Important Aviation Terms

  • AGL – Above Ground Level, as a measurement of altitude above
    a specific land mass, and differentiated from MSL.
  • ADF
    – Automatic Direction Finding via automated radio.
  • ADI
    – Attitude direction indicator. Shows the roll and pitch of the
    aircraft.
  • AFCS – Automatic flight control system that
    provides inputs to the fight controls to assist the pilot in
    maneuvering and handling the aircraft.
  • AFT – Referring
    to the rear of the aircraft.
  • AI – Altitude indicator.
    Displays the aircraft’s altitude above sea level.
  • Aileron
    – The movable areas of a wingform that control or affect the roll of
    an aircraft by working opposite one another-up-aileron on the right
    wing and down-aileron on the left wing.
  • AIM – Airman’s
    Information Manual – A primary FAA publication whose purpose is to
    instruct airmen about operating in the US airspace system.
  • ADC – Air Data Computer – A primary sensor-based navigation
    data source.
  • AGR – Air-Ground Ranging – Straight-line
    distance from the aircraft to a point on the ground.
  • ATC
    – Air Traffic Control – A service operated by the appropriate
    authority to promote the safe, orderly, and expeditious flow of air
    traffic.
  • Airfoil – The shape of the wing when looking
    at its profile. Usually a teardrop shape.
  • Airframe
    The fuselage, booms, nacelles, cowlings, fairings, and airfoil
    surfaces of an aircraft.
  • Airspeed – The speed of an
    aircraft relative to its surrounding air mass. See: calibrated
    airspeed; indicated airspeed; true airspeed.
  • Airspeed
    Indicator
    – An onboard instrument which registers velocity
    through the air, usually in knots. Different from ground speed.
  • AIS – Aeronautical Information Service.
  • ALS
    – Approach light system. A lighting system installed on the approach
    end of an airport runway and consists of a series of lightbars,
    strobe lights, or a combination of the two that extends outward from
    the runway end.
  • ALT – Short term for Altitude.
  • Altimeter – An onboard instrument which senses air pressure
    in order to gauge altitude.
  • Altimeter Setting – The
    barometric pressure reading used to adjust a pressure altimeter for
    variations in existing atmospheric pressure.
  • Altitude
    – Height of an aircraft, usually with respect to the terrain below.
  • Angle of Attack – The angle between the chord line of the
    wing of an aircraft and the relative wind.
  • Annual
    Mandatory inspection of airframe and power plant that occurs every
    12 months.
  • AO – Aircraft Operator.
  • AOPA
    – Aircraft Owner and Pilot’s Association.
  • APP
    Approach (Control).
  • Approach Speed – The recommended
    speed contained in aircraft manuals used by pilots when making an
    approach to landing.
  • ARCID – Aircraft Identification.
  • ATA – Actual Time of Arrival. As opposed to ETA
    (Estimated Time of Arrival) used in filing a flight plan.

  • ATD
    – Actual Time of Departure. As opposed to ETD (Estimated
    Time of Departure) used in filing a flight plan.
  • ATIS – Automated Terminal Information
    Service usually containing vital information on wind
    direction, velocity, pressure readings, and active runway
    assignment for that particular airport.
  • Attitude
    – The primary aircraft angles in the state vector; pitch,
    roll, and yaw.
  • Attitude Indicator – A vacuum
    powered instrument which displays pitch and roll movement
    about the lateral and longitudinal axes.
  • ADF
    Automatic Direction Finding – A basic guidance mode,
    providing lateral guidance to a radio station. Equipment
    that determines bearing to a radio station.

  • Autopilot
    – A method of an automatic flight control
    system which controls primary flight controls to meet
    specific mission requirements.
  • Autorotation
    A rotorcraft flight condition in which the lifting rotor is
    driven entirely by action of the air when the rotorcraft is
    in motion.
  • AVGAS – Aviation Gasoline (piston aircraft fuel).
  • Bernoulli Effect – Airflow over the upper surface of an
    airfoil causes suction (lift) because the airstream has been speeded
    up in relation to positive pressure of the airflow on the lower
    surface.
  • CAS – Calibrated Airspeed – The indicated
    airspeed of an aircraft, corrected for position and instrument
    error. CAS is equal to true airspeed in standard atmosphere at sea
    level.
  • Camber – The convex or concave curvature of an
    airfoil.
  • CAT – Clear Air Turbulance.
  • CAVU
    – Ceiling and Visibility Unlimited; ideal flying weather.

