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established airway/route. Normally associated with area navigation (RNAV) operations.
parallel operation (computer operation). Data transfer by moving digital words (groups of bits) all at one
time. Parallel operation is much faster than serial operation, in which the bits are moved one at a time, but it
requires much more complex circuitry.
parallel resonant circuit (electronic circuit). A circuit consisting of an inductor and capacitor connected
in parallel. The impedance, or the total opposition to the flow of current, of a parallel resonant circuit is
maximum at the frequency to which the circuit is resonant. A parallel resonant circuit is called a tank
circuit.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 427
parallel runways. Two or more runways at the same airport whose center lines are parallel. In addition to
runway number, parallel runways are designated as L (left) and R (right) or, if three parallel runways exist,
L (left), C (center), and R (right).
parallels of latitude. Imaginary lines on the surface of the earth parallel to the equator. Parallels of latitude
are used as north and south reference lines for map making and navigation. The equator is the 0° parallel of
latitude, the geographic north pole is located at 90° north latitude, and the geographic south pole is located
at 90° south latitude.
parallel-wound motor. A DC electric motor whose field coils are connected in parallel with the armature.
A parallel-wound motor has a low starting torque, but it operates at a relatively constant speed.
paramagnetic material. A material whose permeability is greater than that of a vacuum (permeability of
one) but less than that of a ferromagnetic material. The permeability of a paramagnetic material does not
change as the magnetizing force applied to it changes. Some alloys of nickel and titanium are
paramagnetic.
parameter. A quantity whose value determines characteristics or behavior. Temperature, pressure, and
humidity are parameters of the atmosphere.
parasite drag (aerodynamic drag). A form of aerodynamic drag caused by friction between the air and
the surface over which it is flowing. Parasite drag increases as the velocity of the air increases.
parasol wing airplane. An airplane with a single main wing mounted on struts above the fuselage. The
struts between the wing and the fuselage are called cabane struts.
parcel (meteorology). A volume of air small enough to contain uniform distribution of its meteorological
properties, and large enough to remain relatively self-contained and respond to all meteorological processes.
No specific dimensions have been defined for a parcel; however, the order of magnitude of one cubic foot
has been suggested.
parent metal (welding). The metal being welded. This term is used to distinguish it from the metal of the
welding rod.
Parkerizing (corrosion protection). The registered trade name for a process in which a steel part is
covered with a hard oxide film that prevents oxygen reaching the metal. The oxide film is formed by
soaking the steel in a solution of phosphoric acid and manganese or zinc dioxide.
Parker-Kalon screw. The registered trade name for a self-tapping sheet metal screw, often called a PK
screw. Parker-Kalon screws, made of hardened steel and having sharp, coarse threads, are used to hold thin
sheets of metal together. As the screw is turned through matching holes in the thin metal, the threads clamp
the sheets tightly together. See illustration for panhead screw.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 428
parking brake. A brake system used to keep an aircraft from rolling when it is parked. The parking brake
holds pressure on the brake system when there is no operator at the controls.
partial obscuration (meteorology). A designation of sky cover when part of the sky is hidden by
surface-based obscuring phenomena.
partial-panel instrument flight. Instrument flight by reference to only a limited number of flight
instruments. Partial-panel flight uses the airspeed indicator, turn and slip indicator, or turn coordinator, and
clock to keep the aircraft straight and level and to maneuver it. Partial-panel flight assumes the attitude
gyro and horizontal situation indicator (or gyro horizon and directional gyro) to be inoperative.
partial pressure (gas pressure). The percentage of the total pressure of a mixture of gases produced by
each of the individual gases in the mixture. The atmosphere surrounding the earth is a mixture of gases of
which nitrogen makes up about 78% and oxygen 21%. If the pressure of the atmosphere is 29.92 inches
(760 mm) of mercury, the partial pressure of the nitrogen is 78% of this, or 23.33 inches (592.8 mm) of
　
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