a poor solder joint or loose fastener.
high-speed steel Alloys of steel that maintain their strength when operating at red-hot temperatures. They are used for metal-cutting tools.
high-speed taxiway exit or turnoff A wide radius turn-off from the runway to allow an aircraft to turn off at a higher rate of speed than would be possible on a normal right angle turn-off.
high-strength fastener A fastener with high tensile and shear strengths attained through combinations of materials, work-hardening, and heat treatment.
high-tension magneto A self-contained magneto ignition system used to provide a high potential voltage to the spark plugs. The magneto consists of a rotating magnet, cam, breaker points, capacitor, and a coil with a primary and a secondary winding. The output of the secondary winding goes to a distributor, then to the spark plugs.
high-voltage igniter plug An igniter plug utilizing an air gap between its center electrode and its outer casing. Used to start the engine combustion process.
high-voltage ignition system A main system with a voltage output in the range of approximately 5,000 to 30,000 volts delivered to the igniter plug.
high-wing airplane A monoplane with a single airfoil mounted on top of the fuselage.
hinge A fastener that allows one of the connected pieces to pivot with respect to the other.
hinge point The pivot point about which a control surface or a door hinges.
Hipernik A magnetic alloy made of 50% iron and 50% nickel.
Hi-Shear rivet A threadless bolt used for high-speed, high-strength, lightweight construction of an aircraft. A steel pin is held into the structure by an aluminum or mild-steel collar swaged into a groove around the end of the pin.
HIWAS area Hazardous Inflight Weather Advisory Service. Continuous recorded hazardous inflight weather forecasts broadcasted to airborne pilots over selected VOR outlets defined as an HIWAS Broadcast Area.
HIWAS broadcast area A geographical area of responsibility including one or more HIWAS outlet areas assigned to an AFSS/FSS for hazardous weather advisory broadcasting.
HIWAS outlet area An area defined as a 150 NM radius of a HIWAS outlet, expanded as necessary to provide coverage.
hold for release Used by ATC to delay an aircraft for traffic management reasons; i.e., weather, traffic volume, etc. Hold for release instructions (including departure delay information) are used to inform a pilot or a controller (either directly or through an authorized relay) that an IFR departure clearance is not valid until a release time or additional instructions have been received.
hold procedure A predetermined maneuver which keeps aircraft within a specified airspace while awaiting further clearance from air traffic control. Also used during ground operations to keep aircraft within a specified area or at a specified point while awaiting further clearance from air traffic control.
hold/holding procedure A pre-determined maneuver which keeps aircraft within a specified airspace while awaiting further clearance from air traffic control. Also used during ground operations to keep aircraft within a specified area or at a specified point while awaiting further clearance from air traffic control.
holding coil An auxiliary coil in an electrical relay that keeps the relay energized after the current that caused the relay to close has stopped flowing through the main coil.
holding fix A specified fix identifiable to a pilot by NAVAIDs or visual reference to the ground used as a reference point in establishing and maintaining the position of an aircraft while holding.
holding point [ICAO] A specified location, identified by visual or other means, in the vicinity of which the position of an aircraft in flight is maintained in accordance with air traffic control clearances
holding procedure An aircraft maneuver in which a pilot is instructed by air traffic control to maintain a specified air space until given further instruction.
hold-short point A point on the runway beyond which a landing aircraft with a LAHSO clearance is not authorized to proceed. This point may be located prior to an intersecting runway, taxi-way, predetermined point, or approach/departure flight path.
hold-short position lights Flashing in-pavement white lights located at specified hold-short points.
hold-short position marking The painted runway marking located at the hold-short point on all LAHSO runways.
hold-short position signs Red and White holding position signs located alongside the hold-short point.
hole 1. The vacancy in the valence structure of an element that will accept an electron from an outside source. 2. The absence of an electron at a point where one might be expected. For most purposes, a hole may be treated as a positive charge. 3. A serious discrepancy, flaw, or weakness. 4. An opening in which something is missing.
