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overhead-valve engine (type of reciprocating engine). A reciprocating engine in which the intake and
exhaust valves are located in the cylinder head. This type of engine is also called a valve-in-head engine.
overheat warning system (fire warning system). A type of warning system that warns the flight crew that
an engine nacelle or wheel well is too hot for normal operation, but there is no localized high temperature
that indicates the presence of a fire.
overinflation valve (aircraft wheel component). A valve used in some large aircraft wheels that mount
tubeless tires. The valve opens and relieves the excess pressure if the tire is accidentally overinflated.
overlying center (air traffic control). The ARTCC facility that is responsible for arrival/departure
operations at a specific terminal.
overrunning clutch. A type of clutch that couples a drive element with a driven element. When the drive
element is being rotated, the driven element rotates with it. But when the driven element is being rotated by
an outside force, the drive element does not turn.
Overrunning clutches are used in some types of aircraft engine starters. The starter rotates the
engine through the clutch, but when the engine starts and turns faster than the starter motor, the clutch
prevents the engine driving the starter.
overseas air commerce. 14 CFR Part 1: “The carriage by aircraft of persons or property for compensation
or hire, or the carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or
furtherance of a business or vocation, in commerce between a place in any State of the United States, or the
District of Columbia, and any place in a territory or possession of the United states; or between a place in a
territory or possession of the United States, and a place in any other territory or possession of the united
States.”
overseas air transportation. 14 CFR Part 1: “The carriage by aircraft of persons or property as a common
carrier for compensation or hire, or the carriage of mail by aircraft, in commerce:
(1) Between a place in a State or the District of Columbia and a place in a possession of the United
States; or
(2) Between a place in a possession of the United States and a place in another possession of the
United States; whether that commerce moves wholly by aircraft or partly by aircraft and partly by other
forms of transportation.”
oversize stud (aircraft hardware). A special stud used to replace a standard stud that has worn its hole
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 423
oversize. The thread pitch and type are the same as those of the standard stud, but the diameter of the
oversize stud is greater.
overspeed condition (propeller governor condition). The condition in which an engine is turning at a
speed greater than that selected by the governor. The upward force produced by the governor flyweights is
greater than the downward force of the speeder spring, and the governor causes the pitch of the propeller to
increase to reduce the engine speed.
overtemperature warning system. A warning system similar in many ways to a fire warning system, but
differing in that it initiates the warning signal at a lower temperature than needed for a fire warning. A high
temperature in a small area initiates a fire warning, but a lower temperature over a larger area indicates an
overtemperature condition.
over-the-top. 14 CFR Part 1: “Above the layer of clouds or other obscuring phenomena forming the
ceiling.”
overtone. A whole-number multiple of the frequency of a vibration. An overtone is the same as a harmonic.
See harmonic.
overvoltage protector (electrical circuit component). A component used to protect electrical circuits
from surges of high voltage that could cause damage. A sensor monitors the voltage and, if it becomes
excessive, the overvoltage protector opens the circuit to protect the components.
oxidation. The chemical action in which a metallic element is united with oxygen. Electrons are removed
from the metal in this process.
oxide (chemical compound). A chemical compound, such as aluminum oxide (Al2O3), that is composed
of oxygen and another element, in this case, aluminum.
oxidizing flame (oxygas welding). An oxygas welding flame in which more oxygen is supplied to the
torch than is needed for a neutral flame. An oxidizing flame is identified by a sharp-pointed inner cone and
a hissing noise made by the torch.
oxygas welding. A form of welding in which a fuel gas, such as acetylene or hydrogen, is mixed with
oxygen in the mixing chamber of a torch. When these gases are burned, they produce the large amount of
heat needed to melt the metal so it can be welded.
　
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