the Aviation Dictionary

platinum spark plug . point-to-point wiring
extremely high melting point and is used for the
electrodes of fine-wire spark plugs.
. .-
platinum spark plug - A fine-wire electrode spark plug
that can operate at very high temperatures.
play - The relative movement between parts. Play is the
amount of movement that occurs in a cockpit flight
control before the associated flight surface to move.
P-lead - The primary lead of an aircraft magneto.
Connected to the ignition switch.
plenum - An enlargement of a duct or an enclosing
space in an aircraft engine induction system or air
conditioning system. Used to smooth out the pulsations
in the flow of the air.
plenum chamber - An enclosed volume of air in which
the air is held at a slightly higher pressure than that of
the surrounding air.
Plexiglas - A transparent acrylic plastic material used
for aircraft windshields and side windows.
pliers - Small, pincher-like hand tools used for holding
small objects or for bending and cutting wire.
plies - Sheets of material that are laminated together.
plumb - A weight attached to a line or string and used
to indicate vertical direction. Anything that lines up
with the plumb line is said to be plumb or in plumb.
plumb bob - A weight attached to a line or string and
used to establish a location directly below the point to
which the line is attached.
plumb line - The straight line of a string to which a
plumb bob is attached and hung. Anything that lines up
with the plumb line is said to be plumb or in plumb.
plumbing - Tubing and fittings or connectors used for
transmitting - fluid within a structure or piece of
equipment.
plumbing connection - Threaded connections that join
sections of tubing, or which are used to connect the
tubing to a component.
plunger - A part of a machine that works with a
relatively rapid downward motion.
plutonium - A radioactive metallic element with the
symbol Pu and an atomic number of 94.
ply - In composites, one layer of reinforcement in a
laminate.
ply rating - A load rating for aircraft tires that relates to
the strength of cotton plies. For example, a 20-ply
rating nylon tire has the same load rating as a tire with
20 cotton plies.
plywood - Layers of wood glued together so that the
grain in each layer is placed 45" or 90" to the others.
PN Junction - In semiconductor devices, a PN junction
is fabricated from a single slice of semiconductor with
one side doped as p-type and the other side doped as
N-type. In operation, the migration of electrons to the P
side and the holes to the N side creates a depletion area
that resists further migration of ions. he flow of
current is then controlled by the types of voltage
applied to the ends of the device.
pneudraulic - A combination of air and hydraulic
pressure.
pneumatic altimeter - An altimeter that measures
height above a given pressure level. Its calibration is
based on a specified lapse rate or change in pressure
with height.
pneumatic drill motor - An air motor equipped with a
chuck to hold twist drills.
pneumatic fire detection system - A system that uses a
gas-filled continuous tube. The gas expands when
heated and acts on a diaphragm to close an electrical
A -
circuit and show a warning light in the cockpit.
pneumatic starter - Starting motor operated by air
pressure.
pneumatic system - The power system in an aircraft
used for operating landing gear, brakes, wing flaps, etc.
with compressed air as the operating fluid.
pneumatic-mechanical fuel control - A fuel control
that utilizes pneumatic and mechanical forces to
operate its fuel scheduling mechanisms.
pneumatics - The system of fluid power that transmits
force by the use of a compressible fluid.
PNP transistor - The three-element semiconductor
device made up of a sandwich of N-type silicon or
germanium between two pieces of P-type material.
pod - An enclosure housing a complete engine
assembly.
pogonip - A dense winter fog containing frozen
particles. Forms in deep mountain valleys.
point out - An action taken by a controller to transfer
the radar identification of an aircraft to another
controller if the aircraft will or can enter the airspace or
protected airspace of another controller and radio
communications will not be transferred. Also referred
to as radar point out.
pointer - A thin strip of movable metal moved over a
calibrated scale by an analog instrument mechanism.
Also referred to as hands or needles.
point-to-point wiring - An antiquated method of
building electronic units. Electronic components were
mounted directly on the chassis and interconnected by
means of wires that were integral parts of the
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