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lost communications. Loss of the ability to communicate by radio. Aircraft in this condition are sometimes
referred to as NORDO (no radio). Standard pilot procedures for lost communications are specified in 14
CFR Part 91.
lost-wax casting. A method of casting such components as turbine blades. A highly polished internal
cavity is made in the die, having the exact inverse shape of the finished part, and a special molten wax is
injected into it to completely fill the cavity. When the wax solidifies, it is removed from the die.
Several of the wax patterns are assembled on a wax gating tree, which is then dipped into a liquid
ceramic slurry a number of times until a ceramic coat about a quarter of an inch thick builds up. The
resulting ceramic mold is fired at a temperature of about 1,000°C, which melts the wax out and prepares the
mold for the next steps. The extremely hot mold is filled with the blade alloy which has been melted in an
induction furnace. After the metal has cooled, the mold is removed and the blades are cleaned and
inspected.
louver. A slotted opening in a structure, used for the passage of cooling air. Louvers are often fitted with
vanes to control the amount of air flowing through them.
low (meteorology). An area of low barometric pressure, with its attendant system of winds. A low is also
called a barometric depression or cyclone.
low altitude airway structure. The network of airways serving aircraft operations, up to, but not including,
18,000 feet MSL.
low-altitude alert system. See LAAS.
low approach. An approach over an airport or runway following an instrument approach or a VFR
approach, including the go-around maneuver in which the pilot intentionally does not make contact with
the runway.
low-bypass engine. A turbofan engine whose bypass ratio is less than 2:1. See bypass ratio.
low-frequency radio waves. Electromagnetic waves with frequencies between 30 and 300 kilohertz.
Low-frequency radio waves have wavelengths between 10,000 and 1,000 meters.
low-lead 100-octane aviation gasoline. A type of aviation gasoline having an octane rating of 100, but
containing a maximum of two milliliters of tetraethyl lead per gallon. Normal, or high-lead, 100-octane
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 362
aviation gasoline is allowed to have as much as 4.6 milliliters of lead per gallon, and this additional lead
fouls the spark plugs of engines designed to use fuel with a lower lead content. Low-lead 100-octane
aviation gasoline is dyed blue to distinguish it from normal 100-octane aviation gasoline which is dyed
green.
low-oxygen concentration cell corrosion. Corrosion that forms between the lap joints of metal and under
labeling tape, tabs or placards that trap and hold moisture. Moisture on the surface of the metal absorbs
oxygen from the air, and the extra oxygen causes the water to attract electrons from the metal to form
negative hydroxide ions. Moisture trapped in the lap joints does not have any extra oxygen and therefore
does not form any negative ions.
Since the metal in the lap joints has not given up any electrons, it is more negative than the metal
around it, and it becomes the anode in a corrosion cell and forms a salt of the metal — it corrodes.
low-pass filter (electronic filter). A type of electronic filter that passes all frequencies of alternating
current below a certain frequency, but blocks or attenuates all higher frequencies.
low-pressure compressor (gas turbine engine component). The first-stage compressor in a dual-spool
gas turbine engine. The low-pressure compressor is called the N1 compressor and its speed is not governed.
It seeks its own best speed as the atmospheric conditions change so it can furnish the optimum mass of air
to the inlet of the second-stage compressor.
low-pressure oxygen system. A gaseous oxygen system in which the oxygen is carried in steel cylinders
under a pressure of approximately 450 psi. Low-pressure oxygen systems were used in military aircraft
during World War II, but these systems have been replaced by high-pressure systems or liquid oxygen
(LOX) systems.
low-tension ignition system. A type of magneto ignition system designed for reciprocating engines that
operate at high altitude. The coil in a low-tension magneto has only one winding, the one that compares
with the primary coil in a high-tension magneto. A carbon-brush-type distributor directs the low voltage
from the magneto to the proper cylinder.
Each spark plug has its own step-up transformer, to change the low distributor voltage to the high
voltage needed to jump the gap in the spark plug. Low-tension ignition systems are not popular today
because most aircraft that fly at high altitudes are turbine powered.
　
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