This is an HTML conversion of the official Airplane Flying Handbook (FAA-H-8083-3A) Glossary as published by the FAA. The FAA only publishes it as a PDF, but we've meticulously carefully converted to HTML for your convenience.

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This glossary is based on our retrieval the official FAA publication from on their web site on July 11th, 2023 from URL: https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/20_afh_glossary.pdf

The last modified date of the PDF when we retrieved it was 03/25/2022 12:36:53 and the FAA internal ID was 10DE022EFCC3F9932638B9DC60F26C25

We've attempt to reproduce the official FAA PDF as exactly as possible with only the following changes and corrections:

In the 14 CFR definition we have added a closing parenthesis, we believe was omitted in error.
In the Energy balance equation term there was a colon rather than a period as with all other terms and we've corrected this for consistency.
We have eliminated subscripts, to match the way most people write and type these terms, for example V₁has been replaced with V1.

If you find any errors, please leave a comment and we'll correct it!

FAA Aviation Glossary

Term	Definition
14 CFR.	(Title 14 of the Code of Federal Regulations.) Federal regulations pertaining to aviation activity. Previously known as Federal Aviation Regulations.
100-Hour Inspection.	An inspection, identical in scope to an annual inspection. Must be conducted every 100 hours of flight on aircraft of under 12,500 pounds that are used for hire.
Absolute altitude.	The vertical distance of an airplane above the terrain or above ground level (AGL).
Absolute ceiling.	The altitude at which a climb is no longer possible.
Accelerate-go distance.	The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1 and continue the takeoff on the remaining engine(s). The runway required includes the distance required to climb to 35 feet by which time V2 speed must be attained.
Accelerate-stop distance.	The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and abort the takeoff and bring the airplane to a stop using braking action only (use of thrust reversing is not considered).
Acceleration.	Force involved in overcoming inertia, and which may be defined as a change in velocity per unit of time.
Accessories.	Components that are used with an engine, but are not a part of the engine itself. Units such as magnetos, carburetors, generators, and fuel pumps are commonly installed engine accessories.
Adjustable stabilizer.	A stabilizer that can be adjusted in flight to trim the airplane, thereby allowing the airplane to fly hands-off at any given airspeed.
Adverse yaw.	A condition of flight in which the nose of an airplane tends to yaw toward the outside of the turn. This is caused by the higher induced drag on the outside wing, which is also producing more lift. Induced drag is a by-product of the lift associated with the outside wing.
Aerodynamic ceiling.	The point (altitude) at which, as the indicated airspeed decreases with altitude, it progressively merges with the low speed buffet boundary where pre-stall buffet occurs for the airplane at a load factor of 1.0 G.
Aerodynamics.	The science of the action of air on an object, and with the motion of air on other gases. Aerodynamics deals with the production of lift by the aircraft, the relative wind, and the atmosphere.
Ailerons.	Primary flight control surfaces mounted on the trailing edge of an airplane wing, near the tip. Ailerons control roll about the longitudinal axis.
Air start.	The act or instance of starting an aircraft’s engine while in flight, especially a jet engine after flameout.
Aircraft energy management.	The process of planning, monitoring and controlling altitude and airspeed in relation to the airplane’s energy state. Note that this definition is concerned with managing mechanical energy (altitude and airspeed) and addresses the safety (flight control) side of energy management. It does not address the efficiency (aircraft performance) side of energy management, which is concerned with how efficiently the engine generates mechanical energy from fuel and how efficiently the airframe spends that energy in flight.
Aircraft logbooks.	Journals containing a record of total operating time, repairs, alterations or inspections performed, and all Airworthiness Directive (AD) notes complied with. A maintenance logbook should be kept for the airframe, each engine, and each propeller.
Airfoil.	An airfoil is any surface, such as a wing, propeller, rudder, or even a trim tab, which provides aerodynamic force when it interacts with a moving stream of air.
Airmanship.	A sound acquaintance with the principles of flight, the ability to operate an airplane with competence and precision both on the ground and in the air, and the exercise of sound judgment that results in optimal operational safety and efficiency.
Airplane Flight Manual (AFM).	A document developed by the airplane manufacturer and approved by the Federal Aviation Administration (FAA). It is specific to a particular make and model airplane by serial number and it contains operating procedures and limitations.
Airplane Owner/Information Manual.	A document developed by the airplane manufacturer containing general information about the make and model of an airplane. The airplane owner’s manual is not FAA-approved and is not specific to a particular serial numbered airplane. This manual is not kept current, and therefore cannot be substituted for the AFM/POH.
Airworthiness Certificate.	A certificate issued by the FAA to all aircraft that have been proven to meet the minimum standards set down by the Code of Federal Regulations.
Airworthiness Directive.	A regulatory notice sent out by the FAA to the registered owner of an aircraft informing the owner of a condition that prevents the aircraft from continuing to meet its conditions for airworthiness. Airworthiness Directives (AD) must be complied with within the required time limit, and the fact of compliance, the date of compliance, and the method of compliance must be recorded in the aircraft’s maintenance records.
Airworthiness.	A condition in which the aircraft conforms to its type certificated design including supplemental type certificates and field-approved alterations. The aircraft must also be in a condition for safe flight as determined by annual, 100-hour, preflight and any other required inspections.
Alpha mode of operation.	The operation of a turboprop engine that includes all of the flight operations, from takeoff to landing. Alpha operation is typically between 95 percent to 100 percent of the engine operating speed.
Alternate air.	A device which opens, either automatically or manually, to allow induction airflow to continue should the primary induction air opening become blocked.
Alternate static source.	A manual port that when opened allows the pitot static instruments to sense static pressure from an alternate location should the primary static port become blocked.
Alternator/generator.	A device that uses engine power to generate electrical power.
Altimeter.	A flight instrument that indicates altitude by sensing pressure changes.
Altitude (AGL).	The actual height above ground level (AGL) at which the aircraft is flying.
Altitude (MSL).	The actual height above mean sea level (MSL) at which the aircraft is flying.
Altitude chamber.	A device that simulates high altitude conditions by reducing the interior pressure. The occupants will suffer from the same physiological conditions as flight at high altitude in an unpressurized aircraft.
Altitude engine.	A reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.
Angle of attack.	The acute angle between the chord line of the airfoil and the direction of the relative wind.
Angle of incidence.	The angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.
Annual inspection.	Except as provided in regulation, no person may operate an aircraft unless, within the preceding 12 calendar months, it has had an annual inspection, per 14 CFR part 91, section 91.409(a). This inspection is normally performed every 12 calendar months by an A&P technician holding an Inspection Authorization (14 CFR part 65, section 65.95(a)(2)).
Anti-icing.	The prevention of the formation of ice on a surface. Ice may be prevented by using heat or by covering the surface with a chemical that prevents water from reaching the surface. Anti-icing should not be confused with deicing, which is the removal of ice after it has formed on the surface.
Attitude indicator.	An instrument which uses an artificial horizon and miniature airplane to depict the position of the airplane in relation to the true horizon. The attitude indicator senses roll as well as pitch, which is the up and down movement of the airplane’s nose.
Attitude.	The position of an aircraft as determined by the relationship of its axes and a reference, usually the earth’s horizon.
Autokinesis.	This is caused by staring at a single point of light against a dark background for more than a few seconds. After a few moments, the light appears to move on its own.
Autopilot.	An automatic flight control system which keeps an aircraft in level flight or on a set course. Automatic pilots can be directed by the pilot, or they may be coupled to a radio navigation signal.
Axes of an aircraft.	Three imaginary lines that pass through an aircraft’s center of gravity. The axes can be considered as imaginary axles around which the aircraft turns. The three axes pass through the center of gravity at 90° angles to each other. The axis from nose to tail is the longitudinal axis, the axis that passes from wingtip to wingtip is the lateral axis, and the axis that passes vertically through the center of gravity is the vertical axis.
