Class C Airspace.  Airspace from the surface to 4,000 feet above the airport elevation (charted in MSL) surrounding those airports having an operational control tower, serviced by radar approach control, and having a certain number of IFR operations or passenger numbers. Although the configuration of each Class C airspace area is individually tailored, the airspace usually consists of a 5 NM radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends from 1,200 feet to 4,000 feet above the airport elevation. 

Class D Airspace. Airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower. The configuration of each Class D airspace area is individually tailored, and when instrument procedures are published, the airspace will normally be designed to contain the procedures. 

Class E Airspace. Airspace that is not Class A, Class B, Class C, or Class D, and is controlled airspace. 

Class G Airspace.  Airspace that is uncontrolled, except when associated with a temporary control tower, and has not been designated as Class A, Class B, Class C, Class D, or Class E airspace. 

Clear air turbulence.  Turbulence not associated with any visible moisture. 

Clearance. ATC permission for an aircraft to proceed under specified traffic conditions within controlled airspace, for the purpose of providing separation between known aircraft. 

Code of Federal Regulations (CFR). Regulations issued by the U.S. Federal Government as published in the Federal Register. 

Coefficient of lift (C$_{L}$).  The ratio between lift pressure and dynamic pressure. 

Cold front. The boundary between two air masses where cold air is replacing warm air. 

Combustion.  Process of burning the fuel/air mixture in the engine in a controlled and predictable manner. 

Combustion chamber.  The section of the engine into which fuel is injected and burned. 

Common Traffic Advisory Frequency (CTAF).  A frequency designed for the purpose of carrying out airport advisory practices while operating to or from an airport 

without an operating control tower. The CTAF may be a UNICOM, Multicom, automated flight service station, or tower frequency and is identified in appropriate aeronautical publications. 

Controlled airspace.  An airspace of defined dimensions within which air traffic control service is provided to IFR flights and to VFR flights in accordance with the airspace classification. Note: “controlled airspace” is a generic term that encompasses Class A, Class B, Class C, Class D, and Class E airspace. 

Control bar. The structural part of the wing that connects the flying wires the the wing and keel. This is also used for the pilot to control the WSC pitch and roll in flight. 

Control frame.  The wing structural triangle which connects the control bar to the wing keel and provides the structure for the lower flying wire attachments. 

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

Control tower.  A terminal facility that uses air/ground communications, visual signaling, and other devices to provide ATC services to aircraft operating in the vicinity of an airport or on the movement area. Authorizes aircraft to land or takeoff at the airport controlled by the tower or to transit the Class D airspace area regardless of the flight plan or weather conditions. May also provide approach control services (radar or nonradar). 

Controllability. A measure of the response of an aircraft relative to the pilot’s flight control inputs. 

Course.  The intended direction of flight in the horizontal plane measured in degrees from north. 

Coordinated turn.  Turn made by an aircraft where the horizontal component of lift is equal to the centrifugal force of the turn. 

Crab angle.  The angle formed between the direction an aircraft is pointed and the direction it is tracking over the ground, resulting from a crosswind component. Also called the wind correction angle. 

Crewmember. A person assigned to perform duty in an aircraft during flight time. 

Crew resource management (CRM).  The application of team management concepts in the flight deck environment, including single pilots of general aviation aircraft. Pilots of small aircraft, as well as crews of larger aircraft, must make 

