Glossary of Aviation Terminology

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Earth coordinates: Coordinates referenced to the earth; See Also: east-north-up; Compare: body coordinates, stability coordinates

Earth data: Environmental data related to the earth at some point of interest; usually a function of latitude and longitude

Earth eccentricity: A measure of the degree to which the earth is oblate; Symbols: epsilon;

Earth model: The earth model computes data related to the earth. Most data is a function of position. Standard models are: International, Clarke 1866, Clarke 1880, Everest, Modified Everest, Bessel 1841, Australian National, World Geodetic Survey 1972, World Geodetic Survey 1984, Airy, Hough, South American.

Earth radius: Radius of the earth, function of position, separate radii for longitudinal radius and for lateral radius; See Also: state data; Symbols: rho; Typical Units: ft; Dimensions: Length;

Earth radius best sphere: Gaussian radius of curvature

Earth radius east/west: Prime radius of curvature

Earth radius north/south: Meridian radius of curvature

Earth-referenced flight path angle: Angle in vertical plane of airspeed vector and groundspeed vector; usual definition for flight path angle; Compare: air-mass flight path angle; Symbols: gamma sub T; Typical Units: rad, deg;

Earthspeed: Total velocity measured with respect to a plane tangent to the earth's surface at the current position; a vector composed of velocity north, velocity east, and vertical velocity; See Also: state data; Symbols: V sub E; Typical Units: kt,ft/s; Dimensions: Length / Time;

East-north-up (ENU): A standard earth coordinate frame and sign convention, where east, north, and up are positive; vertical, or V, is sometimes used in place of up; Synonyms: east-north-vertical; Compare: XYZ;

East-north-vertical (ENV): East-north-up.

ECI: Earth Centered Inertial

Elevation: An angle in the vertical plane through a longitudinal axis; height above mean sea level, usually of terrain;

Elevator: A control surface on fixed-wing aircraft, usually mounted on the aft edge of stabilizers, that controls pitch, and is controlled by the yoke; Symbols: delta sub E; Typical Units: rad, deg;

ENU: East-north-up

ENV: East-north-vertical

Environmental data: Atmospheric data and earth data

Equipment status: Operational status of a piece of equipment consisting of a status indicator and status words; Synonyms: health;

Error: Difference between desired and measured data; Synonyms: delta;

Estimated: Data that is the result of filtering two or more signals; Compare: derived, filtered, measured, raw, selected, smoothed

Euler angles: Pitch, roll, and yaw

Euler parameters: Four parameters for specifiying quaternions; Symbols: e sub < 1 , 2 , 3 , 4 >,a,b,c,s;

Everest: A standard model for computing earth data

Expanding square search: A pattern of progressively larger squares (a ``square spiral'') followed for searching the ground from an aircraft; Compare: creeping line search, sector search;

Extrapolate: Function to determine values from two or values in a table, when the given value lies outside of the range of the table; usually linear but can be higher order;

A , B , C , D , E , F , G , H , I , J - K , L , M , N , O , P , Q - R , S , T , U , V, W, X - Z