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. G-5