Axial flow compressor.	A type of compressor used in a turbine engine in which the airflow through the compressor is essentially linear. An axial-flow compressor is made up of several stages of alternate rotors and stators. The compressor ratio is determined by the decrease in area of the succeeding stages.
Back side of the power curve.	Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.
Balked landing.	A go-around.
Ballast.	Removable or permanently installed weight in an aircraft used to bring the center of gravity into the allowable range.
Balloon.	The result of a too aggressive flare during landing causing the aircraft to climb.
Basic empty weight (GAMA).	Basic empty weight includes the standard empty weight plus optional and special equipment that has been installed.
Best angle of climb (VX).	The speed at which the aircraft will produce the most gain in altitude in a given distance.
Best glide.	The airspeed in which the aircraft glides the furthest for the least altitude lost when in non-powered flight. Best rate of climb (VY). The speed at which the aircraft will produce the most gain in altitude in the least amount of time. Blade face. The flat portion of a propeller blade, resembling the bottom portion of an airfoil.
Bleed air.	Compressed air tapped from the compressor stages of a turbine engine by use of ducts and tubing. Bleed air can be used for deice, anti-ice, cabin pressurization, heating, and cooling systems.
Bleed valve.	In a turbine engine, a flapper valve, a pop off valve, or a bleed band designed to bleed off a portion of the compressor air to the atmosphere. Used to maintain blade angle of attack and provide stall-free engine acceleration and deceleration.
Boost pump.	An electrically driven fuel pump, usually of the centrifugal type, located in one of the fuel tanks. It is used to provide fuel to the engine for starting and providing fuel pressure in the event of failure of the engine driven pump. It also pressurizes the fuel lines to prevent vapor lock.
Buffeting.	The beating of an aerodynamic structure or surface by unsteady flow, gusts, etc.; the irregular shaking or oscillation of a vehicle component owing to turbulent air or separated flow.
Bus bar.	An electrical power distribution point to which several circuits may be connected. It is often a solid metal strip having a number of terminals installed on it.
Bus tie.	A switch that connects two or more bus bars. It is usually used when one generator fails and power is lost to its bus. By closing the switch, the operating generator powers both buses.
Bypass air.	The part of a turbofan’s induction air that bypasses the engine core.
Bypass ratio.	The ratio of the mass airflow in pounds per second through the fan section of a turbofan engine to the mass airflow that passes through the gas generator portion of the engine. Or, the ratio between fan mass airflow (lb/sec.) and core engine mass airflow (lb/sec.).
Cabin pressurization.	A condition where pressurized air is forced into the cabin simulating pressure conditions at a much lower altitude and increasing the aircraft occupants comfort.
Calibrated airspeed (CAS).	Indicated airspeed corrected for installation error and instrument error. Although manufacturers attempt to keep airspeed errors to a minimum, it is not possible to eliminate all errors throughout the airspeed operating range. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots. This error is generally greatest at low airspeeds. In the cruising and higher airspeed ranges, indicated airspeed and calibrated airspeed are approximately the same. Refer to the airspeed calibration chart to correct for possible airspeed errors.
Cambered.	The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.
Carburetor ice.	Ice that forms inside the carburetor due to the temperature drop caused by the vaporization of the fuel. Induction system icing is an operational hazard because it can cut off the flow of the fuel/air charge or vary the fuel/air ratio.
Carburetor.	1. Pressure: A hydromechanical device employing a closed feed system from the fuel pump to the discharge nozzle. It meters fuel through fixed jets according to the mass airflow through the throttle body and discharges it under a positive pressure. Pressure carburetors are distinctly different from float-type carburetors, as they do not incorporate a vented float chamber or suction pickup from a discharge nozzle located in the venturi tube. 2. Float-type: Consists essentially of a main air passage through which the engine draws its supply of air, a mechanism to control the quantity of fuel discharged in relation to the flow of air, and a means of regulating the quantity of fuel/air mixture delivered to the engine cylinders.
Cascade reverser.	A thrust reverser normally found on turbofan engines in which a blocker door and a series of cascade vanes are used to redirect exhaust gases in a forward direction.
Center of gravity (CG).	The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percent of mean aerodynamic chord (MAC). The location depends on the distribution of weight in the airplane.
Center-of-gravity limits.	The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.
Center-of-gravity range.	The distance between the forward and aft CG limits indicated on pertinent airplane specifications.
Centrifugal flow compressor.	An impeller-shaped device that receives air at its center and slings air outward at high velocity into a diffuser for increased pressure. Also referred to as a radial outflow compressor.
Chart Supplements.	A listing of data on record with the FAA on all open-to-the-public airports, seaplane bases, heliports, military facilities and selected private use airports specifically requested by the Department of Defense (DOD) for which a DOD instrument approach procedure has been published in the US. Terminal Procedures Publication, airport sketches, NAVAIDs, communications data, weather data sources, airspace, special notices, VFR waypoints, Airport Diagrams and operational procedures.
Chord line.	An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.
Circuit breaker.	A circuit-protecting device that opens the circuit in case of excess current flow. A circuit breaker differs from a fuse in that it can be reset without having to be replaced.
Clear air turbulence.	Turbulence not associated with any visible moisture.
Climb gradient.	The ratio between distance traveled and altitude gained.
Cockpit resource management.	Techniques designed to reduce pilot errors and manage errors that do occur utilizing cockpit human resources. The assumption is that errors are going to happen in a complex system with error-prone humans.
Coefficient of lift.	See lift coefficient.
Coffin corner.	The flight regime where any increase in airspeed will induce high speed Mach buffet and any decrease in airspeed will induce low speed Mach buffet.
Combustion chamber.	The section of the engine into which fuel is injected and burned.
Common traffic advisory frequency (CTAF).	The common frequency used by airport traffic to announce position reports in the vicinity of the airport.
Complex aircraft.	An aircraft with retractable landing gear, flaps, and a controllable-pitch propeller, or one that is turbine-powered.
Compression ratio.	1. In a reciprocating engine, the ratio of the volume of an engine cylinder with the piston at the bottom center to the volume with the piston at top center. 2. In a turbine engine, the ratio of the pressure of the air at the discharge to the pressure of air at the inlet.
Compressor bleed air.	See bleed air.
Compressor bleed valves.	See bleed valve.
Compressor section.	The section of a turbine engine that increases the pressure and density of the air flowing through the engine.
Compressor stall.	In gas turbine engines, a condition in an axial-flow compressor in which one or more stages of rotor blades fail to pass air smoothly to the succeeding stages. A stall condition is caused by a pressure ratio that is incompatible with the engine rpm Compressor stall will be indicated by a rise in exhaust temperature or rpm fluctuation, and if allowed to continue, may result in flameout and physical damage to the engine.
Compressor surge.	A severe compressor stall across the entire compressor that can result in severe damage if not quickly corrected. This condition occurs with a complete stoppage of airflow or a reversal of airflow.
Condition lever.	In a turbine engine, a powerplant control that controls the flow of fuel to the engine. The condition lever sets the desired engine rpm within a narrow range between that appropriate for ground and flight operations.
Configuration.	This is a general term, which normally refers to the position of the landing gear and flaps.
Constant speed propeller.	A controllable-pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant rpm in spite of varying air loads.
Control touch.	The ability to sense the action of the airplane and its probable actions in the immediate future, with regard to attitude and speed variations, by sensing and evaluation of varying pressures and resistance of the control surfaces transmitted through the cockpit flight controls.
Controllability.	A measure of the response of an aircraft relative to the pilot’s flight control inputs.
Controllable-pitch propeller.	A propeller in which the blade angle can be changed during flight by a control in the cockpit.
Conventional landing gear.	Landing gear employing a third rear-mounted wheel. These airplanes are also sometimes referred to as tailwheel airplanes.
Coordinated flight.	Application of all appropriate flight and power controls to prevent slipping or skidding in any flight condition.
Coordination.	The ability to use the hands and feet together subconsciously and in the proper relationship to produce desired results in the airplane.
