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heated to a temperature lower than that used for the initial heat treatment. It is held at this temperature for a
specified period of time and then removed from the oven and allowed to cool slowly. Precipitation heat
treatment is also known as artificial aging.
precipitation static (radio interference). A form of radio interference caused by rain, snow, or dust
particles hitting the antenna and inducing a small radio-frequency voltage into it.
precision approach. 14 CFR Part 1: “A standard instrument approach procedure in which an electronic
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 455
glide slope is provided, such as ILS and PAR.”
precision approach radar. See PAR.
precision switch (electrical component). A snap-action switch that requires a very small amount of
movement for its actuation. The amount of movement needed is the same each time the switch is actuated.
Precision switches are used in position-indicating circuits and as limit switches to start or stop an action any
time a mechanical device reaches a specific position.
preferential routes (air traffic control). Preferential routes are adapted in ARTCC computers to
accomplish inter/intrafacility controller coordination and to assure that flight data is posted at the proper
control positions.
Locations having a need for these specific inbound and outbound routes normally publish such
routes in local facility bulletins, and their use by pilots minimizes flight plan route amendments. When the
workload or traffic situation permits, controllers normally provide radar vectors or assign requested routes
to minimize circuitous routing. Preferential routes are usually confined to one ARTCCs area and are
referred to by the following names or acronyms:
• Preferential departure route (PDR).
• Preferential arrival route (PAR).
• Preferential departure and arrival route (PDAR).
preferred IFR routes (air traffic control). Routes established between busier airports to increase system
efficiency and capacity. Preferred IFR routes normally extend through one or more ARTCC areas and are
designed to achieve balanced traffic flows among high density terminals. IFR clearances are issued on the
basis of these routes except when severe weather avoidance procedures or other factors dictate otherwise.
Preferred IFR routes are listed in the Airport/Facility Directory.
If a flight is planned to or from an area having such routes but the departure or arrival point is not
listed in the A/FD, pilots may use that part of the preferred IFR route which is appropriate for the departure
or arrival point that is listed. Preferred IFR routes are correlated with SIDs and STARs and may be defined
by airways, jet routes, direct routes between navaids, waypoints, navaid radials/DME, or any combination
of these items. See SID, STAR.
preferred values (electrical components). A series of values for resistors and capacitors, selected by the
Electronic Industries Association (EIA) and the military services. The steps between the values are chosen,
so the difference between any two steps is essentially the same percentage as the difference between any
other two steps. The use of preferred values allows the most complete coverage of the needed values, with
a minimum number of components.
preflight inspection (aircraft inspection). An inspection of an aircraft performed by the pilot or flight
engineer before the aircraft is approved for flight. The purpose of a preflight inspection is to assure that the
aircraft is in a safe condition for the flight being proposed.
preformed cable (aircraft control cable). A type of steel cable used in aircraft control systems. Preformed
cable is made up of seven bundles (strands) of wires wound together to form the complete cable. Each
strand is formed into a spiral (preformed) before the cable is wound. Because each strand is preformed, the
cable does not spread out when it is cut.
preignition (reciprocating engine malfunction). Ignition of the fuel-air mixture inside the cylinder of an
engine before the normal spark occurs. Preignition can be caused by an incandescent piece of carbon or by
any other sharp edge or point inside the cylinder that gets red-hot.
preoiling (engine installation). A step in the installation of a new or overhauled engine in an aircraft.
Lubricating oil is pumped through the oil passages in the engine, so all the bearing surfaces will be flooded
with oil when the engine starts.
prepreg (preimpregnated fabric). A type of composite material in which the reinforcing fibers are
encapsulated in an uncured resin. Prepreg must be kept refrigerated to prevent the resin curing before it is
used. Prepreg materials are cut to size and shape and laid up with the correct ply orientation, and the entire
　
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