Glossary of Aviation Terminology |

**XTKD:** Crosstrack deviation

**XTKR:** Crosstrack deviation rate

**XYZ:** A standard aircraft coordinate frame and sign convention, where nose, right wing, and down are positive X, Y, and Z, respectively; often used as subscripts; Compare: east-north-up;

**Yaw:** Angle of heading; Symbols: psi,Psi; Typical Units: rad, deg;

**Yaw rate:** Rate of change of yaw; time derivative of yaw; Symbols: r; Symbols: psi dot; Typical Units: rad/s, deg/s; Dimensions: 1/Time;

**Yoke: **A flight control operated by pushing and pulling with hands in fixed-wing aircraft, primarily to control pitch (altitude) via the elevators; yoke is mounted on a column between the operator's legs, positioned much like a steering wheel in a car; yoke control is achieved by pushing and pulling the wheel to move the column (yoke) fore and aft;

**Yoke cue: **A vertical flight director cue for fixed-wing aircraft, primarily to control altitude, by changing pitch; Compare: collective cue; Symbols: Gamma sub VERT; Typical Units: percent,in;

**Z-plane: **Discrete complex frequency plane; Z-plane is used in control systems engineering in the design of control laws See Also: Z transform;

**Z transform: **A mathematical relationship to model a discrete function in the complex frequency domain (Z-plane); Z transforms are commonly used by systems engineers to describe avionics systems; Compare: continuous-time equation, difference equation, differential equation, discrete-time equation, Laplace transform, state-space model; See Also: first-order filter, second-order filter, unit functions;

**ZOC:** Zone of confusion

**Zone of confusion (ZOC): **A circular area centered at a TACAN station in which bearing is extremely noisy;