Core airflow.	Air drawn into the engine for the gas generator.
Cowl flaps.	Devices arranged around certain air-cooled engine cowlings which may be opened or closed to regulate the flow of air around the engine.
Crab.	A flight condition in which the nose of the airplane is pointed into the wind a sufficient amount to counteract a crosswind and maintain a desired track over the ground.
Crazing.	Small fractures in aircraft windshields and windows caused from being exposed to the ultraviolet rays of the sun and temperature extremes.
Critical altitude.	The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.
Critical angle of attack.	The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.
Critical engine.	The engine whose failure has the most adverse effect on directional control.
Cross controlled.	A condition where aileron deflection is in the opposite direction of rudder deflection. Crossfeed. A system that allows either engine on a twin- engine airplane to draw fuel from any fuel tank. Crosswind component. The wind component, measured in knots, at 90° to the longitudinal axis of the runway.
Current limiter.	A device that limits the generator output to a level within that rated by the generator manufacturer.
Datum (reference datum).	An imaginary vertical plane or line from which all measurements of moment arm are taken. The datum is established by the manufacturer. Once the datum has been selected, all moment arms and the location of CG range are measured from this point.
Decompression sickness.	A condition where the low pressure at high altitudes allows bubbles of nitrogen to form in the blood and joints causing severe pain. Also known as the bends.
Deicer boots.	Inflatable rubber boots attached to the leading edge of an airfoil. They can be sequentially inflated and deflated to break away ice that has formed over their surface.
Deicing.	Removing ice after it has formed.
Delamination.	The separation of layers.
Density altitude.	This altitude is pressure altitude corrected for variations from standard temperature. When conditions are standard, pressure altitude and density altitude are the same. If the temperature is above standard, the density altitude is higher than pressure altitude. If the temperature is below standard, the density altitude is lower than pressure altitude. This is an important altitude because it is directly related to the airplane’s performance.
Designated pilot examiner (DPE).	An individual designated by the FAA to administer practical tests to pilot applicants.
Detonation.	The sudden release of heat energy from fuel in an aircraft engine caused by the fuel-air mixture reaching its critical pressure and temperature. Detonation occurs as a violent explosion rather than a smooth burning process.
Dewpoint.	The temperature at which air can hold no more water.
Differential ailerons.	Control surface rigged such that the aileron moving up moves a greater distance than the aileron moving down. The up aileron produces extra parasite drag to compensate for the additional induced drag caused by the down aileron. This balancing of the drag forces helps minimize adverse yaw.
Diffusion.	Reducing the velocity of air causing the pressure to increase.
Directional stability.	Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state. The vertical tail is the primary contributor to directional stability, causing an airplane in flight to align with the relative wind.
Ditching.	Emergency landing in water.
Downwash.	Air deflected perpendicular to the motion of the airfoil.
Drag curve.	A visual representation of the amount of drag of an aircraft at various airspeeds.
Drag.	An aerodynamic force on a body acting parallel and opposite to the relative wind. The resistance of the atmosphere to the relative motion of an aircraft. Drag opposes thrust and limits the speed of the airplane.
Drift angle.	Angle between heading and track.
Ducted-fan engine.	An engine-propeller combination that has the propeller enclosed in a radial shroud. Enclosing the propeller improves the efficiency of the propeller.
Dutch roll.	A combination of rolling and yawing oscillations that normally occurs when the dihedral effects of an aircraft are more powerful than the directional stability. Usually dynamically stable but objectionable in an airplane because of the oscillatory nature.
Dynamic 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.
Dynamic stability.	The property of an aircraft that causes it, when disturbed from straight-and-level flight, to develop forces or moments that restore the original condition of straight and level.
Electrical bus.	See bus bar.
Electrohydraulic.	Hydraulic control which is electrically actuated.
Elevator.	The horizontal, movable primary control surface in the tail section, or empennage, of an airplane. The elevator is hinged to the trailing edge of the fixed horizontal stabilizer.
Emergency locator transmitter.	A small, self-contained radio transmitter that will automatically, upon the impact of a crash, transmit an emergency signal on 121.5, 243.0, or 406.0 MHz.
Empennage.	The section of the airplane that consists of the vertical stabilizer, the horizontal stabilizer, and the associated control surfaces.
Energy balance equation.	According to this equation, the net transfer of mechanical energy into and out of the airplane (a function of thrust minus drag) is always equal to the change in its total mechanical energy (a function of altitude and airspeed).
Energy distribution error.	An energy error where the total mechanical energy is correct, but the distribution between potential (altitude) and kinetic energy (airspeed) is not correct relative to the intended altitude-speed profile. When this error occurs, the pilot will observe that altitude and airspeed deviate in opposite directions (e.g., higher and slower than desired; or lower and faster than desired). An example would be an airplane on final approach that is above the desired glide slope and at a slower airspeed than desired.
Energy error.	An altitude and/or airspeed deviation from an intended target expressed in terms of energy. Depending on the airplane’s total amount of energy and its distribution between altitude and airspeed, energy errors are classified as total energy errors, energy distribution errors, or a combination of both errors.
Energy exchange.	Trading one form of energy (e.g., altitude) for another form (e.g., airspeed).
Energy height or total specific energy (ES).	Measured in units of height (e.g., feet), it represents the airplane’s total energy per unit weight. It is found by dividing the sum of potential energy and kinetic energy by the airplane’s weight. It also represents the maximum height that an airplane would reach from its current altitude, if it were to trade all its speed for altitude.
Energy state.	The airplane’s total mechanical energy and its distribution between altitude and airspeed.
Energy system.	A flying airplane is an open energy system. That means that the airplane can gain energy from some source (e.g., fuel) and lose energy to the environment (e.g., surrounding air) . In addition, energy can be added to or removed from the airplane’s total mechanical energy stored as altitude and airspeed.
Engine pressure ratio (EPR).	The ratio of turbine discharge pressure divided by compressor inlet pressure that is used as an indication of the amount of thrust being developed by a turbine engine.
Environmental systems.	In an aircraft, the systems, including the supplemental oxygen systems, air conditioning systems, heaters, and pressurization systems, which make it possible for an occupant to function at high altitude.
Equilibrium.	A condition that exists within a body when the sum of the moments of all of the forces acting on the body is equal to zero. In aerodynamics, equilibrium is when all opposing forces acting on an aircraft are balanced (steady, unaccelerated flight conditions).
Equivalent shaft horsepower (ESHP).	A measurement of the total horsepower of a turboprop engine, including that provided by jet thrust.
Exhaust gas temperature (EGT).	The temperature of the exhaust gases as they leave the cylinders of a reciprocating engine or the turbine section of a turbine engine.
Exhaust manifold.	The part of the engine that collects exhaust gases leaving the cylinders.
Exhaust.	The rear opening of a turbine engine exhaust duct. The nozzle acts as an orifice, the size of which determines the density and velocity of the gases as they emerge from the engine.
False horizon.	An optical illusion where the pilot confuses a row of lights along a road or other straight line as the horizon.
False start.	See hung start.
Feathering propeller (feathered).	A controllable pitch propeller with a pitch range sufficient to allow the blades to be turned parallel to the line of flight to reduce drag and prevent further damage to an engine that has been shut down after a malfunction.
Fixation.	A psychological condition where the pilot fixes attention on a single source of information and ignores all other sources.
Fixed-shaft turboprop engine.	A turboprop engine where the gas producer spool is directly connected to the output shaft.
Fixed-pitch propellers.	Propellers with fixed blade angles. Fixed-pitch propellers are designed as climb propellers, cruise propellers, or standard propellers.
Flaps.	Hinged portion of the trailing edge between the ailerons and fuselage. In some aircraft, ailerons and flaps are interconnected to produce full-span “flaperons.” In either case, flaps change the lift and drag on the wing.
Flat pitch.	A propeller configuration when the blade chord is aligned with the direction of rotation.
Flicker vertigo.	A disorienting condition caused from flickering light off the blades of the propeller.
