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idiot light. A warning light, whose proper name is nondiscrete indicator, used instead of an indicating
instrument. Some aircraft have “idiot lights” rather than ammeters, to alert the pilot when the generator is
not producing adequate voltage. Other idiot lights indicate such conditions as low oil pressure and cabin
heater malfunctions.
idle cut-off (reciprocating engine fuel metering system). The position of the mixture control in a
reciprocating engine fuel metering system that shuts off all fuel to the cylinders. Most aircraft engine fuel
metering systems have a mixture control that allows the pilot to adjust the fuel-air mixture ratio to
compensate for changes in air density as the aircraft goes up in altitude. When this mixture control is placed
in the idle cut-off position, all fuel is shut off to the cylinders and the engine stops running.
idle mixture (reciprocating engine fuel metering system). The fuel-air mixture ratio used by an aircraft
engine while it is operating at its idle speed. The uneven distribution of the fuel-air mixture to the cylinders
at idle speed requires the idle mixture ratio to be richer than that required for best burning.
idler gear (gear train). A gear used to reverse the direction of rotation of another gear without changing its
speed of rotation. An idler gear does not add nor take away mechanical advantage from the gear train.
idler pulley (belt-drive system). A pulley in a belt-drive system used to adjust the tension on the belt that
joins a drive pulley with a driven pulley. The idler pulley does not change the direction of rotation of either
pulley, nor does it change the speed relationship between the pulleys.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 312
idle speed. The lowest speed at which an engine operates smoothly when it is not carrying any type of
mechanical load. Idle speed is measured in revolutions per minute (RPM).
idle thrust (gas turbine engine). The thrust produced by an aircraft gas turbine engine when the power
control lever is pulled back to the idle stop. 14 CFR Part 1: “The jet thrust obtained with the engine power
control lever set at the stop for the least thrust position at which it can be placed.”
idling current (electronic equipment). Current flowing in an electronic circuit when there is no input
signal requiring the system to act. Idling current, also called quiescent current, is normally much less than
the operating current of the system.
IFF (identification, friend or foe). An electronic identification system that is the forerunner of the modern
radar beacon transponder used by air traffic controllers to identify specific aircraft. IFF, developed in the
latter part of World War II, is an electronic pulse system in which interrogation pulses of electrical energy
are transmitted from a ground station and received in the aircraft.
If the airborne equipment is set to respond with the proper code, the IFF identifies the aircraft as
friendly. But if the equipment does not reply with the correct code, the ground station is alerted to the fact
that the indications received on its radarscope may be caused by a foe, or enemy. The principles of IFF
equipment apply to other pulse navigation systems, especially aircraft radar beacon transponders and
distance measuring equipment (DME).
IFIM (International Flight Information Manual). A publication designed primarily as a pilot’s preflight
planning guide for flights into foreign airspace and for flights returning to the U.S. from foreign locations.
“If no transmission received for [time]” (air traffic control). A phrase used by ATC in radar approaches
to prefix procedures which should be followed by the pilot in event of lost communications.
IFR (instrument flight rules). Rules and regulations established by the Federal Aviation Administration to
govern flight under conditions in which flight by outside visual reference is not safe. Instrument flight rules
govern the flight of aircraft along the federally controlled airways and airports, and this flight is directed
and controlled by operators on the ground. Flight according to instrument flight rules depends upon flying
by reference to instruments in the cockpit, and navigation is done by reference to electronic signals.
IFR aircraft (air traffic control). An aircraft conducting flight in accordance with instrument flight rules.
IFR conditions. 14 CFR Part 1: “Weather conditions below the minimums allowed for flight under visual
flight rules.”
IFR military training routes (air traffic control). Routes used by the Department of Defense and
associated Reserve and Air Guard units for the purpose of conducting low-altitude navigation and tactical
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航空术语词典Dictionary of Aeronautical Terms 中(79)
