C of A - Certificate of Airworthiness issued by the CAA indicating that an aircraft meets the Authority's airworthiness standards. Cs of A are issued to individual aircraft, and also to generic aircraft types (Type Certification in the USA) when the first example of a type is registered. Cs of A on individual aircraft are granted in several categories, e.g. Private, Public Transport, Aerial Work etc. and much be renewed at intervals. Permits to Fly are authorisations granted to aircraft such as homebuilts, vintage aeroplanes, warbirds and some simple classic light aircraft which are not required to meet the standards demanded for a full C of A, and are accordingly restricted in the kinds of operation for which they may be used.
C of E - Certificate of Experience, valid for private pilot licence holders for thirteen months, and renewed by flight test or evidence of completing the minimum required flying experience in the preceding thirteen month period. Also C of T, certificate of test. C of G - centre of gravity. The point on an aircraft through which the entire aircraft's weight may be assumed to act (i.e. around which the aircraft, if suspended, would balance). C of G limits are the most forward and rearward positions of the C of G permitted for safe operation. An aircraft loaded outside its C of G limits can be difficult or impossible to control.
C of P - centre of pressure, the point through which the total effect of lift may be said to act on an aeroplane.
C/L - centre line (of a runway, for example).
c/s - call sign.
CAA - Civil Aviation Authority. CAAFU - Civil Aviation Authority Flying Unit, based at Stansted Airport, which performs such tasks as navaid checking and calibration and also examines candidates for instrument ratings and commercial pilot's licences.
CAD/CAM - computer aided design/manufacture. CANP - Civil Aviation Notification Procedure. A voluntary system whereby civil operators notify their intention to fly at low level (at or below 1,000 feet agl, when crop spraying or powerline inspecting for example), aimed at avoiding conflict with low flying military aircraft.
CAP - Civil Air Publication. Information booklets issued by the CAA, e.g. CAP 53 The Private Pilot Licence.
CAS - calibrated airspeed indicated airspeed corrected for air density and compressibility.
casevac - casualty evacuation.
CAT - clear air turbulence. Also CATegory when referring to certain instrument landing systems which require special aircraft instrumentation, certification and pilot qualification beyond those needed for standard instrument approaches (e.g. a CAT IIIC ILS permits operation down to the surface of the runway without external visual reference, true zero zero operation). CAVOK - pronounced CAV okay (ceiling and visibility OK), visibility at least ten kilometres, with no cloud below 5,000 feet, with no Cbs, precipitation, thunderstorms, shallow fog or low drifting snow.
CAVU - ceiling and visibility unlimited. Cloudless (or scattered cloud) conditions with visibility in excess of ten kilometres.
CDI - course deviation indicator. The vertical needle of a VOR indicator which shows the aircraft's position relative to the selected VOR radial.
CDU - control display unit.
ceiling - height above ground or water of the base of the lowest layer of cloud below 20,000 feet which covers more than half of the sky. An aircraft's service ceiling is the density altitude (which see) at which its maximum rate of climb is no greater than 100 feet per minute. Its absolute ceiling is the highest altitude at which it can maintain level flight.
CFI - chief flying instructor (certified flying instructor in USA).
CH - compass heading. Check 'A' - a thorough pre flight inspection the first of the day.
CHIRP - Confidential Human Factors Incident Reporting system, whereby professional pilots and ATC staff may report in confidence incidents arising from human errors for analysis by the RAF Institute of Aviation Medicine at Farnborough.
CHT - cylinder head temperature (gauge). A device which, by means of a probe(s) gives a cockpit readout of the temperature of one or more of an aircraft engine's cylinder heads. circuit - pattern around which aircraft fly when arriving at an airfield, usually rectangular in UK but not necessarily elsewhere. The circuit (pattern in USA) is aligned with the active runway and may be either left or right handed. Dead side is the opposite side of the circuit pattern in operation from which arriving aircraft join for landing. See also final(s).
clean - flaps, slats and undercarriage retracted and on military aircraft no external missliles etc.
clearance - authorization from air traffic control to proceed as requested or instructed. Used for ground and air manoeuvring, thus "cleared for take off", "cleared flight planned route", "cleared to descend" etc.
Clouds - commonly used abbreviations for cloud types:
AC = altocumulus
AS = altostratus
CB = cumulonimbus
CC = cirrocumulus
CI = cirrus
CS = cirrostratus
CU = cumulus
NS = nimbo stratus
SC = stratocumulus
ST = stratus
Com(m)(s) - communication(s)
CPL - Commercial Pilot's Licence
CR or C/R - counter rotating. Usually in general aviation referring to twin engined aircraft with 'handed' engines whose propellers turn in opposite directions to eliminate propeller torque effect.
critical altitude - the highest density altitude at which it is possible to maintain the maximum continuous rated power or manifold pressure of an aero engine.
critical engine - the engine on a mult-engined aircraft whose failure would most seriously effect performance or handling of the aircraft, through asymmetric effects or loss of power to systems such as hydraulics.
CRP - compulsory reporting point.
CRS course - the intended direction of flight in the horizontal plane expressed in degrees of the compass.
CRT - cathode ray tube (like a television). Used in flight deck displays of new EFIS, below. jets instead of conventional instruments. See also generation airliners, business aircraft and military
CS - constant-speed (propeller). A variable pitch propeller which maintains constant rpm by automatically changing blade angle. Also CSU, constant speed unit.
CTA - Control Area. An area of controlled airspace extending upwards from specified limit agl.
CTR - Control Zone. An area of controlled airspace extending upwards from ground level to a specified upper limit.
CVR - cockpit voice recorder. A tape recorder installed on the flight decks of commercial transport aircraft and helicopters and some business aeroplanes to record crew conversation, RT transmissions and cockpit background noises (e.g. trim wheel operation, flap motor running) in case required for incident or accident investigation.