Flight director.	An automatic flight control system in which the commands needed to fly the airplane are electronically computed and displayed on a flight instrument. The commands are followed by the human pilot with manual control inputs or, in the case of an autopilot system, sent to servos that move the flight controls.
Flight idle.	Engine speed, usually in the 70-80 percent range, for minimum flight thrust.
Floating.	A condition when landing where the airplane does not settle to the runway due to excessive airspeed.
Force (F).	The energy applied to an object that attempts to cause the object to change its direction, speed, or motion. In aerodynamics, it is expressed as F, T (thrust), L (lift), W (weight), or D (drag), usually in pounds.
Form drag.	The part of parasite drag on a body resulting from the integrated effect of the static pressure acting normal to its surface resolved in the drag direction.
Forward slip.	A slip in which the airplane’s direction of motion continues the same as before the slip was begun. In a forward slip, the airplane’s longitudinal axis is at an angle to its flightpath.
Free power turbine engine.	A turboprop engine where the gas producer spool is on a separate shaft from the output shaft. The free power turbine spins independently of the gas producer and drives the output shaft.
Friction drag.	The part of parasitic drag on a body resulting from viscous shearing stresses over its wetted surface.
Frise-type aileron.	Aileron having the nose portion projecting ahead of the hinge line. When the trailing edge of the aileron moves up, the nose projects below the wing’s lower surface and produces some parasite drag, decreasing the amount of adverse yaw.
Fuel control unit.	The fuel-metering device used on a turbine engine that meters the proper quantity of fuel to be fed into the burners of the engine. It integrates the parameters of inlet air temperature, compressor speed, compressor discharge pressure, and exhaust gas temperature with the position of the cockpit power control lever.
Fuel efficiency.	Defined as the amount of fuel used to produce a specific thrust or horsepower divided by the total potential power contained in the same amount of fuel.
Fuel heater.	A radiator-like device which has fuel passing through the core. A heat exchange occurs to keep the fuel temperature above the freezing point of water so that entrained water does not form ice crystals, which could block fuel flow.
Fuel injection.	A fuel metering system used on some aircraft reciprocating engines in which a constant flow of fuel is fed to injection nozzles in the heads of all cylinders just outside of the intake valve. It differs from sequential fuel injection in which a timed charge of high-pressure fuel is sprayed directly into the combustion chamber of the cylinder.
Fuel load.	The expendable part of the load of the airplane. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.
Fuel tank sump.	A sampling port in the lowest part of the fuel tank that the pilot can utilize to check for contaminants in the fuel.
Fuselage.	The section of the airplane that consists of the cabin and/or cockpit, containing seats for the occupants and the controls for the airplane.
Gas generator.	The basic power producing portion of a gas turbine engine and excluding such sections as the inlet duct, the fan section, free power turbines, and tailpipe. Each manufacturer designates what is included as the gas generator, but generally consists of the compressor, diffuser, combustor, and turbine.
Gas turbine engine.	A form of heat engine in which burning fuel adds energy to compressed air and accelerates the air through the remainder of the engine. Some of the energy is extracted to turn the air compressor, and the remainder accelerates the air to produce thrust. Some of this energy can be converted into torque to drive a propeller or a system of rotors for a helicopter.
Glide ratio.	The ratio between distance traveled and altitude lost during non-powered flight.
Glidepath.	The path of an aircraft relative to the ground while approaching a landing.
Global position system (GPS).	A satellite-based radio positioning, navigation, and time-transfer system.
Go-around.	Terminating a landing approach.
Governing range.	The range of pitch a propeller governor can control during flight.
Governor.	A control which limits the maximum rotational speed of a device.
Gross weight.	The total weight of a fully loaded aircraft including the fuel, oil, crew, passengers, and cargo.
Ground adjustable trim tab.	A metal trim tab on a control surface that is not adjustable in flight. Bent in one direction or another while on the ground to apply trim forces to the control surface.
Ground effect.	A condition of improved performance encountered when an airplane is operating very close to the ground. When an airplane’s wing is under the influence of ground effect, there is a reduction in upwash, downwash, and wingtip vortices. As a result of the reduced wingtip vortices, induced drag is reduced.
Ground idle.	Gas turbine engine speed usually 60-70 percent of the maximum rpm range, used as a minimum thrust setting for ground operations.
Ground loop.	A sharp, uncontrolled change of direction of an airplane on the ground.
Ground power unit (GPU).	A type of small gas turbine whose purpose is to provide electrical power, and/or air pressure for starting aircraft engines. A ground unit is connected to the aircraft when needed. Similar to an aircraft-installed auxiliary power unit.
Ground track.	The aircraft’s path over the ground when in flight.
Groundspeed (GS).	The actual speed of the airplane over the ground. It is true airspeed adjusted for wind. Groundspeed decreases with a headwind, and increases with a tailwind.
Gust penetration speed.	The speed that gives the greatest margin between the high and low Mach speed buffets.
Gyroscopic precession.	An inherent quality of rotating bodies, which causes an applied force to be manifested 90º in the direction of rotation from the point where the force is applied.
Hand propping.	Starting an engine by rotating the propeller by hand.
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.
Heading.	The direction in which the nose of the aircraft is pointing during flight.
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 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.
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.
Igniter plugs.	The electrical device used to provide the spark for starting combustion in a turbine engine. Some igniters resemble spark plugs, while others, called glow plugs, have a coil of resistance wire that glows red hot when electrical current flows through the coil.
Impact ice.	Ice that forms on the wings and control surfaces or on the carburetor heat valve, the walls of the air scoop, or the carburetor units during flight. Impact ice collecting on the metering elements of the carburetor may upset fuel metering or stop carburetor fuel flow.
Inclinometer.	An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.
Indicated airspeed (IAS).	The direct instrument reading obtained from the airspeed indicator, uncorrected for variations in atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining airplane performance. Takeoff, landing, and stall speeds listed in the AFM or POH are indicated airspeeds and do not normally vary with altitude or temperature.
Indicated altitude.	The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting. Induced drag. That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed. Induction manifold. The part of the engine that distributes intake air to the cylinders.
Inertia.	The opposition which a body offers to a change of motion.
Initial climb.	This stage of the climb begins when the airplane leaves the ground and a pitch attitude has been established to climb away from the takeoff area.
Instrument Flight Rules (IFR).	Rules that govern the procedure for conducting flight in weather conditions below VFR weather.
minimums.	The term “IFR” also is used to define weather conditions and the type of flight plan under which an aircraft is operating.
Integral fuel tank.	A portion of the aircraft structure, usually a wing, which is sealed off and used as a fuel tank. When a wing is used as an integral fuel tank, it is called a “wet wing".
Intercooler.	A device used to reduce the temperature of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.
Internal combustion engine.	An engine that produces power as a result of expanding hot gases from the combustion of fuel and air within the engine itself. A steam engine where coal is burned to heat up water inside the engine is an example of an external combustion engine.
International Standard Atmosphere (ISA).	Standard atmospheric conditions consisting of a temperature of 59 °F (15 °C), and a barometric pressure of 29.92 "Hg. (1013.2 mb) at sea level. ISA values can be calculated for various altitudes using a standard lapse rate of approximately 2 °C per 1,000 feet.
Interstage turbine temperature (ITT).	The temperature of the gases between the high pressure and low pressure turbines.
Inverter.	An electrical device that changes DC to AC power.
Irreversible Deceleration and/or Sink Rate.	Unrecoverable depletion of mechanical energy as a result of continuous loss of airspeed and/or altitude coupled with insufficient excess power available under a given flight condition. Failure to recover above a certain critical AGL altitude results in the airplane hitting the ground regardless of what the pilot does.
Jet-powered airplane.	An aircraft powered by a turbojet or turbofan engine.
Kinesthesia.	The sensing of movements by feel.
Kinetic energy.	Amount of energy due to the airspeed, expressed as ½mV² where m = airplane’s mass and V = airspeed.
