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Administrator or other appropriate authority.”
Category III operations. 14 CFR Part 1: “With respect to the operation of aircraft, means an ILS
approach to and landing on, the runway of an airport using a Category III ILS approach procedure issued
by the Administrator or other appropriate authority.”
catenary curve. A curve formed by a flexible cable suspended between two points at the same level.
cathedral (aerodynamics). Negative dihedral. The wings of an airplane, as they are viewed from the front,
are not usually straight; they normally angle upward from the center. This upward angling is called positive
dihedral, and it improves the stability of the airplane.
However, when maneuverability is more important than stability, as it is on some military fighters
and acrobatic airplanes, the wings are set with negative dihedral (cathedral). The wings angle downward
from the center.
Cathedral decreases the stability of an airplane and makes it more maneuverable.
cathode of an electrochemical cell. The active element in an electrochemical cell that is reduced, or loses
oxygen in the chemical action which causes electrons to flow.
cathode of a semiconductor diode. The end of a semiconductor diode made of N-type material. When the
diode is forward biased with the negative terminal of the power source connected to the cathode of the
diode, electrons flow through the diode. The cathode of a semiconductor diode is identified by the bar in
the diode symbol.
cathode rays. Streams of electrons emitted by the cathode in a special form of electron tube called a
cathode-ray tube (CRT). These electrons are accelerated by the attraction of a positive voltage on special
grids called accelerator grids. The cathode rays strike a phosphorescent material that covers the inside of
the face of the tube, and when they strike it, the material glows.
Cathode-ray tubes are used as the display in computers and oscilloscopes.
cathode-ray tube. See CRT.
cathodic area. An area within a piece of metal to which electrons from the anodic area have migrated.
cathodic protection. Another name for sacrificial corrosion. A material that is more anodic than the
material being protected is attached to or plated on the material. This becomes the anode and is corroded,
while the part being protected is the cathode and it is not damaged.
cation. A positive ion that moves toward the cathode in the process of electrolysis.
catwalk. A narrow walkway inside a structure that allows a person to move through an area that is
otherwise inaccessible.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 111
caustic material. Any material that can eat away another material by chemical action. Both strong acids
and strong aklalis are caustic materials.
caustic soda. A common name for sodium hydroxide, NaOH. Caustic soda is often called lye.
cavitation. A condition that exists in a fluid pump when there is not enough pressure in the reservoir to
force fluid to the inlet of the pump. The pump picks up air instead of fluid.
cavity. An empty (unfilled) space. A cavity is the same as a hole.
C-battery (radio battery). A small, low-voltage battery used in some of the older, battery-powered,
tube-type radios to provide a grid bias voltage for some of the vacuum tubes.
C-batteries have generally been replaced by a method of biasing the tubes with the voltage drop
across a resistor.
C-check. See maintenance checks.
CCL (convective condensation level). 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, the temperature lapse rate will be dry adiabatic (3°C per 1,000 feet), and the mixing
ratio will be constant.
C-clamp. A screw-type clamp made in the shape of the letter C. One jaw is fixed, and the other is mounted
on a screw.
CD duct. See convergent-divergent duct.
CDI (course deviation indicator). An indicator used with VOR, LORAN, or GPS navigation systems to
indicate the direction and relative amount of deviation from the desired course. CDIs are often called
Left-Right indicators.
CDU (control display unit). A component in a flight management computer system that contains a
cathode-ray tube and a keyboard with alphanumeric keys and mode-select and line-select keys. The CDU
allows the flight crew to access the data to be displayed.
Ceconite. The registered trade name for an inorganic aircraft fabric woven of polyester fibers. Ceconite is
installed on the structure and then shrunk with heat.
ceiling (meteorological condition). 14 CFR Part 1: “The height above the earth’s surface of the lowest
　
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