Glossary of Aviation Terminology |

**Calibrated airspeed (CAS):** Indicated airspeed corrected for instrumentation errors, but not for air density; See Also: airspeed; Symbols: V sub 'CAS'; Typical Units: kt,ft/s; Dimensions: Length / Time;

**Calibration:** A basic control to a data source from controls and displays for calibrating a device; Also, a procedure to adjust physical devices so that they provide the most accurate results possible; calibration procedures commonly result in correction factors to be downloaded from the host processor to the device; during calibration, the device is usually not available; See Also: alignment, boresighting, initialization;

**Cant angle:** Angle of nacelle mounting; Typical Units: rad, deg;

**Capture: **To attain an objective, such as reaching a radial of a radio station; See Also: capture criterion; Compare: activate, arm;

**Capture criterion:** A test case to determine if an armed objective has been captured; In avionics, an aircraft might have an objective to fly to a radial of a radio station, then to fly along it. While enroute, the objective is armed, meaning that the crew and software are attempting to reach the radial. The radial is captured and the objective is met when the capture criteria are met. In this case, the capture criterion might be bearing to the radio station is within 5deg of 270deg. An objective can have multiple criteria. Capture criterion are often used with radio navigation to determine a transition from armed to active.

**CAS: **Calibrated airspeed

**Caution: **A signal which alerts the operator to an impending dangerous condition requiring attention, but not necessarily immediate action (from MIL-STD-1472D); an annunciator that is more critical than an advisory but less critical than a warning;

**CCLIM:** Course cut limit

**Center line:** Standard aviation term

**CEP: **Circular error probability

**Channel:** A number that maps to a frequency;

**Circular error probability (CEP): **A probability that a percentage of two-dimension measurements will lie within a circle of given radius, with the circle centered at truth or mean of the measurements; Compare: radial error probability, spherical error probability; CEP specifies test cases for measurement errors of sensors of two dimensions, such as velocity east and north.

**Clarke 1866:** A standard model for computing earth data

**Clarke 1880: **A standard model for computing earth data

**Collective: **A flight control operated by moving up or down with hand in rotary-wing aircraft, primarily to control lift (altitude); controls collective (total) pitch of the rotors on a rotary-wing aircraft;

**Collective cue:** A vertical flight director cue for rotary-wing aircraft, primarily to control altitude, by changing power; Compare: yoke cue; Symbols: Gamma sub 'VERT'; Typical Units: percent,in;

**Commanded:** Controls given to a device, not that the device necessarily obeyed the controls

**Communications: **How well equipment is communicating; Values: operational, degraded, failed

**Complementary filter:** A filter in which the complement of the filter is desired, giving the effect of a high-pass filter by implementing a low-pass filter; a filter for combining multiple data sources, usually of different types, by adding filtered values, where the sum of the filters in the frequency domain is unity; a Kalman filter with fixed gains; Complementary filters are often designed in the frequency domain in way that that the filters determined at build time such that the cutoff frequency of the LFP is equal to that of the HPF. This provides the advantages of DNS's long-term accuracy and INS's short-term accuracy, while filtering DNS's high-frequency noise and INS's slow drift. Compare: averaging filter, Kalman filter;

**Computer cycle: **In a periodic, cyclical computer system, the most basic, fastest timing loop

**Continuous time: **Time which can have any point expressed as a real quantity, without regard for any specific interval or processing rate; Compare: discrete time;

**Continuous-time equation:** A mathematical relationship to describe a function of time, expressed in terms of continuous time; Compare: difference equation, differential equation, discrete-time equation, Laplace transform, state-space model, Z transform; See Also: first-order filter, second-order filter, unit functions for examples;

**Control law: **The mathematical definition of a system used to control or to change the dynamic response of a system;

**Control surface: **An airfoil attached to an aircraft that is moved to control the attitude of the aircraft; an surface to control flight of an aircraft indirectly, such as a swashplate to control pitch of rotor blades; See Also: aileron, rudder, spoiler, elevator, flaps, trim tab, stabilizer; Symbols: delta; Typical Units: rad, deg;

**Controlled altitude (CTALT):** A guidance control law parameter, generated by the vertical guidance modes; altitude that is being controlled Typical Units: ft; Dimensions: Length;

**Controlled speed (CTS):** A guidance control law parameter, generated by the longitudinal guidance modes; speed that is being controlled Typical Units: ft/s, kt; Dimensions: Length / Time;

**Coriolis acceleration: **Tangential acceleration caused by motion on a radial on a rotating surface, in aviation, it is acceleration in the earth's longitudinal direction caused by changing latitude, usually computed from system state data; Symbols: a sub c; Typical Units: ft/s-squared,g; Dimensions: Length / Time-squared;

**Corrected altitude: **Measured pressure altitude corrected for instrumentation errors

**Coupled:** Describes operation of flight director in which automatic flight control system causes flight controls to follow commands from flight director or errors from guidance

**Course: **Towards a point at a specified course; Compare: direct

**Course cut limit (CCLIM): **A guidance control law parameter, generated by the lateral guidance modes; limits the intercept angle of the flight path with a desired course, typically 45deg Typical Units: deg, rad;

**Creeping line search: **A pattern of equally spaced parallel lines followed for searching the ground from an aircraft; Compare: expanding square search, sector search;

**Cross track:** Perpendicular to the course;

**Crosstrack deviation (XTKD): **A guidance control law parameter, generated by the lateral guidance modes; distance from the aircraft to a desired course measured along a prependicular to the course Typical Units: ft; Dimensions: Length;

**Crosstrack deviation gain (KXTKD): **A guidance control law parameter, generated by the lateral guidance modes; relative weighting of crosstrack deviation in the lateral control law Typical Units: rad/ft; Dimensions: 1/L;

**Crosstrack deviation rate (XTKR): **A guidance control law parameter, generated by the lateral guidance modes; rate of change of crosstrack deviation Typical Units: ft/s; Dimensions: Length / Time;

**Crosstrack deviation rate gain (KXTKR): **A guidance control law parameter, generated by the lateral guidance modes; relative weighting of the crosstrack deviation rate in the lateral control law Typical Units: s; Dimensions: Time;

**CTALT:** Controlled altitude

**CTS: **Controlled speed

**Cue:** A indicator to an operator for control placement, tells the operator where to place controls; Synonyms: command

**Cursor:** See: moding cursor, target cursor

**Cutoff frequency: **The frequency at which the gain of a filter is at an edge of a band, usually taken to be when gain is 0.5, or -3.01dB; the frequency at which the output of a filter is half the power of the input; See Also: band-pass filter, high-pass filter, low-pass filter; Symbols: omega sub c; Typical Units: rad/s,Hz; Dimensions: 1/Time;

**Cyclic:** See: longitudinal cyclic, lateral cyclic;