Lateral axis.	An imaginary line passing through the center of gravity of an airplane and extending across the airplane from wingtip to wingtip.
Lateral stability (rolling).	The stability about the longitudinal axis of an aircraft. Rolling stability or the ability of an airplane to return to level flight due to a disturbance that causes one of the wings to drop.
Lead-acid battery.	A commonly used secondary cell having lead as its negative plate and lead peroxide as its positive plate. Sulfuric acid and water serve as the electrolyte.
Leading edge devices.	High lift devices which are found on the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps.
Leading edge flap.	A portion of the leading edge of an airplane wing that folds downward to increase the camber, lift, and drag of the wing. The leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any given airspeed.
Leading edge.	The part of an airfoil that meets the airflow first.
Licensed empty weight.	The empty weight that consists of the airframe, engine(s), unusable fuel, and undrainable oil plus standard.
and optional equipment as specified in the equipment list.	Some manufacturers used this term prior to GAMA standardization.
Lift coefficient.	A coefficient representing the lift of a given airfoil. Lift coefficient is obtained by dividing the lift by the free-stream dynamic pressure and the representative area under consideration.
Lift.	One of the four main forces acting on an aircraft. On a fixed-wing aircraft, an upward force created by the effect of airflow as it passes over and under the wing.
Lift/drag ratio (L/D).	The efficiency of an airfoil section. It is the ratio of the coefficient of lift to the coefficient of drag for any given angle of attack.
Lift-off.	The act of becoming airborne as a result of the wings lifting the airplane off the ground, or the pilot rotating the nose up, increasing the angle of attack to start a climb.
Limit load factor.	Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs.
Load factor.	The ratio of the load supported by the airplane’s wings to the actual weight of the aircraft and its contents. Also referred to as G-loading.
Longitudinal axis.	An imaginary line through an aircraft from nose to tail, passing through its center of gravity. The longitudinal axis is also called the roll axis of the aircraft. Movement of the ailerons rotates an airplane about its longitudinal axis.
Longitudinal stability (pitching).	Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement.
Mach buffet.	Airflow separation behind a shock-wave pressure barrier caused by airflow over flight surfaces exceeding the speed of sound.
Mach compensating device.	A device to alert the pilot of inadvertent excursions beyond its certified maximum operating speed.
Mach critical.	The Mach speed at which some portion of the airflow over the wing first equals Mach 1.0. This is also the speed at which a shock wave first appears on the airplane.
Mach tuck.	A condition that can occur when operating a swept-wing airplane in the transonic speed range. A shock wave could form in the root portion of the wing and cause the air behind it to separate. This shock-induced separation causes the center of pressure to move aft. This, combined with the increasing amount of nose down force at higher speeds to maintain left flight, causes the nose to “tuck.” If not corrected, the airplane could enter a steep, sometimes unrecoverable dive.
Mach.	Speed relative to the speed of sound. Mach 1 is the speed of sound.
Magnetic compass.	A device for determining direction measured from magnetic north.
Main gear.	The wheels of an aircraft’s landing gear that supports the major part of the aircraft’s weight.
Maneuverability.	Ability of an aircraft to change directions along a flightpath and withstand the stresses imposed upon it.
Maneuvering speed (VA).	The maximum speed where full, abrupt control movement can be used without over-stressing the airframe. Manifold pressure (MP). The absolute pressure of the fuel/ air mixture within the intake manifold, usually indicated in inches of mercury.
Maximum allowable takeoff power.	The maximum power an engine is allowed to develop for a limited period of time; usually about one minute.
Maximum landing weight.	The greatest weight that an airplane normally is allowed to have at landing.
Maximum ramp weight.	The total weight of a loaded aircraft, including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and run-up operations. Ramp weight may also be referred to as taxi weight.
Maximum takeoff weight.	The maximum allowable weight for takeoff.
Maximum weight.	The maximum authorized weight of the aircraft and all of its equipment as specified in the Type Certificate Data Sheets (TCDS) for the aircraft.
Maximum zero fuel weight (GAMA).	The maximum weight, exclusive of usable fuel.
Minimum controllable airspeed.	An airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in an immediate stall.
Minimum drag speed (L/DMAX).	The point on the total drag curve where the lift-to-drag ratio is the greatest. At this speed, total drag is minimized.
Mixture.	The ratio of fuel to air entering the engine’s cylinders.
MMO.	Maximum operating speed expressed in terms of a decimal of Mach speed.
Moment arm.	The distance from a datum to the applied force.
Moment index (or index).	A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of airplanes where heavy items and long arms result in large, unmanageable numbers.
Moment.	The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.
Movable slat.	A movable auxiliary airfoil on the leading edge of a wing. It is closed in normal flight but extends at high angles of attack. This allows air to continue flowing over the top of the wing and delays airflow separation.
Mushing.	A flight condition caused by slow speed where the control surfaces are marginally effective.
N1, N2, N3.	Spool speed expressed in percent rpm. N1 on a turboprop is the gas producer speed. N1 on a turbofan or turbojet engine is the fan speed or low pressure spool speed. N2 is the high pressure spool speed on engine with 2 spools and medium pressure spool on engines with 3 spools with N3 being the high pressure spool.
Nacelle.	A streamlined enclosure on an aircraft in which an engine is mounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing.
Negative static stability.	The initial tendency of an aircraft to continue away from the original state of equilibrium after being disturbed.
Negative torque sensing (NTS).	A system in a turboprop engine that prevents the engine from being driven by the propeller. The NTS increases the blade angle when the propellers try to drive the engine.
Neutral static stability.	The initial tendency of an aircraft to remain in a new condition after its equilibrium has been disturbed.
Nickel-cadmium battery (NiCad).	A battery made up of alkaline secondary cells. The positive plates are nickel hydroxide, the negative plates are cadmium hydroxide, and potassium hydroxide is used as the electrolyte.
Normal category.	An airplane that has a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for nonacrobatic operation.
Normalizing (turbonormalizing).	A turbocharger that maintains sea level pressure in the induction manifold at altitude.
Octane.	The rating system of aviation gasoline with regard to its antidetonating qualities.
Overboost.	A condition in which a reciprocating engine has exceeded the maximum manifold pressure allowed by the manufacturer. Can cause damage to engine components.
Overspeed.	A condition in which an engine has produced more rpm than the manufacturer recommends, or a condition in which the actual engine speed is higher than the desired engine speed as set on the propeller control.
Overtemp.	A condition in which a device has reached a temperature above that approved by the manufacturer or any exhaust temperature that exceeds the maximum allowable for a given operating condition or time limit. Can cause internal damage to an engine.
Overtorque.	A condition in which an engine has produced more torque (power) than the manufacturer recommends, or a condition in a turboprop or turboshaft engine where the engine power has exceeded the maximum allowable for a given operating condition or time limit. Can cause internal damage to an engine.
Parasite drag.	That part of total drag created by the design or shape of airplane parts. Parasite drag increases with an increase in airspeed.
Payload (GAMA).	The weight of occupants, cargo, and baggage.
P-factor.	A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind. The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller.
Pilot’s Operating Handbook (POH).	A document developed by the airplane manufacturer and contains the FAA-approved Airplane Flight Manual (AFM) information.
Piston engine.	A reciprocating engine.
Pitch.	The rotation of an airplane about its lateral axis, or on a propeller, the blade angle as measured from plane of rotation.
Pivotal altitude.	A specific altitude at which, when an airplane turns at a given groundspeed, a projecting of the sighting reference line to a selected point on the ground will appear to pivot on that point.
Pneumatic system.	The power system in an aircraft used for operating such items as landing gear, brakes, and wing flaps with compressed air as the operating fluid.
Porpoising.	Oscillating around the lateral axis of the aircraft during landing.
Position lights.	Lights on an aircraft consisting of a red light on the left wing, a green light on the right wing, and a white light on the tail. CFRs require that these lights be displayed in flight from sunset to sunrise.
