Aeronautical Terms beginning with C

Controlled Flight Into Terrain (CFIT)

A situation where a mechanically normally functioning airplane is inadvertently flown into the ground, water, or an obstacle. There are two basic causes of CFIT accidents; both involve flight crew situational awareness. One definition of situational awareness is an accurate perception by pilots of the factors and conditions currently affecting the safe operation of the aircraft and the crew. The causes of CFIT are the flight crews lack of vertical position awareness or their lack of horizontal position awareness in relation to terrain and obstacles.


Center Radar ARTS Presentation/Processing (CENRAP)

CENRAP was developed to provide an alternative to a non-radar environment at terminal facilities should an ASR fail or malfunction. CENRAP sends aircraft radar beacon target information to the ASR terminal facility equipped with ARTS.


Changeover Point (COP)

A COP indicates the point where a frequency change is necessary between navigation aids when other than the midpoint on an airway, to receive course guidance from the facility ahead of the aircraft instead of the one behind. These COPs divide an airway or route segment and ensure continuous reception of navigational signals at the prescribed minimum en route IFR altitude.


Charted Visual Flight Procedure (CVFP)

A CVFP may be established at some towered airports for environmental or noise considerations, as well as when necessary for the safety and efficiency of air traffic operations. Designed primarily for turbojet aircraft, CVFPs depict prominent landmarks, courses, and recommended altitudes to specific runways.


Cockpit display of traffic information (CDTI)

The display and user interface for information about air traffic within approximately 80 miles. It will typically combine and show traffic data from TCAS, TIS-B, and ADS-B. Depending on features, the display may also show terrain, weather, and navigation information.


Collision Hazard

A condition, event, or circumstance that could induce an occurrence of a collision or surface accident or incident.


Columns

See Database Columns


Contact Approach

An approach where an aircraft on an IFR flight plan, having an air traffic control authorization, operating clear of clouds with at least one mile flight visibility, and a reasonable expectation of continuing to the destination airport in those conditions, may deviate from the instrument approach procedure and proceed to the destination airport by visual reference to the surface. This approach will only be authorized when requested by the pilot and the reported ground visibility at the destination airport is at least one statute mile.


Cabin Pressurization

A condition where pressurized air is forced into the cabin simulating pressure conditions at a much lower altitude and increasing the aircraft occupants comfort.


Calibrated Airspeed (CAS)

Indicated airspeed corrected for installation error and instrument error. Although manufacturers attempt to keep airspeed errors to a minimum, it is not possible to eliminate all errors throughout the airspeed operating range. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots. This error is generally greatest at low airspeeds. In the cruising and higher airspeed ranges, indicated airspeed and calibrated airspeed are approximately the same. Refer to the airspeed calibration chart to correct for possible airspeed errors.


Cambered

The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.


Carburetor

1. Pressure: A hydromechanical device employing a closed feed system from the fuel pump to the discharge nozzle. It meters fuel through fixed jets according to the mass airflow through the throttle body and discharges it under a positive pressure. Pressure carburetors are distinctly different from float-type carburetors, as they do not incorporate a vented float chamber or suction pickup from a discharge nozzle located in the venturi tube. 2. Float-type: Consists essentially of a main air passage through which the engine draws its supply of air, a mechanism to control the quantity of fuel discharged in relation to the flow of air, and a means of regulating the quantity of fuel/air mixture delivered to the engine cylinders.


Carburetor Ice

Ice that forms inside the carburetor due to the temperature drop caused by the vaporization of the fuel. Induction system icing is an operational hazard because it can cut off the flow of the fuel/air charge or vary the fuel/air ratio.


Cascade Reverser

A thrust reverser normally found on turbofan engines in which a blocker door and a series of cascade vanes are used to redirect exhaust gases in a forward direction.


Center Of Gravity(CG)

The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percent of mean aerodynamic chord (MAC). The location depends on the distribution of weight in the airplane.


Center-Of-Gravity Limits

The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.


Center-Of-Gravity Range

The distance between the forward and aft CG limits indicated on pertinent airplane specifications.


Centrifugal Flow Compressor

An impeller-shaped device that receives air at its center and slings air outward at high velocity into a diffuser for increased pressure. Also referred to as a radial outflow compressor.


Chord Line

An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.


Circuit Breaker

A circuit-protecting device that opens the circuit in case of excess current flow. A circuit breakers differs from a fuse in that it can be reset without having to be replaced.


Clear Air Turbulence

Turbulence not associated with any visible moisture.


