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conductors. PCs have almost completely replaced the older point-to-point wired circuits.
priority valve (fluid power system component). A type of flow-control valve used in a fluid power
system that causes the components to operate in the correct sequence. Priority valves are used in an aircraft
hydraulic system to cause the landing gear doors to open fully before the uplocks release the landing gear.
PRM (precision runway monitor) (air traffic control). A monitor that provides air traffic controllers
with high-precision secondary surveillance data for aircraft on final approach to closely spaced parallel
runways. High-resolution color monitoring displays present surveillance track data to controllers, along
with detailed maps depicting approaches and the no transgression zone.
procedure turn (air traffic control). The maneuver prescribed when it is necessary to reverse direction to
establish an aircraft on the intermediate approach segment or final approach course. The outbound course,
direction of turn, distance within which the turn must be completed, and minimum altitude are specified in
the procedure. However, unless otherwise restricted, the point at which the turn may be commenced and the
type and rate of turn are left to the discretion of the pilot.
product (mathematics). The answer in a multiplication problem.
Production Certificate. A certificate issued under 14 CFR Part 21 that allows a certain certificated aircraft,
aircraft engine, or appliance to be manufactured by the specified facility.
profile descent (air traffic control). An uninterrupted descent (except where level flight is required for
speed adjustment; e.g., 250 knots at 10,000 feet MSL) from cruising altitude or flight level to the
interception of a glideslope or to a minimum altitude specified for the initial or intermediate approach
segment of a nonprecision instrument approach. The profile descent normally terminates at the approach
gate where the glideslope or other appropriate minimum altitude is intercepted.
profile drag (aerodynamic drag). Aerodynamic drag caused by friction between the air and the surfaces
of an aircraft over which it is flowing. Profile drag is one of the forms of parasite drag.
profile tip (turbine engine compressor blade tip). An axial-flow compressor blade whose tip thickness is
reduced to give it a higher resonant frequency so it will not be subject to the vibrations that would affect a
blade with a squared tip. The profile tip also provides a more aerodynamically efficient shape for the
high-velocity air that is moved by the blade. Profile tips often touch the housing and make a squealing
noise as the engine is shut down. For this reason, profile tips are sometimes called squealer tips.
profilometer. A precision measuring instrument used to measure the depth of the hone marks in the surface
of an aircraft engine cylinder wall.
prognostic chart (meteorology). A chart showing expected or forecast weather conditions. Prognostic
charts are generally referred to as prog charts.
program (computer operation). A series of step-by-step instructions that tells a computer exactly how it
is to receive data, store it, process it, and deliver it to the user.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 461
program flowchart (computer operation). A chart of the steps taken in the execution of a program by a
computer. Symbols are used in the flowchart to show the beginning and the end of the program, data input
and output points, and decision points.
programmable calculator. An electronic calculator controlled by a program stored in its memory. A
programmable calculator is a versatile instrument that allows the use of different programs to solve many
different types of problems.
programmable read-only memory. See PROM.
progressive inspection (aircraft maintenance inspection). An inspection that may be used in place of an
annual or 100-hour inspection. It has the same scope as an annual inspection, but it may be performed in
increments so the aircraft does not have to be out of service for a lengthy period of time.
progressive taxi (air traffic control). Precise taxi instructions given to a pilot unfamiliar with the airport
or issued in stages as the aircraft proceeds along the taxi route.
PROM (programmable read-only memory). An integrated circuit memory device for a digital computer.
Read-only memory is stored in PROM as a series of logic zeros and ones, by burning out certain diodes in
it. Once the PROM is programmed, it cannot be changed.
There is an erasable, programmable read-only memory (EPROM) that can be erased by exposing
it to ultraviolet light. It can then be reprogrammed by using a special programmer.
prohibited area. 14 CFR Part 1: “Designated airspace within which flight of aircraft is prohibited.”
　
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