Positive static stability.	The initial tendency to return to a state of equilibrium when disturbed from that state.
Potential energy.	Amount of energy due to the altitude, expressed as mgh, where m = airplane’s mass, and g = gravitational constant, and h = altitude.
Power available.	The airplane’s rate of energy gain due to maximum available engine thrust at a given airspeed. Expressed as TV, where T = engine thrust, and V = airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.
Power distribution bus.	See bus bar.
Power lever.	The cockpit lever connected to the fuel control unit for scheduling fuel flow to the combustion chambers of a turbine engine.
Power required.	The airplane’s rate of energy loss due to total drag at a given airspeed. Expressed as DV, where D = total drag, and V = airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.
Power.	Implies work rate or units of work per unit of time, and as such, it is a function of the speed at which the force is developed. The term “power required” is generally associated with reciprocating engines.
Powerplant.	A complete engine and propeller combination with accessories.
Practical slip limit.	The maximum slip an aircraft is capable of performing due to rudder travel limits.
Precession.	The tilting or turning of a gyro in response to deflective forces causing slow drifting and erroneous indications in gyroscopic instruments.
Preignition.	Ignition occurring in the cylinder before the time of normal ignition. Preignition is often caused by a local hot spot in the combustion chamber igniting the fuel/air mixture.
Pressure altitude.	The altitude indicated when the altimeter setting window (barometric scale) is adjusted to 29.92. This is the altitude above the standard datum plane, which is a theoretical plane where air pressure (corrected to 15 ºC) equals 29.92 "Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.
Profile drag.	The total of the skin friction drag and form drag for a two-dimensional airfoil section.
Propeller blade angle.	The angle between the propeller chord and the propeller plane of rotation.
Propeller lever.	The control on a free power turbine turboprop that controls propeller speed and the selection for propeller feathering.
Propeller slipstream.	The volume of air accelerated behind a propeller producing thrust.
Propeller synchronization.	A condition in which all of the propellers have their pitch automatically adjusted to maintain a constant rpm among all of the engines of a multiengine aircraft.
Propeller.	A device for propelling an aircraft that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes the control components normally supplied by its manufacturer.
Ramp weight.	The total weight of the aircraft while on the ramp. It differs from takeoff weight by the weight of the fuel that will be consumed in taxiing to the point of takeoff.
Rate of turn.	The rate in degrees/second of a turn.
Reciprocating engine.	An engine that converts the heat energy from burning fuel into the reciprocating movement of the pistons. This movement is converted into a rotary motion by the connecting rods and crankshaft.
Reduction gear.	The gear arrangement in an aircraft engine that allows the engine to turn at a faster speed than the propeller.
Region of reverse command.	Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.
Registration certificate.	A State and Federal certificate that documents aircraft ownership.
Relative wind.	The direction of the airflow with respect to the wing. If a wing moves forward horizontally, the relative wind moves backward horizontally. Relative wind is parallel to and opposite the flightpath of the airplane.
Reverse thrust.	A condition where jet thrust is directed forward during landing to increase the rate of deceleration.
Reversing propeller.	A propeller system with a pitch change mechanism that includes full reversing capability. When the pilot moves the throttle controls to reverse, the blade angle changes to a pitch angle and produces a reverse thrust, which slows the airplane down during a landing.
Roll.	The motion of the aircraft about the longitudinal axis. It is controlled by the ailerons.
Roundout (flare).	A pitch-up during landing approach to reduce rate of descent and forward speed prior to touchdown.
Rudder.	The movable primary control surface mounted on the trailing edge of the vertical fin of an airplane. Movement of the rudder rotates the airplane about its vertical axis.
Ruddervator.	A pair of control surfaces on the tail of an aircraft arranged in the form of a V. These surfaces, when moved together by the control wheel, serve as elevators, and when moved differentially by the rudder pedals, serve as a rudder.
Runway centerline lights.	Runway centerline lights are installed on some precision approach runways to facilitate landing under adverse visibility conditions. They are located along the runway centerline and are spaced at 50-foot intervals. When viewed from the landing threshold, the runway centerline lights are white until the last 3,000 feet of the runway. The white lights begin to alternate with red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red.
Runway centerline markings.	The runway centerline identifies the center of the runway and provides alignment guidance during takeoff and landings. The centerline consists of a line of uniformly spaced stripes and gaps.
Runway edge lights.	Runway edge lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. These light systems are classified according to the intensity or brightness they are capable of producing: they are the High Intensity Runway Lights (HIRL), Medium Intensity Runway Lights (MIRL), and the Low Intensity Runway Lights (LIRL). The HIRL and MIRL systems have variable intensity controls, whereas the LIRLs normally have one intensity setting.
Runway end identifier lights (REIL).	One component of the runway lighting system. These lights are installed at many airfields to provide rapid and positive identification of the approach end of a particular runway.
Runway incursion.	Any occurrence at an airport involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in loss of separation with an aircraft taking off, intending to takeoff, landing, or intending to land.
Runway threshold markings.	Runway threshold markings come in two configurations. They either consist of eight longitudinal stripes of uniform dimensions disposed symmetrically about the runway centerline, or the number of stripes is related to the runway width. A threshold marking helps identify the beginning of the runway that is available for landing. In some instances, the landing threshold may be displaced.
Safety (SQUAT) switch.	An electrical switch mounted on one of the landing gear struts. It is used to sense when the weight of the aircraft is on the wheels.
Scan.	A procedure used by the pilot to visually identify all resources of information in flight.
Sea level.	A reference height used to determine standard atmospheric conditions and altitude measurements.
Segmented circle.	A visual ground based structure to provide traffic pattern information.
Service ceiling.	The maximum density altitude where the best rate-of-climb airspeed will produce a 100 feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.
Servo tab.	An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.
Shaft horse power (SHP).	Turboshaft engines are rated in shaft horsepower and calculated by use of a dynamometer device. Shaft horsepower is exhaust thrust converted to a rotating shaft.
Shock waves.	A compression wave formed when a body moves through the air at a speed greater than the speed of sound.
Sideslip.	A slip in which the airplane’s longitudinal axis remains parallel to the original flightpath, but the airplane no longer flies straight ahead. Instead, the horizontal component of wing lift forces the airplane to move sideways toward the low wing.
Single engine absolute ceiling.	The altitude that a twin engine airplane can no longer climb with one engine inoperative.
Single engine service ceiling.	The altitude that a twin engine airplane can no longer climb at a rate greater than 50 fpm with one engine inoperative.
Skid.	A condition where the tail of the airplane follows a path outside the path of the nose during a turn.
Slip.	An intentional maneuver to decrease airspeed or increase rate of descent, and to compensate for a crosswind on landing. A slip can also be unintentional when the pilot fails to maintain the aircraft in coordinated flight.
Specific excess power (PS).	Measured in feet per minute or feet per second, it represents rate of energy change—the ability of an airplane to climb or accelerate from a given flight condition. Available specific excess power is found by dividing the difference between power available and power required by the airplane’s weight.
Specific fuel consumption.	Number of pounds of fuel consumed in 1 hour to produce 1 HP.
Speed brakes.	A control system that extends from the airplane structure into the airstream to produce drag and slow the airplane.
Speed instability.	A condition in the region of reverse command where a disturbance that causes the airspeed to decrease causes total drag to increase, which in turn, causes the airspeed to decrease further.
Speed sense.	The ability to sense instantly and react to any reasonable variation of airspeed.
Speed.	The distance traveled in a given time.
Spin.	An aggravated stall that results in what is termed an “autorotation” wherein the airplane follows a downward corkscrew path. As the airplane rotates around the vertical axis, the rising wing is less stalled than the descending wing creating a rolling, yawing, and pitching motion.
Spiral instability.	A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.
Spiraling slipstream.	The slipstream of a propeller-driven airplane rotates around the airplane. This slipstream strikes the left side of the vertical fin, causing the airplane to yaw slightly. Vertical stabilizer offset is sometimes used by aircraft designers to counteract this tendency.
