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mercury, and the partial pressure of the oxygen is 21% of the total or 6.28 inches (159.6 mm) of mercury.
parting compound (composition materials fabrication). A material spread on a mold before plastic resin
is put into it. The parting compound keeps the resin from sticking to the mold. Parting compound is
sometimes called a parting agent.
parting film. A layer of thin plastic material that is placed between a composite lay-up and the heating
blanket. It prevents the blanket sticking to the fabric.
part number (aircraft parts identification). The number assigned by the aircraft manufacturer to identify
a particular aircraft part. The part number is normally the same as the drawing number for the part.
parts list (aircraft drawing). A list of all items and their part numbers that are included on an assembly
drawing. A parts list is also called a Bill of Materials.
Parts Manufacturer Approval. See PMA.
pascal. The unit of pressure in the metric system that is produced when one newton of force acts uniformly
over an area of one square meter. One pascal is equal to 14.503 • 10-5 (0.000 145 03) psi. The kilopascal
(kPa) is easier to manipulate. 1 kPa = 1,000 Pa = 0.14503 psi. The pascal is named after the French
mathematician Blaise Pascal, who was born in 1623.
Pascal’s law (physics law). A basic law of physics which states that pressure built up in an enclosed
container of fluid is transmitted equally and undiminished to all parts of the container, and this pressure
acts at right angles to the walls of the container.
passenger mile. A measure of the amount of travel provided by an airline, steamship line, or railroad. One
passenger mile is the carriage of one passenger for one mile.
passivation (corrosion protection). A method of protecting aluminum or magnesium alloys from
corrosion. Passivation consists of forming a hard, tight oxide film on the surface of the metal by chemical
action.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 429
passive component (electrical component). A component that produces no gain in an electrical circuit.
Resistors, capacitors, and inductors are passive components. Active components are such devices as
transistors and electron tubes that do produce current or voltage gain.
passive electrical circuit. An electrical circuit that does not contain any source of electrical energy. A
passive circuit depends upon an active circuit for its power.
passive satellite. A satellite that reflects but does not amplify or change communications signals from the
ground or other satellites.
passive sonar. An acoustic underwater detection system that listens for the sound produced by underwater
objects. Passive sonar does not transmit signals to search for submerged objects.
patent certificate. A legal document giving a person the exclusive right to own a particular device. When a
person invents something, the rights of ownership are protected by patenting the device. A search is made
by the patent office to be sure no one has patented the same device at an earlier time. If no earlier patent is
recorded, the person applying for the patent is issued a patent certificate.
pattern (flight operation). A published description of the flight paths aircraft must follow when
approaching an airport for landing and when leaving the airport after taking off. All aircraft following the
same flight pattern minimizes the danger of in-flight collision.
pattern (metal molding). A model used to form the mold into which molten metal is poured to cast a
metal part. Patterns are usually made of wood, and are made with allowance for the dimensional changes
that take place when the metal cools and turns into a solid from its molten state.
PATWAS (Pilots Automatic Telephone Weather Answering Service). A continuous telephone
recording containing current and forecast weather information for pilots.
pawl (ratchet device). A driving or holding link used in a ratchet mechanism. The pawl allows a ratchet
wheel to turn in one direction, but keeps it from turning in the opposite direction.
payload. The amount of load carried by a vehicle over and above the load necessary for the operation of
the vehicle. Payload is actually the amount of revenue-producing load an aircraft can carry.
P-band radar. Radar that operates in the frequency range between 225 and 390 megahertz. At this
frequency, the wavelengths of the pulses of energy are between 133.3 and 76.9 centimeters.
PCB (plenum chamber burning). A method of thrust augmentation used on engines with vectored
nozzles. Fuel injected into the fan discharge air is burned to increase thrust.
P-channel field effect transistor. A field effect transistor having a source, drain, and channel of P-material
　
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