Climb Gradient

The ratio between distance traveled and altitude gained.


Cockpit Resource Management

Techniques designed to reduce pilot errors and manage errors that do occur utilizing cockpit human resources. The assumption is that errors are going to happen in a complex system with error-prone humans.


Coefficient Of Lift

See Lift Coefficient.


Coffin Corner

The flight regime where any increase in airspeed will induce high speed mach buffet and any decrease in airspeed will induce low speed mach buffet.


Combustion Chamber

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


Common Traffic Advisory Frequency

The common frequency used by airport traffic to announce position reports in the vicinity of the airport.


Complex Aircraft

An aircraft with retractable landing gear, flaps, and a controllable-pitch propeller, or is turbine powered.


Compression Ratio

1. In a reciprocating engine, the ratio of the volume of an engine cylinder with the piston at the bottom center to the volume with the piston at top center. 2. In a turbine engine, the ratio of the pressure of the air at the discharge to the pressure of air at the inlet.


Compressor Bleed Air

See Bleed Air.


Compressor Bleed Valves

See Bleed Valve.


Compressor Section

The section of a turbine engine that increases the pressure and density of the air flowing through the engine.


Compressor Stall

In gas turbine engines, a condition in an axial-flow compressor in which one or more stages of rotor blades fail to pass air smoothly to the succeeding stages. A stall condition is caused by a pressure ratio that is incompatible with the engine r.p.m. Compressor stall will be indicated by a rise in exhaust temperature or r.p.m. fluctuation, and if allowed to continue, may result in flameout and physical damage to the engine.


Compressor Surge

A severe compressor stall across the entire compressor that can result in severe damage if not quickly corrected. This condition occurs with a complete stoppage of airflow or a reversal of airflow.


Condition Lever

In a turbine engine, a powerplant control that controls the flow of fuel to the engine. The condition lever sets the desired engine r.p.m. within a narrow range between that appropriate for ground and flight operations.


Configuration

This is a general term, which normally refers to the position of the landing gear and flaps.


Constant Speed Propeller

A controllable pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant r.p.m. in spite of varying air loads.


Control Touch

The ability to sense the action of the airplane and its probable actions in the immediate future, with regard to attitude and speed variations, by sensing and evaluation of varying pressures and resistance of the control surfaces transmitted through the cockpit flight controls.


Controllability

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


Controllable Pitch Propeller

A propeller in which the blade angle can be changed during flight by a control in the cockpit.


Conventional Landing Gear

Landing gear employing a third rear-mounted wheel. These airplanes are also sometimes referred to as tailwheel airplanes.


Coordinated Flight

Application of all appropriate flight and power controls to prevent slipping or skidding in any flight condition.


Coordination

The ability to use the hands and feet together subconsciously and in the proper relationship to produce desired results in the airplane.


Core Airflow

Air drawn into the engine for the gas generator.


Cowl Flaps

Devices arranged around certain air-cooled engine cowlings which may be opened or closed to regulate the flow of air around the engine.


Crab

A flight condition in which the nose of the airplane is pointed into the wind a sufficient amount to counteract a crosswind and maintain a desired track over the ground.


Crazing

Small fractures in aircraft windshields and windows caused from being exposed to the ultraviolet rays of the sun and temperature extremes.


Critical Altitude

The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.


Critical Angle Of Attack

The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.


Critical Engine

The engine whose failure has the most adverse effect on directional control.


Cross Controlled

A condition where aileron deflection is in the opposite direction of rudder deflection.


Crossfeed

A system that allows either engine on a twin-engine airplane to draw fuel from any fuel tank.


Crosswind Component

The wind component, measured in knots, at 90° to the longitudinal axis of the runway.


Current Limiter

A device that limits the generator output to a level within that rated by the generator manufacturer.


Cage

The black markings on the ball instrument indicating its neutral position.


Calibrated

The instrument indication compared with a standard value to determine the accuracy of the instrument.


Calibrated orifice

A hole of specific diameter used to delay the pressure change in the case of a vertical speed indicator.


Calibrated airspeed

The speed at which the aircraft is moving through the air, found by correcting IAS for instrument and position errors.


Changeover point (COP)

A point along the route or airway segment between two adjacent navigation facilities or waypoints where changeover in navigation guidance should occur.


Circling approach

A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight- in landing from an instrument approach is not possible or is not desirable.


Class A airspace

Airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 NM of the coast of the 48 contiguous states and Alaska; and designated international airspace beyond 12 NM of the coast of the 48 contiguous states and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied.