hole finder A tool used in sheet metal work to determine the rivet hole locations to be drilled in a piece of sheet metal so they will match those in the piece of metal being overlapped.
hole punch A hollow punch resembling a sharp-edged tube. It is used to punch holes in gasket material.
holist A learning style that focuses on the overall object first and then examines the individual components, using a top to bottom approach.
hollow drill A drill with a hole through its center making it easier for the drill to be lubricated.
hollow-mill collar cutter A tool used to remove collar material from pin rivets so the rivet can be tapped out of the work.
home study course Under FAR 61.35, a home study course may be used to meet the prerequisites for a knowledge test. Home study curriculums may be developed individually by students from material described in the applicable FAA knowledge test guide. Usually, home study courses are designed by pilot schools, colleges and universities, aviation organizations, publishers, or individual ground or flight instructors. The home study course may feature printed material, video, or computer-based training provided on CDs or accessed over the Internet. Regardless of the medium, students must show that the course has been satisfactorily completed and obtain an endorsement from an authorized instructor. Refer to Certification: Pilots and Flight Instructors (AC 61-65), which describes several methods that students can use to show evidence of having satisfactorily completed home study courses.
homebuilt airplane An aircraft constructed by an amateur builder. Such builders buy kits and/or plans for the aircraft and assemble the airplane over a period of years in their hangars, garages, and even basements. These airplanes are known as homebuilts. An airplane is considered amateur built if the builder constructs at least 51% of the aircraft. Manufacturers of homebuilt kits may not construct more than 49% of the total airplane.
homing A method of navigating to an NDB by holding a zero relative bearing. The result of homing in a crosswind is a curved course.
hone A fine abrasive stone used to sharpen cutting tools or create a finished surface.
honeycomb A material made up of hexagonal-shaped cells. Constructed of thin metal, paper, or plastic and used as a core material for sandwich structures. Named after a bee s honeycomb because of its appearance.
honeycomb shroud ring Honeycomb material into which a rotating airfoil can cut without degrading its air-sealing function. Usually in the hot section. Also referred to as an abradable shroud.
honing The process of removing a very small amount of material to produce a smooth finish on a surface or to produce a sharp edge on a cutting tool such as a knife or a chisel.
hook rule A steel scale with a hook or projection on one end so the rule can be used to measure accurately from the edge of materials.
hook spanner A semicircular spanner wrench with the handle on one end and a hook on the other. The hook engages notches in the outside circumference of a ring-type nut.
Hooke s law A law of physics that deals with the relationship between stress and strain in a material. It states that stress in a ductile material is directly proportional to the strain until the limit of elasticity of the material is reached.
hopper A funnel-shaped container used for storing the abrasive in a sand-blasting machine. The container has an opening in the top for loading and a smaller opening in the bottom for dumping.
hopper-type oil tank A container within an oil tank used to hold oil diluted with gasoline for cold weather starting. The use of a hopper minimizes the amount of oil that must be diluted.
horizon The line of sight boundary between the Earth and the sky.
horizontal Parallel to the Earth s horizon or to the base line of an object.
horizontal needle of the cross-point indicator The glide slope indicator of the standard ILS indicator (cross point indicator). The horizontal bar is also referred to the horizontal needle and indicates the position of the aircraft on the ILS glideslope.
horizontal pressure gradient force The force that arises because of a horizontal pressure gradient.
horizontal stabilizer A fixed horizontal airfoil attached to the rear of the fuselage to provide stability in pitch.
horizontal wind shear The change in wind direction and/or speed over a horizontal distance.
horizontally opposed engine A reciprocating engine with the cylinders arranged in two horizontal rows, one on either side of the crankshaft. The cylinders are slightly staggered, with the cylinders in one bank slightly ahead of those in the other bank. Staggering the cylinders allows each piston to be connected to a separate throw of the crankshaft.
