Glossary

Class A airspace. Airspace from 18,000 feet MSL up to and Clearance delivery. Control tower position responsible for including FL 600, including the airspace overlying the waters transmitting departure clearances to IFR flights. within 12 NM of the coast of the 48 contiguous states and Alaska; and designated international airspace beyond 12 NM Clearance limit. The fix, point, or location to which an of the coast of the 48 contiguous states and Alaska within areas aircraft is cleared when issued an air traffic clearance. of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied. Clearance on request. An IFR clearance not yet received after filing a flight plan. Class B airspace. Airspace from the surface to 10,000 feet MSL surrounding the nation’s busiest airports in terms of Clearance void time. Used by ATC, the time at which the IFR operations or passenger numbers. The configuration of departure clearance is automatically canceled if takeoff has each Class B airspace is individually tailored and consists not been made. The pilot must obtain a new clearance or of a surface area and two or more layers, and is designed to cancel the IFR flight plan if not off by the specified time. contain all published instrument procedures once an aircraft enters the airspace. For all aircraft, an ATC clearance is Clear ice. Glossy, clear, or translucent ice formed by the required to operate in the area, and aircraft so cleared receive relatively slow freezing of large, supercooled water droplets. separation services within the airspace. Coefficient of lift (C ). The ratio between lift pressure and L Class C airspace. Airspace from the surface to 4,000 feet dynamic pressure. above the airport elevation (charted in MSL) surrounding those airports having an operational control tower, serviced Cold front. The boundary between two air masses where by radar approach control, and having a certain number of IFR cold air is replacing warm air. operations or passenger numbers. Although the configuration of each Class C airspace area is individually tailored, the Compass course. A true course corrected for variation and airspace usually consists of a 5 NM radius core surface area deviation errors. that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends from Compass locator. A low-power, low- or medium-frequency 1,200 feet to 4,000 feet above the airport elevation. (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS. Class D airspace. Airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding Compass rose. A small circle graduated in 360° increments, those airports that have an operational control tower. The to show direction expressed in degrees. configuration of each Class D airspace area is individually tailored, and when instrument procedures are published, the Complex aircraft. An aircraft with retractable landing gear, airspace is normally designed to contain the procedures. flaps, and a controllable-pitch propeller. Class E airspace. Airspace that is not Class A, Class B, Class Compressor pressure ratio. The ratio of compressor C, or Class D, and is controlled airspace. discharge pressure to compressor inlet pressure. Class G airspace. Airspace that is uncontrolled, except Compressor stall. In gas turbine engines, a condition in when associated with a temporary control tower, and has an axial-flow compressor in which one or more stages of not been designated as Class A, Class B, Class C, Class D, rotor blades fail to pass air smoothly to the succeeding or Class E airspace. stages. A stall condition is caused by a pressure ratio that is incompatible with the engine rpm. Compressor stall will be Clean configuration. A configuration in which all flight indicated by a rise in exhaust temperature or rpm fluctuation, control surfaces have been placed to create minimum drag. and if allowed to continue, may result in flameout and In most aircraft this means flaps and gear retracted. physical damage to the engine. Clearance. ATC permission for an aircraft to proceed under Computer navigation fix. A point used to define a specified traffic conditions within controlled airspace, for navigation track for an airborne computer system such as the purpose of providing separation between known aircraft. GPS or FMS. G-7