Class B airspace

Airspace from the surface to 10,000 feet MSL surrounding the nations busiest airports in terms of IFR operations or passenger numbers. The configuration of each Class B airspace is individually tailored and consists of a surface area and two or more layers, and is designed to contain all published instrument procedures once an aircraft enters the airspace. For all aircraft, an ATC clearance is required to operate in the area, and aircraft so cleared receive separation services within the airspace.


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 is normally 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.


Clean configuration

A configuration in which all flight control surfaces have been placed to create minimum drag. In most aircraft this means flaps and gear retracted.


Clearance

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


Clearance delivery

Control tower position responsible for transmitting departure clearances to IFR flights.


Clearance limit

The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance.


Clearance on request

An IFR clearance not yet received after filing a flight plan.


Clearance void time

Used by ATC, the time at which the departure clearance is automatically canceled if takeoff has not been made. The pilot must obtain a new clearance or cancel the IFR flight plan if not off by the specified time.


Clear ice

Glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets.


Compass course

A true course corrected for variation and deviation errors.


Compass locator

A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS.


Compass rose

A small circle graduated in 360 increments, printed on navigational charts to show the amount of compass variation at different locations, or on instruments to indicate direction.


Computer navigation fix

A point used to define a navigation track for an airborne computer system such as GPS or FMS.


Concentric rings

Dashed-line circles depicted in the plan view of IAP charts, outside of the reference circle, that show en route and feeder facilities.


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 cumuliform 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.


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 brains 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.


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.


Cognitive domain

A grouping of levels of learning associated with mental activity. In order of increasing complexity, the domains are knowledge, comprehension, application, analysis, synthesis, and evaluation.


Compact disk (CD)

A small plastic optical disk which contains recorded music or computer data. Also, a popular format for storing information digitally. The major advantage of a CD is its capability to store enormous amounts of information.


Comprehensiveness

The degree to which a test measures the overall objective.


Computer-assisted instruction

Instruction in which the instructor is responsible for the class and uses the computer to assist in the instruction.


Computer-based training (CBT)

The use of the computer as a training device. CBT is sometimes called computer-based instruction (CBI); the terms and acronyms are synonymous and may be used interchangeably.


Condition

The second part of a performance-based objective which describes the framework under which the skill or behavior will be demonstrated.


Confusion between the symbol and the symbolized object.

Results when a word is confused with what it is meant to represent. Words and symbols create confusion when they mean different things to different people.


Cooperative or group learning

An instructional strategy which organizes students into small groups so that they can work together to maximize their own and each other’s learning.


Correlation

A basic level of learning where the student can associate what has been learned, understood, and applied with previous or subsequent learning.


Course of training

A complete series of studies leading to attainment of a specific goal, such as a certificate of completion, graduation, or an academic degree.


Crew resource management (CRM)

The application of team management concepts in the flight deck environment. It was initially known as cockpit resource management, but as CRM programs evolved to include cabin crews, maintenance personnel and others, the phrase “crew resource management” has been adopted. This includes single pilots, as in most general aviation aircraft. Pilots of small aircraft, as well as crews of larger aircraft, must make effective use of all available resources; human resources, hardware, and information. A current definition includes all groups routinely working with the cockpit crew who are involved in decisions required to operate a flight safely. These groups include, but are not limited to: pilots, dispatchers, cabin crewmembers, maintenance personnel, and air traffic controllers. CRM is one way of addressing the challenge of optimizing the human/machine interface and accompanying interpersonal activities.


Criteria

The third part of a performance-based objective, descriptions of standards that will be used to measure the accomplishment of the objective.


Criterion-referenced testing

System of testing where students are graded against a carefully written, measurable standard or criterion rather than against each other.


Curriculum

A set of courses in an area of specialization offered by an educational institution. A curriculum for a pilot school usually includes courses for the various pilot certificates and ratings.


Cut-away

Model of an object that is built in sections so it can be taken apart to reveal the inner structure.


Calibrated airspeed

The indicated airspeed of an aircraft, corrected for position and instrument error. Calibrated airspeed is equal to true airspeed in standard atmosphere at sea level.


Canard

The forward wing of a canard configuration and may be a fixed, movable, or variable geometry surface, with or without control surfaces.


Canard configuration

A configuration in which the span of the forward wing is substantially less than that of the main wing.


