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low unmetered fuel pressure. The pressure in a Teledyne-Continental fuel injector pump that is adjusted
by the relief valve.
LOX. The abbreviation for liquid oxygen. See liquid oxygen.
LR circuit (electrical circuit). An alternating current circuit containing inductance (L) and resistance (R).
The total opposition to the current in an LR circuit is impedance (Z), which is the vector sum of the
inductive reactance and the resistance.
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LRU (line replaceable unit). Components in an aircraft that are designed so that they can be replaced as a
unit while the aircraft is on the flight line.
LSB (least significant bit). The bit in a binary number that has the lowest place value. The LSB is the bit
on the extreme right.
LSD (least significant digit). The digit in a decimal number that has the lowest place value. The LSD is
the digit on the extreme right.
LSI (large scale integration). A method of miniaturization of electronic circuit components, in which 100
or more gates are built into a single integrated circuit (IC) chip. LSI techniques lower the cost per gate of
logic components.
lubber line. The reference line used in a magnetic compass or directional gyro, to indicate the nose of the
aircraft. The heading of the aircraft is shown as the degrees on the card or dial of the instrument opposite
the lubber line.
lubricant. A natural or synthetic material used to reduce the friction between parts in sliding contact with
each other. Even parts that seem to be smooth actually have microscopically rough surfaces. When one
rough surface slides over another, the surfaces lock and oppose the movement (this is called friction).
A lubricant between the surfaces holds them apart, and they slide over a film of the lubricant,
rather than over each other. Lubricants may be in the form of a dry powder (powdered graphite or
molybdenum), a liquid (oil), or a semi-liquid (grease).
Lucite. The registered trade name for a transparent acrylic resin. Lucite is a thermoplastic resin, used for
windshields and side windows of some aircraft.
luminance. The amount of light emitted or scattered by a surface. Luminance is measured in lamberts.
luminescence. The production of light by some method other than incandescence (light emitted because of
high temperature). Luminescence may be caused by friction, chemical action, or electrical charges, and
regardless of the method of luminescence, the light produces little or no heat.
luminous paint. A type of paint having components that cause it to emit light, or glow in the dark. Radium
was, at one time, the main component in luminous paint. But because of its harmful characteristics, it has
been replaced by other materials. Luminous paint is used on instrument dials and pointers to make them
visible in the dark.
lutetium. A silvery-white, rare-earth chemical element. Lutetium’s symbol is Lu, its atomic number is 71,
and its atomic weight is 174.97. Lutetium is the heaviest of the rare-earth elements and is used in nuclear
technology.
lye. A strong alkaline solution made of potassium hydroxide or sodium hydroxide.
M
MAA (maximum authorized altitude). A published altitude representing the maximum usable altitude or
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flight level for an airspace structure or route segment. MAA is the highest altitude on a Federal airway, jet
route, area navigation low or high route, or other direct route for which an MEA is designated in 14 CFR
Part 95, at which adequate reception of navigation aid signals is assured.
MAC (mean aerodynamic chord). The chord of an imaginary airfoil that has the same aerodynamic
characteristics as the actual airfoil. The length of the MAC is given for many aircraft, and the CG is
expressed in percent of the mean aerodynamic chord (% MAC).
Mach cone. The cone-shaped shock wave produced by a sharp-pointed object moving through the
atmosphere at a speed greater than the speed of sound.
machine bolt. The common name for a hex-head bolt.
machine language (computer operation). A language, made up of zeros and ones, that is usable by a
digital computer. Machine language is difficult to write into a computer, so compilers and assemblers are
used. A compiler is a special program that converts a high-level language that is easy for a programmer to
use, into machine language that can be used by the computer. An assembler converts assembly language
programs into machine language the computer can use.
machine screw. A blunt-end screw with uniform threads that can be screwed into a tapped hole or a nut. A
machine screw is turned with a screwdriver and may have a round, flat, truss, oval, or fillister head.
　
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