horn A lever or device fastened or connected to a control surface to which an operating cable or rod is attached.
horse latitudes Approximately 30 to 35 north and south latitudes. An area of high barometric pressure and light, changeable winds.
horsepower (HP) The standard unit of power used for mechanical measurement. It is equal to 33,000 ft.-lbs. of work done in one minute, or 550 ft.-lbs. of work done in one second. Electrically, it is equal to 746 watts.
horseshoe magnet A magnet shaped like the letter U (or a horseshoe).
hose A flexible plumbing line used in place of rigid tubing in areas subject to movement or vibration.
hose clamp A metal clamp used to hold a rubber hose onto a piece of rigid tubing.
hot air muff A jacket installed around a tail pipe. Air routed through the hot air muff picks up heat by convection through the tail pipe material. This heated air is then routed to the cabin.
hot bond repair In composites, a repair made using a hot patch bonding machine to cure and monitor the curing operation. Hot bonding equipment typically includes both the heat source and the vacuum source.
hot corrosion Corrosion occurring in hot sections from a chemical reaction between sulfur in the fuel and salt in the air stream. This condition is more of a problem when operating near salt water.
hot dimpling A coin dimpling or countersinking of metal for flush rivets or screws. A heating unit heats the metals to prevent cracking around the hole.
hot forming Working operations such as bending and drawing sheet and plate, forging, pressing, and heading, performed on metal heated to temperatures above room temperature.
hot junction One end of a thermocouple. When combined with a cold junction, a small current is generated. The same principle is used in many fire detection systems. The cold junction is sometimes referred to as the reference junction.
hot section The portion of a turbine engine aft of the diffuser where combustion takes place.
hot section distress Any of the metal deterioration conditions found in the hot section such as warping or creeping.
hot section inspection An inspection of the hot section of a gas turbine engine.
hot shearing A method of cutting heavy sheets of magnesium alloys in which the metal is cut while hot. This improves the smoothness of the cut.
hot spark plug A spark plug with a long-nose insulator in which the heat transferring from the center electrode into the shell has a long path to travel. Hot spark plugs are used in engines that operate relatively cool, and they keep the center insulator hot enough to prevent the accumulation of lead oxides.
hot sparks Localized areas in the cylinder of an internal combustion engine that are overheated to the point where they become incandescent or glow. They cause pre-ignition.
hot spots Localized discoloration on hot section parts indicating a breakdown of cooling air or harmful concentration of fuel at that point. This often is the result of a malfunctioning fuel nozzle.
hot stamping A method of identifying or imprinting plastic materials, cloth, or paper by using heated metal dies.
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.
hot streak ignition An afterburner ignition system in which a stream of raw fuel continues to burn while passing through the turbine section and provides ignition for afterburner fuel supply.
hot valve clearance The clearance between the valve stem and the rocker arm when all of the engine parts have reached their operating temperature.
hot wire A wire connected directly to the power source.
hot-tank lubrication system A gas turbine engine lubrication system in which hot oil returns directly from the engine to the tank without being cooled because the oil cooler is in the pressure portion of the lubrication system.
hot-tank oil system A lubrication system where the oil cooler is located in the pressure oil subsystem and the scavenge oil returns to the oil tank uncooled.
hot-wire ammeter A current measuring instrument for measuring high frequency alternating current. The ammeter uses the heating effect of the high frequency current to heat a wire and change its length. As the wire lengthens, it moves a pointer across a dial to show the amount of current flowing through the wire.
hot-wire anemometer A wind speed indicator that measures the amount of heat the wind removes from a heated wire. The speed of the wind is proportional to the amount of heat removed.
hourmeter An odometer-type instrument used to measure hours of operating time. When incorporated into a mechanical tachometer, it is accurate only at a specified RPM.
housing A frame, box or casing that contains a part or mechanism.
hover The action of a helicopter maintaining a constant position over a selected point. Hovering allows the helicopter to sustain flight with no movement in relation to the ground.