Category

(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means a broad classification of aircraft. Examples include: airplane; rotorcraft; glider; and lighter-than-air; and
(2) As used with respect to the certification of aircraft, means a grouping of aircraft based upon intended use or operating limitations. Examples include: transport, normal, utility, acrobatic, limited, restricted, and provisional.


Category A

With respect to transport category rotorcraft, multiengine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight in the event of engine failure.


Category B

With respect to transport category rotorcraft, single-engine or multiengine rotorcraft which do not fully meet all Category A standards. Category B rotorcraft have no guaranteed stay-up ability in the event of engine failure and unscheduled landing is assumed.


Category II operations

With respect to the operation of aircraft, a straight-in ILS approach to the runway of an airport under a Category II ILS instrument approach procedure issued by the Administrator or other appropriate authority.


Category III operations

With respect to the operation of aircraft, an ILS approach to, and landing on, the runway of an airport using a Category III ILS instrument approach procedure issued by the Administrator or other appropriate authority.


Category IIIa operations

An ILS approach and landing with no decision height (DH), or a DH below 100 feet (30 meters), and controlling runway visual range not less than 700 feet (200 meters).


Category IIIb operations

An ILS approach and landing with no DH, or with a DH below 50 feet (15 meters), and controlling runway visual range less than 700 feet (200 meters), but not less than 150 feet (50 meters).


Category IIIc operations

An ILS approach and landing with no DH and no runway visual range limitation.


Ceiling

The height above the earth’s surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”.


Civil aircraft

Aircraft other than public aircraft.


Class

(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, a classification of aircraft within a category having similar operating characteristics. Examples include: single engine; multiengine; land; water; gyroplane; helicopter; airship; and free balloon; and
(2) As used with respect to the certification of aircraft, a broad grouping of aircraft having similar characteristics of propulsion, flight, or landing. Examples include: airplane; rotorcraft; glider; balloon; landplane; and seaplane.


Clearway

(1) For turbine engine powered airplanes certificated after August 29, 1959, an area beyond the runway, not less than 500 feet wide, centrally located about the extended centerline of the runway, and under the control of the airport authorities. The clearway is expressed in terms of a clearway plane, extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor any terrain protrudes. However, threshold lights may protrude above the plane if their height above the end of the runway is 26 inches or less and if they are located to each side of the runway.
(2) For turbine engine powered airplanes certificated after September 30, 1958, but before August 30, 1959, an area beyond the takeoff runway extending no less than 300 feet on either side of the extended centerline of the runway, at an elevation no higher than the elevation of the end of the runway, clear of all fixed obstacles, and under the control of the airport authorities.


Climbout speed

With respect to rotorcraft, a referenced airspeed which results in a flight path clear of the height-velocity envelope during initial climbout.


Commercial operator

A person who, for compensation or hire, engages in the carriage by aircraft in air commerce of persons or property, other than as an air carrier or foreign air carrier or under the authority of Part 375 of this title. Where it is doubtful that an operation is for “compensation or hire”, the test applied is whether the carriage by air is merely incidental to the person’s other business or is, in itself, a major enterprise for profit.


Configuration, Maintenance, and Procedures (CMP) document

A document approved by the FAA that contains minimum configuration, operating, and maintenance requirements, hardware life-limits, and Master Minimum Equipment List (MMEL) constraints necessary for an airplane-engine combination to meet ETOPS type design approval requirements.


Consensus standard

For the purpose of certificating light-sport aircraft, an industry-developed consensus standard that applies to aircraft design, production, and airworthiness. It includes, but is not limited to, standards for aircraft design and performance, required equipment, manufacturer quality assurance systems, production acceptance test procedures, operating instructions, maintenance and inspection procedures, identification and recording of major repairs and major alterations, and continued airworthiness.


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 covers Class A, Class B, Class C, Class D, and Class E airspace.


Controlled Firing Area

A controlled firing area is established to contain activities, which if not conducted in a controlled environment, would be hazardous to nonparticipating aircraft.


Crewmember

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


Critical altitude

The maximum altitude at which, in standard atmosphere, it is possible to maintain, at a specified rotational speed, a specified power or a specified manifold pressure. Unless otherwise stated, the critical altitude is the maximum altitude at which it is possible to maintain, at the maximum continuous rotational speed, one of the following:
(1) The maximum continuous power, in the case of engines for which this power rating is the same at sea level and at the rated altitude.
(2) The maximum continuous rated manifold pressure, in the case of engines, the maximum continuous power of which is governed by a constant manifold pressure.