  • Ceiling
    – The heights above the earth’s surface of the lowest
    layer of clouds or obscuring phenomena that is reported as “broken,”
    “overcast,” or “obscured”.
  • CG – Center of Gravity
    The longitudinal and lateral point in an aircraft where it is
    stable; the static balance point.
  • Chord – The
    measurable distance between the leading and trailing edges of a
    wingform.
  • CTAF – Common Traffic Advisory Frequency – A
    frequency designed for the purpose of carrying out airport advisory
    practices while operating to or from an airport without an operating
    control tower. The CTAF may be a UNICOM, Multicom, FSS, or tower
    frequency and is identified in appropriate aeronautical
    publications.
  • Controlled Airspace – An airspace of
    defined dimensions within which air traffic control service is
    provided to IFR flights and to VFR flights in accordance with the
    airspace classification. Controlled airspace is a generic term that
    covers Class A, B, C, D, and E airspace.
  • Crabbing – A
    rudder-controlled yawing motion to compensate for a crosswind in
    maintaining a desired flight path, as in a landing approach.
  • Dead Reckoning – The process of estimating one’s current
    position based upon a previously determined position, or fix, and
    advancing that position based upon known speed, elapsed time, and
    course.
  • Deadstick – Descending flight with engine and
    propeller stopped.
  • Departure Stall – A stall in the
    takeoff configuration with power.
  • Deviation (Magnetic)
    – The error of a Magnetic Compass due to inherent magnetic
    influences in the structure and equipment of an aircraft.

  • Directional Gyro
    – A panel instrument providing a gyroscopic
    reading of an aircraft’s compass heading.
  • DME
    Distance Measuring Equipment, a radio navigation device that
    determines an aircraft’s distance from a given ground station, as
    well as its groundspeed and time to/from the station.
  • Drag
    – The resisting force exerted on an aircraft in its line of flight
    opposite in direction to its motion.
  • Dry Weight – The
    weight of an engine exclusive of any fuel, oil, and coolant.
  • Elevator – The movable part of a horizontal airfoil which
    controls the pitch of an aircraft, the fixed part being the
    Stabilzer.
  • ETA – Estimated time of arrival.

  • ETD
    – Estimated time of departure.
  • FBO
    Fixed-Base Operator. A commercial operator supplying fuel,
    maintenance, flight training, and other services at an airport.
  • FAR – Federal Air Regulations.
  • Flap – A
    movable, usually hinged airfoil set in the trailing edge of an
    aircraft wing, designed to increase lift or drag by changing the
    camber of the wing or used to slow an aircraft during landing by
    increasing lift.
  • Flare – A control wheel maneuver
    performed moments before landing in which the nose of an aircraft is
    pitched up to minimize the touchdown rate of speed.
  • Flight
    Envelope
    – An aircraft’s performance limits, specifically the
    curves of speed plotted against other variables to indicate the
    limits of speed, altitude, and acceleration that a particular
    aircraft cannot safely exceed.
  • Flight Plan – Specified
    information relating to the intended flight of an aircraft, filed
    orally or in writing with an FSS or an ATC facility.
  • FSS –
    Flight Service Station
    – Air traffic facilities which provide
    pilot briefing, enroute communications and VFR search and rescue
    services, and assist lost aircraft.
  • Fuselage – An
    aircraft’s main body structure housing the flight crew, passengers,
    and cargo and to which the wings, tail and, in most single-engined
    airplanes, engine are attached.
  • GA – General Aviation
    – That portion of civil aviation which encompasses all facets of
    aviation except air carriers holding a certificate of public
    convenience and necessity from the Civil Aeronautics Board and large
    aircraft commercial operators.
  • Glass Cockpit – Said of
    an aircraft’s control cabin which has all-electronic, digital and
    computer-based, instrumentation.
  • Glider – An unpowered
    aircraft capable of maintaining altitude only briefly after release
    from tow, then gliding to earth.
  • Glide Scope – (1) The
    angle between horizontal and the glide path of an aircraft. (2) A
    tightly-focused radio beam transmitted from the approach end of a
    runway indicating the minimum approach angle that will clear all
    obstacles; one component of an instrument landing system (ILS).
  • GPS – Global Positioning System; satellite-based
    navigation, rapidly replacing dead reckoning methods.

