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dedicated departure runway(s) for arrivals, when feasible to reduce delays and enhance capacity.
multiplex (method of communications). Multiplex transmission is a method of two-way communications
in which both stations can transmit at the same time on the same frequency or on the same line. Normal
telephone communications is an example of multiplex communications. Both parties can talk on the same
line at the same time.
multiplicand (mathematics). The number in a multiplication problem that is multiplied by another number.
In the problem 4 • 2 = 8, the number four is the multiplicand.
multiplier (mathematics). The number in a multiplication problem that is used to multiply another number.
In the problem 4 • 2 = 8, the number two is the multiplier.
multiplier resistor. A resistor in series with a voltmeter mechanism used to extend the range of the basic
meter or to allow a single meter to measure several ranges of voltage.
multispar wing (aircraft structure). A type of airplane wing construction that uses several small spars
extending along the span of the wing to carry the structural loads. Multiple small spars carry the load better
and weigh less than the two larger spars used in many aircraft wings.
multivibrator (electronic circuit). A type of oscillator in which there are two active devices (transistors or
electron tubes) which alternate in conducting. Multivibrators may be free running, bistable, or monostable.
A free-running multivibrator automatically switches back and forth between the devices and continues to
do this as long as power is supplied.
In a monostable multivibrator, one device is normally conducting, but a pulse on its base or grid
will switch it off and the other one on. As soon as the pulse is removed, the conduction is switched back to
the first.
In a bistable multivibrator, either device conducts equally well. A pulse on the base or grid of the
first device turns it off and causes the second one to conduct until it receives a pulse on its base or grid. It
then turns off, and conduction reverts back to the first.
mumetal. An alloy having a high magnetic permeability used to make magnetic shields. Mumetal is an
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 395
alloy of 14% iron, 5% copper, 1.5% chromium, and 79.5% nickel.
muriatic acid. A form of commercial hydrochloric acid (HCl). One of the popular uses for muriatic acid is
as a flux for cleaning metal in preparation for soldering.
mushroomed head (damaged tool head). A damaged head on a chisel or punch caused by hammering on
the tool. Mushroomed heads are dangerous, because a piece of the metal can be easily broken off and cause
injury. A mushroomed head must be ground off of a tool as soon as it forms.
mutual induction. The cause of a voltage being induced in one circuit by a changing current in another
circuit when there are no electrical connections between the two. Changing current causes lines of magnetic
flux to expand and contract. When this changing flux cuts across the conductors in another circuit, mutual
induction causes a voltage to be induced in it.
MVA (minimum vectoring altitude) (air traffic control). The lowest MSL altitude at which an IFR
aircraft will be vectored by a radar controller, except as otherwise authorized for radar approaches,
departures, and missed approaches.
The altitude meets IFR obstacle clearance criteria, and it may be lower than the published
minimum en route altitude (MEA) along an airway or J-route segment. It may be utilized for radar
vectoring only upon the controller’s determination that an adequate radar return is being received from the
aircraft being controlled. Charts depicting minimum vectoring altitudes are normally available only to the
controllers and not to pilots.
Mylar. The registered trade name for a polyester film widely used as an electrical insulator and as a
packaging material. Mylar is also used as a film on which high quality ink drawings can be made.
Mylar capacitor. A nonelectrolytic capacitor that uses strips of metal foil as the plates and Mylar film as
the dielectric.
N
N1. A symbol representing the rotational speed of the low-pressure compressor in a dual-spool gas turbine
engine. In common usage, the low-pressure compressor is often called the N1 compressor.
N2. A symbol representing the rotational speed of the high-pressure compressor in a dual-spool gas turbine
engine. In common usage, the high-pressure compressor is often called the N2 compressor.
N3. A symbol representing the rotational speed of the high-pressure compressor in a triple-spool gas
turbine engine.
NACA (National Advisory Committee for Aeronautics). This organization was dedicated to the
　
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