Split shaft turbine engine.	See free power turbine engine.
Spoilers.	High-drag devices that can be raised into the air flowing over an airfoil, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed. Spoilers are also used to shorten the ground roll after landing.
Spool.	A shaft in a turbine engine which drives one or more compressors with the power derived from one or more turbines.
Stabilator.	A single-piece horizontal tail surface on an airplane that pivots around a central hinge point. A stabilator serves the purposes of both the horizontal stabilizer and the elevator.
Stability.	The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flightpath. It is primarily an airplane design characteristic.
Stabilized approach.	A landing approach in which the pilot establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway. It is based on the pilot’s judgment of certain visual cues, and depends on the maintenance of a constant final descent airspeed and configuration.
Stall strips.	A spoiler attached to the inboard leading edge of some wings to cause the center section of the wing to stall before the tips. This assures lateral control throughout the stall.
Stall.	A rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed.
Standard atmosphere.	At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury ("Hg) or 1013.2 millibars, and a temperature of 15 °C (59 °F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1 "Hg and 2 °C (3.5 °F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) is 26.92 "Hg (29.92 – 3) and 9 °C (15 °C – 6 °C).
Standard day.	See standard atmosphere.
Standard empty weight (GAMA).	This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane; including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.
Standard weights.	These have been established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available.
Standard-rate turn.	A turn at the rate of 3º per second which enables the airplane to complete a 360º turn in 2 minutes.
Starter/generator.	A combined unit used on turbine engines. The device acts as a starter for rotating the engine, and after running, internal circuits are shifted to convert the device into a generator.
Static stability.	The initial tendency an aircraft displays when disturbed from a state of equilibrium.
Station.	A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.
Stick puller.	A device that applies aft pressure on the control column when the airplane is approaching the maximum operating speed.
Stick pusher.	A device that applies an abrupt and large forward force on the control column when the airplane is nearing an angle of attack where a stall could occur.
Stick shaker.	An artificial stall warning device that vibrates the control column.
Stress risers.	A scratch, groove, rivet hole, forging defect, or other structural discontinuity that causes a concentration of stress.
Subsonic.	Speed below the speed of sound.
Supercharger.	An engine- or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.
Supersonic.	Speed above the speed of sound.
Supplemental Type Certificate (STC).	A certificate authorizing an alteration to an airframe, engine, or component that has been granted an approved type certificate.
Swept-wing.	A wing planform in which the tips of the wing are farther back than the wing root.
Tailwheel aircraft.	See conventional landing gear.
Takeoff roll (ground roll).	The total distance required for an aircraft to become airborne.
Target reverser.	A thrust reverser in a jet engine in which clamshell doors swivel from the stowed position at the engine tailpipe to block all of the outflow and redirect some component of the thrust forward.
Taxiway lights.	Omnidirectional lights that outline the edges of the taxiway and are blue in color.
Taxiway turnoff lights.	Flush lights which emit a steady green color.
Tetrahedron.	A large, triangular-shaped, kite-like object installed near the runway. Tetrahedrons are mounted on a pivot and are free to swing with the wind to show the pilot the direction of the wind as an aid in takeoffs and landings.
Throttle.	The valve in a carburetor or fuel control unit that determines the amount of fuel-air mixture that is fed to the engine. Thrust line. An imaginary line passing through the center of the propeller hub, perpendicular to the plane of the propeller rotation. Thrust reversers. Devices which redirect the flow of jet exhaust to reverse the direction of thrust.
Thrust.	The force which imparts a change in the velocity of a mass. This force is measured in pounds but has no element of time or rate. The term, thrust required, is generally associated with jet engines. A forward force which propels the airplane through the air.
Timing.	The application of muscular coordination at the proper instant to make flight, and all maneuvers incident thereto, a constant smooth process.
Tire cord.	Woven metal wire laminated into the tire to provide extra strength. A tire showing any cord must be replaced prior to any further flight.
Torque meter.	An indicator used on some large reciprocating engines or on turboprop engines to indicate the amount of torque the engine is producing.
Torque sensor.	See torque meter.
Torque.	1. A resistance to turning or twisting. 2. Forces that produce a twisting or rotating motion. 3. In an airplane, the tendency of the aircraft to turn (roll) in the opposite direction of rotation of the engine and propeller.
Total drag.	The sum of the parasite and induced drag.
Total energy error.	An energy error where the total amount of mechanical energy is not correct. The airplane has too much or too little total energy relative to the intended altitude-speed profile. When this error occurs, the pilot will observe that altitude and airspeed deviate in the same direction (e.g., higher and faster than desired; or lower and slower than desired). An example would be an airplane on final approach that is above the desired glide slope and at a faster airspeed than desired.
Total mechanical energy.	Sum of the energy in altitude (potential energy) and the energy in airspeed (kinetic energy).
Touchdown zone lights.	Two rows of transverse light bars disposed symmetrically about the runway centerline in the runway touchdown zone.
Track.	The actual path made over the ground in flight.
Trailing edge.	The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.
Transition liner.	The portion of the combustor that directs the gases into the turbine plenum.
Transonic.	At the speed of sound.
Transponder.	The airborne portion of the secondary surveillance radar system. The transponder emits a reply when queried by a radar facility.
Tricycle gear.	Landing gear employing a third wheel located on the nose of the aircraft.
Trim tab.	A small auxiliary hinged portion of a movable control surface that can be adjusted during flight to a position resulting in a balance of control forces.
Triple spool engine.	Usually a turbofan engine design where the fan is the N1 compressor, followed by the N2 intermediate compressor, and the N3 high pressure compressor, all of which rotate on separate shafts at different speeds.
Tropopause.	The boundary layer between the troposphere and the mesosphere which acts as a lid to confine most of the water vapor, and the associated weather, to the troposphere.
Troposphere.	The layer of the atmosphere extending from the surface to a height of 20,000 to 60,000 feet depending on latitude.
True airspeed (TAS).	Calibrated airspeed corrected for altitude and nonstandard temperature. Because air density decreases with an increase in altitude, an airplane has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure. Therefore, for a given calibrated airspeed, true airspeed increases as altitude increases; or for a given true airspeed, calibrated airspeed decreases as altitude increases.
True altitude.	The vertical distance of the airplane above sea level—the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, and obstacle elevations on aeronautical charts are true altitudes.
T-tail.	An aircraft with the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T.
Turbine blades.	The portion of the turbine assembly that absorbs the energy of the expanding gases and converts it into rotational energy.
Turbine outlet temperature (TOT).	The temperature of the gases as they exit the turbine section.
Turbine plenum.	The portion of the combustor where the gases are collected to be evenly distributed to the turbine blades.
Turbine rotors.	The portion of the turbine assembly that mounts to the shaft and holds the turbine blades in place.
Turbine section.	The section of the engine that converts high pressure high temperature gas into rotational energy.
Turbocharger.	An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system.
Turbofan engine.	A turbojet engine in which additional propulsive thrust is gained by extending a portion of the compressor or turbine blades outside the inner engine case. The extended blades propel bypass air along the engine axis but between the inner and outer casing. The air is not combusted but does provide additional thrust.
Turbojet engine.	A jet engine incorporating a turbine-driven air compressor to take in and compress air for the combustion of fuel, the gases of combustion being used both to rotate the turbine and create a thrust producing jet.
Turboprop engine.	A turbine engine that drives a propeller through a reduction gearing arrangement. Most of the energy in the exhaust gases is converted into torque, rather than its acceleration being used to propel the aircraft.
Turbulence.	An occurrence in which a flow of fluid is unsteady.
Turn coordinator.	A rate gyro that senses both roll and yaw due to the gimbal being canted. Has largely replaced the turn-and-slip indicator in modern aircraft.
Turn-and-slip indicator.	A flight instrument consisting of a rate gyro to indicate the rate of yaw and a curved glass inclinometer to indicate the relationship between gravity and centrifugal force. The turn-and-slip indicator indicates the relationship between angle of bank and rate of yaw. Also called a turn-and-bank indicator.