hover check Used to describe when a helicopter/ VTOL aircraft requires a stabilized hover to conduct a performance/power check prior to hover taxi, air taxi, or takeoff. Altitude of the hover will vary based on the purpose of the check.
hover taxi Used to describe a helicopter/VTOL aircraft movement conducted above the surface and in ground effect at airspeeds less than approximately 20 knots. The actual height may vary and some helicopters may require hover taxi above 25 feet AGL to reduce ground effect turbulence or provide clearance for cargo slingloads.
hovering ceiling The maximum altitude at which a helicopter can support itself without forward motion.
hovering outside of ground effect Hovering greater than one rotor diameter distance above the surface. Because induced drag is greater while hovering out of ground effect, it takes more power to achieve a hover out of ground effect.
how do you hear me? A question relating to the quality of the transmission or to determine how well the transmission is being received.
hub In helicopters, the part of a propeller or rotor system that attaches to the main driving shaft and to which the blades are fastened.
Huck Lockbolt A patented, threadless bolt used in the production of aircraft where quickly installed high-strength, lightweight fasteners are required.
HUD Heads up display. A system that displays flight information on a transparent display in the line-of-sight of the pilot so that information can be read without looking down into the cockpit. Newest terminology is Head-up Guidance System (HGS).
hue 1. The gradation of colors. 2. The characteristics of a color that differentiates between red, blue, or yellow and any of the intermediate colors.
human factors The study of how people interact with their environments. In the case of general aviation, it is the study of how pilot performance is influenced by such issues as the design of cockpits, the function of the organs of the body, the effects of emotions, and the interaction and communication with other participants in the aviation community, such as other crew members and air traffic control personnel.
human factors related The phrase human factors related more aptly describes an accident since it is not usually a single decision that leads to an accident, but a chain of events triggered by a number of factors. The poor judgment chain, sometimes referred to as the error chain, is a term used to describe this principle of contributing factors in a human factors related accident.
humidifier A device used to increase the humidity of the air. Humidifiers are primarily used in air-cycle air conditioning systems to increase the comfort within the cabin.
humidity The amount of water vapor in the air.
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.
hunting 1. An undesirable oscillation above and below a desired value in a control system. 2. An oscillatory motion of an articulated rotor s blades about the Alpha Hinge caused by coriolis forces.
hurricane A tropical cyclone in the Western Hemisphere with winds in excess of 65 knots.
hurricane eye The circular, nearly cloud free region approximately 10 to 20 nautical miles in diameter, located in the center of the storm.
hurricane warning The warning issued within 24 hours of the arrival of hurricane conditions.
hurricane watch Issued when hurricane conditions are expected in a particular area within a day or more.
hybrid In composites, the combination of two or more types of reinforcing materials into the composite structure.
hydraulic booster unit A unit for moving the flight controls in a large, high-speed aircraft. It is actuated by the normal cockpit controls but greatly amplifies the force the pilot exerts.
hydraulic brake An aircraft brake operated by means of hydraulic fluid under pressure.
hydraulic filter A unit that removes foreign particles from the hydraulic system.
hydraulic fluid A liquid used to transmit and distribute forces to various units being actuated.
hydraulic fuse A unit designed to stop the flow of hydraulic fluid if a leak occurs downstream of the fuse.
hydraulic lock A condition that occurs in a reciprocating engine having cylinders below the crankcase. Oil leaks past the piston rings and fills the cylinder with an incompressible fluid. The engine cannot then be rotated without damage.
hydraulic motor A motor driven by a flow of hydraulic fluid.
hydraulic pump An engine-driven, electric motor-driven, or hand-operated pump used to move hydraulic fluid through a system.
hydraulic reservoir A container for the hydraulic fluid supply in an aircraft.
hydraulic system An aircraft s entire fluid power system, including the reservoir, pump, control valves, actuators, and all of the associated plumbing.
