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to the BOTH position before the engine stops turning. This safety check assures that both magnetos are
grounded when the switch is in the OFF position.
magnetosphere. The outer layer of the earth’s atmosphere. The magnetosphere starts about a thousand
miles above the earth and is the beginning of interplanetary space. The magnetic field of the earth traps
charged particles in the magnetosphere.
magnetostriction. The characteristic of certain ferromagnetic materials (magnetic materials containing iron)
that causes them to change their physical size when they are subjected to a magnetic field. Magnetostriction
is used in some types of transducers (devices that change electrical signals into physical movement).
If a bar of magnetostrictive material is used as the core of a coil through which alternating current
is flowing, the changing magnetic field produced by the AC causes the magnetostrictive bar to change its
size enough that it will vibrate an object attached to it.
magnetron. A special electron tube used to produce high-power electromagnetic energy in the ultrahigh
and superhigh frequency ranges. Magnetron tubes are used in airborne radar equipment.
magnet wire. The common name for small diameter, varnish-insulated, annealed copper wire. Magnet wire
is used for winding coils for electromagnets, transformers, motors, and generators.
magnitude of a force. A quantitative measure of the amount of a force.
main rotor. 14 CFR Part 1: “The rotor that supplies the principal lift to a rotorcraft.”
maintenance. The upkeep of equipment. Mechanical and electrical equipment must be periodically
inspected, to be sure it performs as it was designed and built to perform. When it begins to fail, correct
maintenance will usually prevent the problem becoming major. In addition to inspection, maintenance
includes adjustments, lubrication, and the replacement of parts to keep the equipment operating as it should.
14 CFR Part 1: “Inspection, overhaul, repair, preservation, and the replacement of parts, but excludes
preventive maintenance.”
maintenance checks (letter checks). A classification of maintenance inspections or checks used in airline
operation.
A-check. A thorough visual inspection and an operational check of all major systems of the
airframe and engine.
B-check. A complete A-check and a more detailed check of certain systems specified for the
particular aircraft.
C-check. Complete A and B checks with more in-depth inspection of certain systems. A C-check
may include a flight check.
D-check. The most in-depth inspection of the aircraft. It requires removal of such components as
engines and landing gear.
maintenance manual. A set of detailed instructions issued by the manufacturer of an aircraft, engine, or
component that describes the way maintenance of the device should be performed. Maintenance manuals
for certificated aircraft and their components are approved by the Federal Aviation Administration and may
be used as approved data when making repairs.
maintenance release. A release, signed by an authorized inspector or AMT, signifying that an aircraft has
been approved for return to service after certain maintenance functions have been completed. It is also a
statement made by an Approved Repair Station in lieu of a Form 337 that approves a product for return to
service after a major repair.
major alteration (aircraft alteration). 14 CFR Part 1: “An alteration not listed in the aircraft, aircraft
engine, or propeller specifications —
(1) That might appreciably affect weight, balance, structural strength, performance, power-plant
operation, flight characteristics, or other qualities affecting airworthiness; or
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 371
(2) That is not done according to accepted practices or cannot be done by elementary operations.”
major axis of an ellipse. A line passing through the two focuses of an ellipse. See ellipse.
major diameter (threaded fastener). The diameter of the threads of a bolt or screw measured at the crests
(the tops) of the threads.
majority carriers (semiconductor material). The main electrical carriers within a semiconductor material.
The majority carriers in P-type material are holes, and in N-type material, electrons.
major overhaul (engine overhaul). The disassembly, cleaning, and inspection of an engine and the repair
and replacement of all parts that do not meet the manufacturer’s specifications. After all of the inspections
and repairs are made, the engine is reassembled and tested according to the manufacturer’s instructions.
Major overhaul restores an engine to a serviceable condition, and it normally operates as though it were
　
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