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incursion. Entry into something. Runway incursion occurs when an aircraft taxies onto a runway.
indefinite ceiling (meteorology). A ceiling classification denoting vertical visibility into a surface-based
obscuration.
indicated altitude. The altitude above mean sea level shown on a pressure altimeter when the local
altimeter setting is adjusted into the barometric scale. The altimeter setting is the barometric pressure
existing at the reporting station, corrected to the value it would have if the station were located at sea level.
Indicated altitude is used by all aircraft flying below 18,000 feet. At higher altitudes, aircraft use
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pressure altitude, in which the barometric scale is adjusted to standard sea-level barometric pressure of
29.92 inches of mercury, or 1013.2 millibars.
indicated airspeed. 14 CFR Part 1: “The speed of an aircraft as shown on its pitot static airspeed indicator,
calibrated to reflect standard atmospheric adiabatic compressible flow at sea level uncorrected for airspeed
system errors.”
indicating fuse holder. A type of electrical fuse holder that shows when a fuse has blown and opened the
circuit. A small neon bulb is installed in the fuse holder, in parallel with the fuse. The resistance of a good
fuse is so low that when current flows through it, there is not enough voltage drop across it to illuminate the
bulb.
But if the fuse blows and opens the circuit, the entire system voltage is dropped across the neon
bulb, and it illuminates. The bulb does not allow enough current to flow to damage the circuit.
indicating instrument. An instrument that shows in a visual form the value it is sensing. There are two
basic types of indicating instruments: instruments that give their indication in an analog form, and
instruments that have a digital readout.
An analog instrument has a dial and one or more pointers. The position of the pointer on the dial is
an analog, or representation, of the value the indicator is sensing. A digital instrument uses numbers to
indicate the value it is sensing. An ordinary clock is a form of analog indicating instrument. The number of
degrees the hands have moved past their straight-up position relates to the number of hours, minutes, or
seconds that have passed since noon or midnight. A digital clock uses just numbers to indicate the seconds,
minutes, and hours that have passed since noon or midnight.
indirect light. Light that falls on an object after it has been reflected from a nonlight-producing object.
indirectly heated cathode (vacuum tube component). A cathode in a vacuum tube that is heated by a
filament which is not a part of the cathode. The cathode is made in the form of a metal tube whose surface
is coated with a material that emits electrons when it is heated. The filament, a small resistance-wire heater
inside the cathode, heats it but does not touch it. Indirectly heated cathodes allow the filament to be heated
with alternating current without causing the hum that would be present if the AC passed through the
cathode itself.
indium. A soft, malleable, silvery-white, metallic chemical element. Indium’s symbol is In, its atomic
number is 49, and its atomic weight is 114.82. Indium is used as a plating over silver in making mirrors and
as a component in semiconductors.
induced current. Electrical current produced in a conductor when it is cut, or crossed, by changing lines of
magnetic flux. Induced current always flows in the opposite direction to the current that produced the
magnetic flux.
induced drag (aerodynamics). Aerodynamic drag produced by an airfoil when it is producing lift. The
amount of induced drag is determined by the shape and the area of the airfoil, the angle of attack, the air
density, and the speed of the air moving over the airfoil.
induced voltage. Voltage generated in a conductor when it is cut, or crossed, by lines of magnetic flux.
There are three ways a conductor can be cut by lines of magnetic flux: (1) The conductor can be held
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stationary and the magnetic field moved back and forth across it. (2) The conductor can be moved back and
forth through a stationary magnetic field. (3) Both the conductor and the magnetic field can be held
stationary, but the magnetic field can be produced by alternating current, which constantly changes its
direction and strength.
inducer (turbine engine component). Rotating inlet guide vanes installed on the center of a centrifugal
compressor to pick up the inlet air and direct it at the correct angle into the impeller blades.
inductance. The electrical characteristic of a conductor which causes a voltage to be produced when it is
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航空术语词典Dictionary of Aeronautical Terms 中(84)
