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Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 128
Class B airspace. Generally, that airspace from the surface to 10,000 feet MSL surrounding the nation’s
busiest airports in terms of IFR operations or passenger emplanements. The configuration of each Class B
airspace is individually tailored and consists of a surface area and two or more layers (some Class B
airspace areas resemble upside down wedding cakes), and is designed to contain all published instrument
procedures once an aircraft enters the airspace. An ATC clearance is required for all aircraft to operate in
the area, and all aircraft so cleared receive separation services within the airspace. The cloud clearance
requirement for VFR operations is “clear of clouds.”
class-B amplifier (electronic amplifier). An electronic amplifier whose output current flows only during
one half of the input cycle. Two class-B amplifiers can be connected in such a way that each amplifies one
half of the input signal. Both amplifiers are connected to a single output device. Class-B amplifiers are
called push-pull amplifiers.
Class B fire. A fire that has combustible liquids as its fuel.
Class C airspace. Generally, that airspace from the surface to 4,000 feet above the airport elevation
(charted in MSL) surrounding those airports that have an operational control tower, are serviced by radar
approach control, and that have a certain number of IFR operations or passenger emplanements. 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-C amplifier (electronic amplifier). An electronic amplifier whose output current flows only during a
small portion of one half of the input cycle. Class-C amplifiers are used to sustain radio-frequency
oscillators by supplying pulses of energy to replace the energy lost in the resistance in the circuit.
Class C fire. A fire which involves energized electrical equipment.
Class D airspace. Generally, that 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 will normally be designed to contain the procedures.
Class D fire. A fire in which a metal such as magnesium burns.
Class E airspace. Generally, if the airspace is not Class A, Class B, Class C, or Class D, and it is
controlled airspace, it is Class E airspace.
Class G airspace. Generally that airspace that is uncontrolled, and has not been designated as Class A,
Class B, Class C, Class D, or Class E airspace.
class of thread (threaded fastener condition). A method of classifying the fit of threads used in bolts and
nuts. A class-1 fit is a loose fit, a class-2 fit is a free fit, a class-3 fit is a medium fit, a class-4 fit is a close
fit, and a class-5 fit is a wrench fit. Most fasteners used in aircraft structure have a class-3 fit.
claw hammer. A hammer used for driving and removing nails from wood. The claws which are used to
remove nails may be either straight or curved.
clean room. A special room used for manufacturing and servicing precision equipment. The air in a clean
room is filtered, and special precautions are taken to prevent dust, dirt, or other contamination entering the
room. The workers wear special clothing to prevent contamination from their street clothes or from their
hair.
clear air turbulence. See CAT.
clearance (physical clearance). The distance or space between moving parts that allows free movement.
clearance limit (air traffic control). The fix, point, or location to which an aircraft is cleared when issued
an air traffic clearance.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 129
“Clearance void if not off by (time)” (air traffic control). A phrase used by ATC to advise an aircraft
that the departure clearance is automatically canceled if takeoff is not made prior to a specific time.
The pilot must obtain a new clearance or cancel his IFR flight plan if not off by the specified time.
clearance volume (reciprocating engine measurement). The volume of the cylinder of a reciprocating
engine when the piston is at the top of its stroke.
“Cleared as filed” (air traffic control). A statement meaning the aircraft is cleared to proceed in
accordance with the route of flight filed in the flight plan.
　
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