hydraulic valve lifter The hydraulic units in the valve train of a reciprocating aircraft engine used to automatically adjust for any changes in dimensions of the engine caused by expansion and also to keep the operating clearance in the valve mechanism at zero.
hydraulics The branch of science that deals with the transmission of power by incompressible fluids under pressure.
hydrocarbon An organic compound that consists mostly of carbon and hydrogen. The vast majority of our fossil fuels, including gasoline and turbine fuel, are hydrocarbons.
hydrodynamics The study of forces produced by incompressible fluids in motion.
hydrofoil An airfoil-shaped plate attached to the bottom of an airplane or boat that lifts the vehicle out of the water by hydrodynamic action when the vehicle is moved through the water at high speed.
hydrogen A basic element with a symbol of H and an atomic number of 1. In chemical formulas, free hydrogen appears as H2 because there must be two atoms of hydrogen to form one molecule of free hydrogen gas.
hydrogen bomb A nuclear weapon that produces heat and light from the fusion of hydrogen atoms.
hydrogen brazing Braze welding in which hydrogen is used as the fuel gas.
hydrogen embrittlement A brittle condition caused by the metal absorbing hydrogen while it is being electroplated.
hydrogen fuel A proposed jet fuel of the future that could be stored as a gas or cryogenic liquid. The present high cost and storage problems prevent its current use.
hydrogen peroxide H2O2. An unstable compound used as an oxidizing agent, antiseptic, and a fuel for rocket engines.
hydrological cycle The movement of moisture from the earth to the atmosphere and back to the earth again.
hydromechanical fuel control A fuel control that utilizes hydraulic and mechanical forces to operate its fuel scheduling mechanisms.
hydrometeor Atmospheric water vapor. Liquid or solid water formation that is suspended in, or falling from, the air, including clouds, fog, ice fog, mist, rain, and hail also any water particles blown by the wind from the Earth s surface.
hydrometer A device used to measure specific gravity of a liquid. It consists of a weighted float with a long stem in the enlarged glass tube of a syringe. Liquid is pulled up into the tube and the float rides vertically on the surface. The amount the float is submerged is a function of the density of the liquid. The number on the float s stem opposite the liquid level is the specific gravity.
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.
hydropneumatic Mechanical equipment that uses both hydraulic and pneumatic forces in order to accomplish its intended purpose.
hydro-ski A hydrofoil mounted below the hull of a flying boat, which hydrodynamically produces lift by the hydro-ski. As the flying boat begins to move through the water, the hydro-ski helps to lift the hull out of the water.
hydro-sorb A hydraulic shock absorber used in a bungee shock cord landing gear to prevent rebound.
hydrostatic testing The method of pressure-testing compressed gas cylinders with high-pressure water rather than a compressible fluid such as air. Water is used for safety reasons.
hydroxide A chemical compound made up of a metal or a non-metal (acid) base and a negative hydroxyl ion (OH).
hygrometer An instrument used to determine the amount of moisture in the air.
hygroscopic material A material such as silica gel that absorbs moisture from the air.
hypergolic A self-igniting reaction upon contact of the components, without the presence of a spark.
hypersonic A regime of flight where speeds of Mach 5.00 are exceeded.
hypersonic engine An engine designed to operate in the speed range above Mach 5. One possibility is the variable cycle engine. This engine functions as a turbojet up to perhaps Mach 3, then as doors close off the compressor inlet, it operates from a ramjet-type duct surrounding the engine.
hypersonic flight Flight at speeds of Mach 5 or above.
hypersonic flow Flow at very high supersonic speeds. Mach 5 or above.
hyperventilation Breathing at such an excess rate that the normal amount of carbon dioxide is depleted from the blood.
hypotenuse The side of a 90 (right) triangle opposite the right angle.
hypoxia A lack of sufficient oxygen reaching the body tissues.
hysteresis loop A graph of the magnetic characteristics of a material.