Turning error.	One of the errors inherent in a magnetic compass caused by the dip compensating weight. It shows up only on turns to or from northerly headings in the Northern Hemisphere and southerly headings in the Southern Hemisphere. Turning error causes the compass to lead turns to the north or south and lag turns away from the north or south.
Ultimate load factor.	In stress analysis, the load that causes physical breakdown in an aircraft or aircraft component during a strength test, or the load that according to computations, should cause such a breakdown.
Unfeathering accumulator.	Tanks that hold oil under pressure which can be used to unfeather a propeller.
UNICOM.	A nongovernment air/ground radio communication station which may provide airport information at public use airports where there is no tower or FSS.
Unusable fuel.	Fuel that cannot be consumed by the engine. This fuel is considered part of the empty weight of the aircraft.
Useful load.	The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only.
Utility category.	An airplane that has a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for limited acrobatic operation.
V1.	Critical engine failure speed or takeoff decision speed. It is the speed at which the pilot is to continue the takeoff in the event of an engine failure or other serious emergency. At speeds less than V1, it is considered safer to stop the aircraft within the accelerate-stop distance. It is also the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.
V2.	takeoff safety speed, or a referenced airspeed obtained after lift-off at which the required one engine-inoperative climb performance can be achieved.
VA.	The design maneuvering speed. This is the “rough air” speed and the maximum speed for abrupt maneuvers. If during flight, rough air or severe turbulence is encountered, reduce the airspeed to maneuvering speed or less to minimize stress on the airplane structure. It is important to consider weight when referencing this speed. For example, VA may be 100 knots when an airplane is heavily loaded, but only 90 knots when the load is light.
Vapor lock.	A condition in which air enters the fuel system and it may be difficult, or impossible, to restart the engine. Vapor lock may occur as a result of running a fuel tank completely dry, allowing air to enter the fuel system. On fuel-injected engines, the fuel may become so hot it vaporizes in the fuel line, not allowing fuel to reach the cylinders.
V-bars.	The flight director displays on the attitude indicator that provide control guidance to the pilot.
Vector.	A force vector is a graphic representation of a force and shows both the magnitude and direction of the force.
Velocity.	The speed or rate of movement in a certain direction.
Vertical axis.	An imaginary line passing vertically through the center of gravity of an aircraft. The vertical axis is called the z-axis or the yaw axis.
Vertical card compass.	A magnetic compass that consists of an azimuth on a vertical card, resembling a heading indicator with a fixed miniature airplane to accurately present the heading of the aircraft. The design uses eddy current damping to minimize lead and lag during turns.
Vertical speed indicator (VSI).	An instrument that uses static pressure to display a rate of climb or descent in feet per minute. The VSI can also sometimes be called a vertical velocity indicator (VVI).
Vertical stability.	Stability about an aircraft’s vertical axis. Also called yawing or directional stability.
VFE.	The maximum speed with the flaps extended. The upper limit of the white arc.
VFO.	The maximum speed that the flaps can be extended or retracted.
VFR Terminal Area Charts (1:250,000).	Depict Class B airspace which provides for the control or segregation of all the aircraft within the Class B airspace. The chart depicts topographic information and aeronautical information which includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and related data.
V-G diagram.	A chart that relates velocity to load factor. It is valid only for a specific weight, configuration, and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds.
Visual approach slope indicator (VASI).	The most common visual glidepath system in use. The VASI provides obstruction clearance within 10° of the extended runway centerline, and to 4 nautical miles (NM) from the runway threshold.
Visual Flight Rules (VFR).	Code of Federal Regulations that govern the procedures for conducting flight under visual conditions.
VLE.	Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended.
VLO.	Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear.
VLOF.	Lift-off speed. The speed at which the aircraft departs the runway during takeoff.
VMC.	Minimum control airspeed. This is the minimum flight speed at which a twin-engine airplane can be satisfactorily controlled when an engine suddenly becomes inoperative and the remaining engine is at takeoff power.
VMD.	Minimum drag speed.
VMO.	Maximum operating speed expressed in knots.
VNE.	Never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator.
VNO.	Maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc.
VP.	Minimum dynamic hydroplaning speed. The minimum speed required to start dynamic hydroplaning.
VR.	Rotation speed. The speed that the pilot begins rotating the aircraft prior to lift-off.
VS0.	Stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc.
VS1.	Stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc.
V-speeds.	Designated speeds for a specific flight condition.
VSSE.	Safe, intentional one-engine inoperative speed. The minimum speed to intentionally render the critical engine inoperative.
V-tail.	A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers.
VX.	Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle.
VXSE.	Best angle of climb speed with one engine inoperative. The airspeed at which an airplane gains the greatest amount of altitude in a given distance in a light, twin-engine airplane following an engine failure.
VY.	Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time.
VYSE.	Best rate-of-climb speed with one engine inoperative. This airspeed provides the most altitude gain in a given period of time in a light, twin-engine airplane following an engine failure.
Wake turbulence.	Wingtip vortices that are created when an airplane generates lift. When an airplane generates lift, air spills over the wingtips from the high pressure areas below the wings to the low pressure areas above them. This flow causes rapidly rotating whirlpools of air called wingtip vortices or wake turbulence.
Waste gate.	A controllable valve in the tailpipe of an aircraft reciprocating engine equipped with a turbocharger. The valve is controlled to vary the amount of exhaust gases forced through the turbocharger turbine.
Weathervane.	The tendency of the aircraft to turn into the relative wind.
Weight and balance.	The aircraft is said to be in weight and balance when the gross weight of the aircraft is under the max gross weight, and the center of gravity is within limits and will remain in limits for the duration of the flight.
Weight.	A measure of the heaviness of an object. The force by which a body is attracted toward the center of the earth (or another celestial body) by gravity. Weight is equal to the mass of the body times the local value of gravitational acceleration. One of the four main forces acting on an aircraft. Equivalent to the actual weight of the aircraft. It acts downward through the aircraft’s center of gravity toward the center of the earth. Weight opposes lift.
Wheelbarrowing.	A condition caused when forward yoke or stick pressure during takeoff or landing causes the aircraft to ride on the nose-wheel alone.
Wind correction angle.	Correction applied to the course to establish a heading so that track will coincide with course.
Wind direction indicators.	Indicators that include a wind sock, wind tee, or tetrahedron. Visual reference will determine wind direction and runway in use.
Wind shear.	A sudden, drastic shift in wind speed, direction, or both that may occur in the horizontal or vertical plane.
Windmilling.	When the air moving through a propeller creates the rotational energy.
Windsock.	A truncated cloth cone open at both ends and mounted on a freewheeling pivot that indicates the direction from which the wind is blowing.
Wing area.	The total surface of the wing (square feet), which includes control surfaces and may include wing area covered by the fuselage (main body of the airplane), and engine nacelles.
Wing span.	The maximum distance from wingtip to wingtip.
Wing twist.	A design feature incorporated into some wings to improve aileron control effectiveness at high angles of attack during an approach to a stall.
Wing.	Airfoil attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight.
Wingtip vortices.	The rapidly rotating air that spills over an airplane’s wings during flight. The intensity of the turbulence depends on the airplane’s weight, speed, and configuration. It is also referred to as wake turbulence. Vortices from heavy aircraft may be extremely hazardous to small aircraft.
Yaw string.	A string on the nose or windshield of an aircraft in view of the pilot that indicates any slipping or skidding of the aircraft.
Yaw.	Rotation about the vertical axis of an aircraft.
Zero fuel weight.	The weight of the aircraft to include all useful load except fuel.
Zero sideslip.	A maneuver in a twin-engine airplane with one engine inoperative that involves a small amount of bank and slightly uncoordinated flight to align the fuselage with the direction of travel and minimize drag.
Zero thrust (simulated feather).	An engine configuration with a low power setting that simulates a propeller feathered condition.

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