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should specifically request a PAR approach when a precision radar approach is desired or request an ASR,
or surveillance, approach when a nonprecision radar approach is desired.
gear. A special wheel with notched teeth on its periphery. Gears transmit power from one shaft to another
without slippage by meshing the teeth of the gear on one shaft with the teeth of the gear on the other. Gears
are used to reverse the direction of shaft rotation and to gain mechanical advantage.
gear and pinion mechanism. A mechanical force amplifying system that uses two gears of different sizes.
The smaller gear, the pinion, meshes with and turns faster than the larger gear. The ratio between the
number of teeth on the pinion and the number on the large gear determines the mechanical advantage of the
mechanism.
gear backlash. The amount of clearance between the teeth of two meshed gears. It is very important that
the correct amount of gear backlash be maintained when meshing gears. If there is no backlash, the teeth
cannot be properly lubricated, and the gears will wear excessively. If there is too much backlash, the load is
not properly transmitted from one tooth to the other.
Gear backlash is measured by holding one gear still and measuring, with a dial indicator, the
amount the meshing gear can move back and forth. Service manuals for equipment using gears specify the
amount of gear backlash required.
gear-driven supercharger (aircraft reciprocating engine component). An air compressor driven by
gears from the crankshaft of a reciprocating engine. Power is taken from the engine to drive the
supercharger, but the increase in power produced by compressing the intake air more than compensates for
the loss. Gear-driven superchargers are not as efficient as turbochargers, because the power used to drive a
turbocharger would otherwise be wasted.
geared-fan engine (aircraft gas turbine engine). A type of turbofan engine using a set of reduction gears
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 275
between the first stage of the gas generator compressor and the fan. By using reduction gears, the fan can
turn slowly enough that its tip speed is held below the speed of sound. And at the same time, the gas
generator compressor can turn at speeds high enough for it to be efficient.
geared propeller (aircraft engine). A propeller on an aircraft engine that is driven from the crankshaft
through a set of reduction gears. The engine is allowed to operate at a speed at which it is most efficient,
and the propeller turns slowly enough that its tips do not exceed the speed of sound.
gear preload. The amount of pressure applied in a gear system to keep the gears meshed.
gear-type pump. A type of power-driven pump used to move such fluids as fuel and oil. A gear-type pump
is a constant-displacement pump using two meshing spur gears, mounted in a close-fitting housing.
Fluid is taken into the housing where it fills the space between the teeth of the gears, and it is
carried around the housing as the gears rotate. On the discharge side of the pump, the gear teeth mesh, and
the fluid is forced out of the pump.
gelled cell (batteries). A type of lead-acid battery cell that has a gelling agent added to the electrolyte to
make it nonspillable. Gelled-cell batteries are used for portable operations.
genemotor (electrical machine). A type of electrical machine used to change low-voltage direct current
from a storage battery into high-voltage DC for operating some types of communications equipment. A
genemotor has two armatures on a single shaft. One armature and one set of field coils are for the DC
motor. The other armature and set of field coils are for the high-voltage generator. Genemotors are also
called dynamotors.
general aviation. A term used to describe the total field of aviation operation other than the military and
the airlines. General aviation includes business flying (corporate, or executive), agricultural aviation,
personal flying for sport or pleasure, flight schools, and flying clubs. The manufacturers of the aircraft and
the maintenance facilities that service them are also a part of general aviation.
general aviation district office. See GADO.
General Aviation Airworthiness Alerts. Documents furnished by the FAA to technicians alerting them of
problems that have been found in specific models of aircraft, and reported on Malfunction and Defect
Reports. Airworthiness Alerts suggest corrective action, but compliance with the suggestion is not
mandatory. Alerts include items that have been reported to be significant, but which have not been fully
evaluated at the time the material went to press. See Malfunction and Defect Report.
general gas law. A single law that combines the laws of Boyle and Charles to explain the relationship
　
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