  • Gross Weight
    – The total weight of an aircraft when fully
    loaded, including fuel, cargo, and passengers; aka Takeoff Weight.
  • Ground Control – Tower control, by radioed instructions
    from air traffic control, of aircraft ground movements at an
    airport.
  • Ground Effect – Increased lift generated by
    the interaction between a lift system and the ground when an
    aircraft is within a wingspan distance above the ground. It affects
    a low-winged aircraft more than a mid- or high-winged aircraft
    because its wings are closer to the ground.
  • Ground Speed
    – The actual speed that an aircraft travels over the ground its
    “shadow speed”; it combines the aircraft’s airspeed and the wind’s
    speed relative to the aircraft’s direction of flight.
  • IFR
    – Instrument Flight Rules, governing flight under instrument
    meteorological conditions.
  • ILS – Instrument Landing
    System. A radar-based system allowing ILS-equipped aircraft to find
    a runway and land when clouds may be as low as 200′ (or lower for
    special circumstances).
  • IAS – Indicated Air Speed – A
    direct instrument reading obtained from an air speed indicator
    uncorrected for altitude, temperature, atmospheric density, or
    instrument error. Compare calibrated airspeed and true airspeed.
  • IMC – Instrument Meterological Conditions –
    Meteorological conditions expressed in terms of visibility, distance
    from clouds, and ceiling less than minimal specified for visual
    meteorological conditions (VMC).
  • Knot – One nautical
    mile, about 1.15 statute miles (6,080′); eg: 125kts = 143.9mph.
  • Lift – The force exerted on the top of a moving airfoil
    as a low-pressure area [vacuum] that causes a wingform to rise.
    airfoils do not “float” on air, as is often assumed – like a boat
    hull floats on water – but are “pulled up” (lifted) by low air
    pressures trying to equalize.
  • Lift-Drag Ratio – The
    lift coefficient of a wing divided by the drag coefficient, as the
    primary measure of the efficiency of an aircraft; aka L/D ratio.
  • Liquid Compass – A non-electronic, calibratable compass
    floating in a liquid as a panel instrument; aka wet compass.
  • Load Factor – The proportion between lift and weight commonly
    seen as g (sometimes capitalized) – a unit of force equal to the
    force of gravity times one.
  • LORAN – Long Range Navigation
    System
    – Utilizes timing differences between multiple
    low-frequency transmissions to provide accurate latitude/longitude
    position information to within 50′.
  • LTA
    Lighter-than-air craft, generally referring to powered blimps and
    dirigibles, but often also includes free balloons.

  • Magnetic Compass
    – The most common liquid-type compass, capable
    of calibration to compensate for magnetic influences within the
    aircraft.
  • Magnetic Course – Compass course + or –
    deviation.
  • Magnetic North – The magnetic North pole,
    located near 71° North latitude and 96° West longitude, that
    attracts a magnetic compass which is not influenced by local
    magnetic attraction.
  • MAG – Magneto – An accessory that
    produces and distributes a high-voltage electric current for
    ignition of a fuel charge in an internal combustion engine.
  • MSL – Mean Sea Level. The average height off the surface of
    the sea for all stages of tide; used as a reference for elevations,
    and differentiated from AGL.
  • METAR – Acronym in FAA
    pilot briefings and weather reports simply means an “aviation
    routine weather report”.
  • NDB – Non Directional Beacon
    – An LF, MF, or UHF radio beacon transmitting non-directional
    signals whereby the pilot of an aircraft equipped with direction
    finding equipment can determine his bearing to or from the radio
    beacon and “home” on or track to or from the station.
  • PAR
    – Precision Approach Radar, a ground-radar-based instrument approach
    providing both horizontal and vertical guidance.
  • Pattern
    – The path of aircraft traffic around an airfield, at an established
    height and direction. At tower-controlled fields the pattern is
    supervised by radio (or, in non-radio or emergency conditions by red
    and green light signals) by air traffic controllers. Flying an
    entire pattern is called a ‘Circuit’.
  • PIC – Pilot in
    Command
    – The pilot responsible for the operation and safety of
    an aircraft during flight time.
  • Pitch – Of the three
    axes in flight, this specifies the vertical action, the up-and-down
    movement.
  • Pitot Tube – More accurately but less
    popularly used, Pitot-Static Tube, a small tube most often mounted
    on the outward leading edge of an airplane wing (out of the
    propeller stream) that measures the impact pressure of the air it
    meets in flight, working in conjuction with a closed, perforated,
    coaxial tube that measures the static pressure.
  • Roll
    Of the three axes in flight, this specifies the action around a
    central point.
  • Rotorcraft – A heavier-than-air
    aircraft that depends principally for its support in flight on the
    lift generated by one or more rotors. Includes helicopters and
    gyroplanes.
  • Rudder – The movable part of a vertical
    airfoil which controls the YAW of an aircraft; the fixed part being
    the fin.
  • Scud – A low, foglike cloud layer.