Critical engine

The engine whose failure would most adversely affect the performance or handling qualities of an aircraft.


Calendar Month

A time period used by the FAA for certification and currency purposes. A calendar month extends from a given day until midnight of the last day of that month.


Civil Air Regulation (CAR)

Predecessor to the Federal Aviation Regulations.


CAMs

The manuals containing the certification rules under the Civil Air Regulations.


Center of Gravity (CG)

(GAMA) The point at which an airplane would balance if suspended. Its distance from the reference datum is determined by dividing the total moment by the total weight of the airplane. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. It may be expressed in percent of MAC (mean aerodynamic cord) or in inches from the reference Center of Lift. The location along the chord line of an airfoil at which all the lift forces produced by the airfoil are considered to be concentrated.


Centroid

The distance in inches aft of the datum of the center of a compartment or a fuel tank for weight and balance purposes.


CG Arm

(GAMA) The arm obtained by adding the airplane’s individual moments and dividing the sum by the total weight.


CG Limits

(GAMA) The extreme center of gravity locations within which the aircraft must be operated at a given weight. These limits are indicated on pertinent FAA aircraft type certificate data sheets, specifications, or weight and balance records.


CG Limits Envelope

An enclosed area on a graph of the airplane loaded weight and the CG location. If lines drawn from the weight and CG cross within this envelope, the airplane is properly loaded.


CG Moment Envelope

An enclosed area on a graph of the airplane loaded weight and loaded moment. If lines drawn from the weight and loaded moment cross within this envelope, the airplane is properly loaded.


Chord

A straight-line distance across a wing from leading edge to trailing edge.


Curtailment

An operator created and FAA-approved operational loading envelope that is more restrictive than the manufacturer’s CG envelope. It ensures that the aircraft will be operated within limits during all phases of flight. Curtailment typically accounts for, but is not limited to, in-flight movement of passengers and crew, service equipment, cargo variation, seating variation, etc.


Corrected altitude

Indicated altitude of an aircraft altimeter corrected for the temperature of the column of air below the aircraft, the correction being based on the estimated departure of existing temperature from standard atmospheric temperature; an approximation of true altitude.


Calm

The absence of wind or of apparent motion of the air.


Cap cloud

Also called cloud cap. A standing or stationary cap-like cloud crowning a mountain summit.


Ceiling

In meteorology in the U.S., (1) the height above the surface of the base of the lowest layer of clouds or obscuring phenomena aloft that hides more than half of the sky, or (2) the vertical visibility into an obscuration.


Ceiling balloon

A small balloon used to determine the height of a cloud base or the extent of vertical visibility.


Ceiling light

An instrument which projects a vertical light beam onto the base of a cloud or into surface-based obscuring phenomena; used at night in conjunction with a clinometer to determine the height of the cloud base or as an aid in estimating the vertical visibility.


Ceilometer

A cloud-height measuring system. It projects light on the cloud, detects the reflection by a photo-electric cell, and determines height by triangulation.


Celsius temperature scale (abbreviated C)

A temperature scale with zero degrees as the melting point of pure ice and 100 degrees as the boiling point of pure water at standard sea level atmospheric pressure.


Centigrade temperature scale

Same as Celsius temperature scale—a temperature scale with zero degrees as the melting point of pure ice and 100 degrees as the boiling point of pure water at standard sea level atmospheric pressure.


Chaff

Pertaining to radar, (1) short, fine strips of metallic foil dropped from aircraft, usually by military forces, specifically for the purpose of jamming radar; (2) applied loosely to echoes resulting from chaff.


Change of state

In meteorology, the transformation of water from one form, i.e., solid (ice), liquid, or gaseous (water vapor), to any other form. There are six possible transformations designated by the five terms following: condensation, evaporation, freezing, melting, or sublimation.


Condensation

The change of water vapor to liquid water.


Chinook

A warm, dry foehn wind blowing down the eastern slopes of the Rocky Mountains over the adjacent plains in the U.S. and Canada.


Cirriform

All species and varieties of cirrus, cirrocumulus, and cirrostratus clouds; descriptive of clouds composed mostly or entirely of small ice crystals, usually transparent and white; often producing halo phenomena not observed with other cloud forms. Average height ranges upward from 20,000 feet in middle latitudes.


Cirrocumulus

A cirriform cloud appearing as a thin sheet of small white puffs resembling flakes or patches of cotton without shadows; sometimes confused with altocumulus.


