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.