  • Service Ceiling
    – The height above sea level at which an
    aircraft with normal rated load is unable to climb faster than 100′
    per minute under Standard Air conditions.
  • Sideslip – A
    movement of an aircraft in which a relative flow of air moves along
    the lateral axis, resulting in a sideways movement from a projected
    flight path, especially a downward slip toward the inside of a
    banked turn.
  • Sink, Sinking Speed – The speed at which
    an aircraft loses altitude, especially in a glide in still air under
    given conditions of equilibrium.
  • Skid – Too shallow a
    bank in a turn, causing an aircraft to slide outward from its ideal
    turning path.
  • Slip – Too steep a bank in a turn,
    causing an aircraft to slide inward from its ideal turning path.
  • Slipstream – The flow of air driven backward by a
    propeller or downward by a rotor.
  • Squawk Code – A
    four-digit number dialed into his transponder by a pilot to identify
    his aircraft to air traffic controllers.
  • Stabilizer
    The fixed part of a horizontal airfoil that controls the pitch of an
    aircraft; the movable part being the elevator.
  • Stall
    (1) Sudden loss of lift when the angle of attack increases to a
    point where the flow of air breaks away from a wing or airfoil,
    causing it to drop. (2) A maneuver initiated by the steep raising of
    an aircraft’s nose, resulting in a loss of velocity and an abrupt
    drop.
  • TAS – True Air Speed – True Air Speed. Because
    an air speed indicator indicates true air speed only under standard
    sea-level conditions, true air speed is usually calculated by
    adjusting an Indicated Air speed according to temperature, density,
    and pressure.
  • Thrust – The driving force of a
    propeller in the line of its shaft or the forward force produced in
    reaction to the gases expelled rearward from a jet or rocket engine.
    Opposite of drag.
  • Torque – A twisting, gyroscopic
    force acting in opposition to an axis of rotation, such as with a
    turning propeller; aka Torsion.
  • Touch-and-Go – Landing
    practice in which an aircraft does not make a full stop after a
    landing, but proceeds immediately to another take-off.

  • Transponder
    – An airborne transmitter that responds to
    ground-based interrogation signals to provide air traffic
    controllers with more accurate and reliable position information
    than would be possible with “passive” radar; may also provide air
    traffic control with an aircraft’s altitude.
  • Trim Tab
    – A small, auxiliary control surface in the trailing edge of a
    wingform, adjustable mechanically or by hand, to counteract (“trim”)
    aerodynamic forces on the main control surfaces.
  • Turn &
    Bank Indicator
    – Primary air-driven gyro instrument, a combined
    turn indicator and lateral inclinometer to show forces on an
    aircraft in banking turns. Also referred to as “needle & ball”
    indicator, the needle as the gyro’s pointer and a ball encased in a
    liquid-filled, curved tube.
  • Uncontrolled Airspace
    Class G Airspace; airspace not designated as Class A, B, C, D or E.
  • UNICOM – Universal Communication – A common radio
    frequency (usually 121.0 mHz) used at uncontrolled (non-tower)
    airports for local pilot communication.
  • Useful Load
    The weight of crew, passengers, fuel, baggage, and ballast,
    generally excluding emergency or portable equipment and ordnance.
  • V– Velocity – Used in defining air speeds, listed below:VA = Maneuvering Speed (max structural speed for full
    control deflection)
    VD = Max Dive Speed (for
    certification only)
    VFE = Max Flaps Extended Speed
    VLE
    = Max Landing Gear Extended Speed
    VLO = Max Landing Gear
    Operation Speed
    VNE = Never Exceed Speed
    VNO
    = Max Structural Cruising Speed
    VS0 = Stalling Speed
    Landing Configuration
    VS1 = Stalling Speed in a
    specified Configuration
    VX = Best Angle of Climb Speed

    VXSE = Best Angle of Climb Speed, one engine out
    VY
    = Best Rate of Climb Speed
    VYSE = Best Rate of Climb
    Speed, one engine out

  • VASI – Visual Approach Slope
    Indicator – A system of lights on the side of an airport runway that
    provides visual descent guidance information during the approach to
    a runway.
  • Venturi Tube – A small, hourglass-shaped
    metal tube, usually set laterally on a fuselage in the slipstream to
    create suction for gyroscopic panel instruments. Now outdated by
    more sophisticated means.
  • VFR – Visual Flight Rules
    that govern the procedures for conducting flight under visual
    conditions. The term is also used in the US to indicate weather
    conditions that are equal to or greater than minimum VFR
    requirements. Also used by pilots and controllers to indicate a
    specific type of flight plan.
  • VMC – Visual
    Meteorological Conditions – Expressed in terms of visibility,
    distance from clouds, and ceiling equal to or better than specified
    minima.
  • VOR – VHF OmniRange – A ground-based
    navigation aid transmitting very high-frequency (VHF) navigation
    signals 360° in azimuth, on radials oriented from magnetic nort. The
    VOR periodically identifies itself by Morse Code and may have an
    additional voice identification feature. Voice features can be used
    by ATC or FSS for transmitting information to pilots.
  • VSI
    – Vertical Speed Indicator. A panel instrument that gauges rate of
    climb or descent in feet-per-minute (fpm). Also called the Rate Of
    Climb Indicator.
  • Yaw – Of the three axes in flight,
    this specifies the side-to-side movement of an aircraft on its
    vertical axis, as in skewing.
  • Yoke – The control wheel
    of an aircraft, akin to a automobile steering wheel.