Cirrostratus

A cirriform cloud appearing as a whitish veil, usually fibrous, sometimes smooth; often produces halo phenomena; may totally cover the sky.


Cirrus

A cirriform cloud in the form of thin, white feather-like clouds in patches or narrow bands; have a fibrous and/or silky sheen; large ice crystals often trail downward a considerable vertical distance in fibrous, slanted, or irregularly curved wisps called mares’ tails.


Clear air turbulence

Turbulence encountered in air where no clouds are present; more popularly applied to high level turbulence associated with wind shear. (abbreviated CAT)


Clear icing (or clear ice)

Generally, the formation of a layer or mass of ice which is relatively transparent because of its homogeneous structure and small number and size of air spaces; used commonly as synonymous with glaze, particularly with respect to aircraft icing. Compare with rime icing. Factors which favor clear icing are large drop size, such as those found in cumuliform clouds, rapid accretion of supercooled water, and slow dissipation of latent heat of fusion.


Climate

The statistical collective of the weather conditions of a point or area during a specified interval of time (usually several decades); may be expressed in a variety of ways.


Climatology

The study of climate.


Clinometer

An instrument used in weather observing for measuring angles of inclination; it is used in conjunction with a ceiling light to determine cloud height at night.


Cloud bank

Generally, a fairly well-defined mass of cloud observed at a distance; it covers an appreciable portion of the horizon sky, but does not extend overhead.


Cloudburst

In popular terminology, any sudden and heavy fall of rain, almost always of the shower type.


Cloud cap

Also called a cap cloud. A standing or stationary cap-like cloud crowning a mountain summit.


Cloud detection radar

A vertically directed radar to detect cloud bases and tops.


Cold front

Any non-occluded front which moves in such a way that colder air replaces warmer air.


Condensation level

The height at which a rising parcel or layer of air would become saturated if lifted adiabatically.


Condensation nuclei

Small particles in the air on which water vapor condenses or sublimates.


Condensation trail (or contrail) (also called vapor trail)

A cloud-like streamer frequently observed to form behind aircraft flying in clear, cold, humid air.


Conditionally unstable air

Unsaturated air that will become unstable on the condition it becomes saturated.


Conduction

The transfer of heat by molecular action through a substance or from one substance in contact with another; transfer is always from warmer to colder temperature.


Constant pressure chart

A chart of a constant pressure surface; may contain analyses of height, wind, temperature, humidity, and/or other elements.


Continental polar air

Also called polar air. An air mass with characteristics developed over high latitudes, especially within the subpolar highs. Continental polar air (cP) has cold surface temperatures, low moisture content, and, especially in its source regions, has great stability in the lower layers. It is shallow in comparison with Arctic air.


Continental tropical air

Also called tropical air. An air mass with characteristics developed over low latitudes. Continental tropical (cT) is produced over subtropical arid regions and is hot and very dry.


Contour

In meteorology, (1) a line of equal height on a constant pressure chart; analogous to contours on a relief map; (2) in radar meteorology, a line on a radar scope of equal echo intensity.


Contouring circuit

On weather radar, a circuit which displays multiple contours of echo intensity simultaneously on the plan position indicator or range-height indicator scope. A line on a radar scope of equal echo intensity.


Contrail

Contraction for condensation trail.


Convection

(l) In general, mass motions within a fluid resulting in transport and mixing of the properties of that fluid. (2) In meteorology, atmospheric motions that are predominantly vertical, resulting in vertical transport and mixing of atmospheric properties; distinguished from advection.


Convective cloud

Cumuliform. A term descriptive of all convective clouds exhibiting vertical development in contrast to the horizontally extended stratiform types.


Convective condensation level (abbreviated CCL)

The lowest level at which condensation will occur as a result of convection due to surface heating. When condensation occurs at this level, the layer between the surface and the CCL will be thoroughly mixed, temperature lapse rate will be dry adiabatic, and mixing ratio will be constant.


Convective instability

The state of an unsaturated layer of air whose lapse rates of temperature and moisture are such that when lifted adiabatically until the layer becomes saturated, convection is spontaneous.


Convergence

The condition that exists when the distribution of winds within a given area is such that there is a net horizontal inflow of air into the area. In convergence at lower levels, the removal of the resulting excess is accomplished by an upward movement of air; consequently, areas of low-level convergent winds are regions favorable to the occurrence of clouds and precipitation. Compare with divergence.


Coriolis force

A deflective force resulting from earth’s rotation; it acts to the right of wind direction in the Northern Hemisphere and to the left in the Southern Hemisphere.


