Cone of confusion. A cone-shaped volume of airspace directly above a VOR station where no signal is received, causing the CDI to fluctuate. 

Control and performance.  A method of attitude instrument flying in which one instrument is used for making attitude changes, and the other instruments are used to monitor the progress of the change. 

Control display unit. A display interfaced with the master computer, providing the pilot with a single control point for all navigations systems, thereby reducing the number of required flight deck panels. 

Controlled airspace. An airspace of defined dimensions within which ATC service is provided to IFR and VFR flights in accordance with the airspace classification. It includes Class A, Class B, Class C, Class D, and Class E airspace. 

Control pressures.  The amount of physical exertion on the control column necessary to achieve the desired attitude. 

Convective weather. Unstable, rising air found in cumiliform clouds. 

Convective SIGMET. Weather advisory concerning convective weather significant to the safety of all aircraft, including thunderstorms, hail, and tornadoes. 

Coordinated flight.  Flight with a minimum disturbance of the forces maintaining equilibrium, established via effective control use. 

COP.  See changeover point. 

Coriolis illusion.  The illusion of rotation or movement in an entirely different axis, caused by an abrupt head movement, while in a prolonged constant rate turn that has ceased stimulating the brain’s motion sensing system. 

Crew resource management (CRM). The effective use of all available resources—human, hardware, and information. 

Critical areas.  Areas where disturbances to the ILS localizer and glide slope courses may occur when surface vehicles or aircraft operate near the localizer or glide slope antennas. 

CRM.  See crew resource management. 

Cross-check.  The first fundamental skill of instrument flight, also known as “scan,” the continuous and logical observation of instruments for attitude and performance information. 

Cruise clearance. An ATC clearance issued to allow a pilot to conduct flight at any altitude from the minimum IFR altitude up to and including the altitude specified in the clearance. Also authorizes a pilot to proceed to and make an approach at the destination airport. 

Current induction.  An electrical current being induced into, or generated in, any conductor that is crossed by lines of flux from any magnet. 

DA.  See decision altitude. 

D.C.  Direct current. 

Dark adaptation.  Physical and chemical adjustments of the eye that make vision possible in relative darkness. 

Deceleration error.  A magnetic compass error that occurs when the aircraft decelerates while flying on an easterly or westerly heading, causing the compass card to rotate toward South. 

Decision altitude (DA).  A specified altitude in the precision approach, charted in feet MSL, at which a missed approach must be initiated if the required visual reference to continue the approach has not been established. 

Decision height (DH).  A specified altitude in the precision approach, charted in height above threshold elevation, at which a decision must be made either to continue the approach or to execute a missed approach. 

Deice. The act of removing ice accumulation from an aircraft structure. 

Density altitude.  Pressure altitude corrected for nonstandard temperature. Density altitude is used in computing the performance of an aircraft and its engines. 

Departure procedure (DP).  Preplanned IFR ATC departure, published for pilot use, in textual and graphic format. 

Deviation. A magnetic compass error caused by local magnetic fields within the aircraft. Deviation error is different on each heading. 

DGPS.  Differential global positioning system. 

DH.  See decision height. 