Corona

A prismatically colored circle or arcs of a circle with the sun or moon at its center; coloration is from blue inside to red outside (opposite that of a halo); varies in size (much smaller) as opposed to the fixed diameter of the halo; characteristic of clouds composed of water droplets and valuable in differentiating between middle and cirriform clouds.


Corposant

St. Elmo’s Fire. A luminous brush discharge of electricity from protruding objects, such as masts and yardarms of ships, aircraft, lightning rods, steeples, etc., occurring in stormy weather. Also called corposant.


Cumuliform

A term descriptive of all convective clouds exhibiting vertical development in contrast to the horizontally extended stratiform types.


Cumulonimbus

A cumuliform cloud·type; it is heavy and dense, with considerable vertical extent in the form of massive towers; often with tops in the shape of an anvil or massive plume; under the base of cumulonimbus, which often is very dark, there frequently exists virga, precipitation and low ragged clouds (scud), either merged with it or not; frequently accompanied by lightning, thunder, and sometimes hail; occasionally produces a tornado or a waterspout; the ultimate manifestation of the growth of a cumulus cloud, occasionally extending well into the stratosphere.


Cumulonimbus mamma

A cumulonimbus cloud having hanging protuberances, like pouches, festoons, or udders, on the under side of the cloud; usually indicative of severe turbulence.


Cumulus

A cloud in the form of individual detached domes or towers which are usually dense and well defined; develops vertically in the form of rising mounds of which the bulging upper part often resembles a cauliflower; the sunlit parts of these clouds are mostly brilliant white; their bases are relatively dark and nearly horizontal.


Cumulus fractus

Cumulus clouds ( Clouds in the form of individual detached domes or towers which are usually dense and well defined) in the form of irregular shreds, appearing as if torn; have a clearly ragged appearance; applies only to stratus and cumulus, i.e., cumulus fractus and stratus fractus.


Cyclogenesis

Any development or strengthening of cyclonic circulation in the atmosphere.


Cyclone

(l) An area of low atmospheric pressure,. which has a closed circulation that is cyclonic, i.e., as viewed from above, the circulation is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere, undefined at the Equator. Because cyclonic circulation and relatively low atmospheric pressure usually co-exist, in common practice the terms cyclone and low are used interchangeably. Also, because cyclones often are accompanied by inclement (sometimes destructive) weather, they are frequently referred to simply as storms. (2) Frequently misused to denote a tornado. (3) In the Indian Ocean, a tropical cyclone of hurricane or typhoon force.


Civil twilight

The period of time before sunrise and after sunset when the sun is not more than 6° below the horizon.


Cabin altitude

Cabin pressure in terms of equivalent altitude above sea level.


Cage

The black markings on the ball instrument indicating its neutral position.


Calibrated

The instrument indication compared with a standard value to determine the accuracy of the instrument.


Calibrated orifice

A hole of specific diameter used to delay the pressure change in the case of a vertical speed indicator.


Calibrated airspeed

The speed at which the aircraft is moving through the air, found by correcting IAS for instrument and position errors.


Camber

The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.


Canard

A horizontal surface mounted ahead of the main wing to provide longitudinal stability and control. It may be a fixed, movable, or variable geometry surface, with or without control surfaces.


Canard configuration

A configuration in which the span of the forward wings is substantially less than that of the main wing.


Cantilever

A wing designed to carry loads without external struts.


Ceiling

The height above the earth’s surface of the lowest layer of clouds, which is reported as broken or overcast, or the vertical visibility into an obscuration.


Center of gravity (CG)

The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percentage of mean aerodynamic chord (MAC). The location depends on the distribution of weight in the airplane.


Center of gravity limits

The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.


Center of gravity range

The distance between the forward and aft CG limits indicated on pertinent airplane specifications.


Center of pressure

A point along the wing chord line where lift is considered to be concentrated. For this reason, the center of pressure is commonly referred to as the center of lift.


Centrifugal flow compressor

An impeller-shaped device that receives air at its center and slings the air outward at high velocity into a diffuser for increased pressure. Also referred to as a radial outflow compressor.


Centrifugal force

An outward force, that opposes centripetal force, resulting from the effect of inertia during a turn.


Centripetal force

A center-seeking force directed inward toward the center of rotation created by the horizontal component of lift in turning flight.


Changeover point (COP)

A point along the route or airway segment between two adjacent navigation facilities or waypoints where changeover in navigation guidance should occur.


Checklist

A tool that is used as a human factors aid in aviation safety. It is a systematic and sequential list of all operations that must be performed to properly accomplish a task.


Chord line

An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.


Circling approach

A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight-in landing from an instrument approach is not possible or is not desirable.


Class A airspace

Airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 NM of the coast of the 48 contiguous states and Alaska; and designated international airspace beyond 12 NM of the coast of the 48 contiguous states and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied.


Class B airspace

Airspace from the surface to 10,000 feet MSL surrounding the nation’s busiest airports in terms of IFR operations or passenger numbers. The configuration of each Class B airspace is individually tailored and consists of a surface area and two or more layers, and is designed to contain all published instrument procedures once an aircraft enters the airspace. For all aircraft, an ATC clearance is required to operate in the area, and aircraft so cleared receive separation services within the airspace.


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 is normally 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.


Clean configuration

A configuration in which all flight control surfaces have been placed to create minimum drag. In most aircraft this means flaps and gear retracted.


Clearance

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


Clearance delivery

Control tower position responsible for transmitting departure clearances to IFR flights.


Clearance limit

The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance.


Clearance on request

An IFR clearance not yet received after filing a flight plan.


Clearance void time

Used by ATC, the time at which the departure clearance is automatically canceled if takeoff has not been made. The pilot must obtain a new clearance or cancel the IFR flight plan if not off by the specified time.


Clear ice

Glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets.


Coefficient of lift

The ratio between lift pressure and dynamic pressure.


Cold front

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


Compass course

A true course corrected for variation and deviation errors.


Compass locator

A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS.


Compass rose

A small circle graduated in 360° increments, to show direction expressed in degrees.


Complex aircraft

An aircraft with retractable landing gear, flaps, and a controllable pitch propeller.


Compressor pressure ratio

The ratio of compressor discharge pressure to compressor inlet pressure.


Compressor stall

In gas turbine engines, a condition in an axial-flow compressor in which one or more stages of rotor blades fail to pass air smoothly to the succeeding stages. A stall condition is caused by a pressure ratio that is incompatible with the engine rpm. Compressor stall will be indicated by a rise in exhaust temperature or rpm fluctuation, and if allowed to continue, may result in flameout and physical damage to the engine.


Computer navigation fix

A point used to define a navigation track for an airborne computer system such as GPS or FMS.


Concentric rings

Dashed-line circles depicted in the plan view of IAP charts, outside of the reference circle, that show en route and feeder facilities.


Condensation

A change of state of water from a gas (water vapor) to a liquid.


Condensation nuclei

Small particles of solid matter in the air on which water vapor condenses.


Cone of confusion

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


Configuration

This is a general term, which normally refers to the position of the landing gear and flaps.


Constant-speed propeller

A controllable-pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant rpm in spite of varying air loads.


Continuous flow oxygen system

System that supplies a constant supply of pure oxygen to a rebreather bag that dilutes the pure oxygen with exhaled gases and thus supplies a healthy mix of oxygen and ambient air to the mask. Primarily used in passenger cabins of commercial airliners.


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.


Controllability

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


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 cumuliform clouds.


Convective SIGMET

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


Conventional landing gear

Landing gear employing a third rear-mounted wheel. These airplanes are also sometimes referred to as tailwheel airplanes.


Coordinated flight

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


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 to stimulate the brain’s motion sensing system.


Coupled ailerons and rudder

Rudder and ailerons are connected with interconnected springs in order to counteract adverse yaw. Can be overridden if it becomes necessary to slip the aircraft.


Course

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


Cowl flaps

Shutter-like devices arranged around certain air-cooled engine cowlings, which may be opened or closed to regulate the flow of air around the engine.


Crew resource management (CRM)

The application of team management concepts in the flight deck environment. It was initially known as cockpit resource management, but as CRM programs evolved to include cabin crews, maintenance personnel, and others, the phrase “crew resource management” was adopted. This includes single pilots, as in most general aviation aircraft. Pilots of small aircraft, as well as crews of larger aircraft, must make effective use of all available resources; human resources, hardware, and information. A current definition includes all groups routinely working with the flight crew who are involved in decisions required to operate a flight safely. These groups include, but are not limited to pilots, dispatchers, cabin crewmembers, maintenance personnel, and air traffic controllers. CRM is one way of addressing the challenge of optimizing the human/machine interface and accompanying interpersonal activities.


Critical altitude

The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.


Critical angle of attack

The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.


Critical areas

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


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.


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