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below aircraft are required to maintain altitude.
Maximum authorized altitude (MAA). A published altitude
representing the maximum usable altitude or flight level for
an airspace structure or route segment.
MB. See magnetic bearing.
MCA. See minimum crossing altitude.
MDA. See minimum descent altitude.
MEA. See minimum en route altitude.
Mean sea level. The average height of the surface of the
sea at a particular location for all stages of the tide over a
19-year period.
MFD. See multi-function display.
MH. See magnetic heading.
MHz. Megahertz.
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Microwave landing system (MLS). A precision instrument
approach system operating in the microwave spectrum which
normally consists of an azimuth station, elevation station,
and precision distance measuring equipment.
Mileage breakdown. A fix indicating a course change
that appears on the chart as an “x” at a break between two
segments of a federal airway.
Military operations area (MOA). Airspace established for
the purpose of separating certain military training activities
from IFR traffic.
Military training route (MTR). Airspace of defined vertical
and lateral dimensions established for the conduct of military
training at airspeeds in excess of 250 knots indicated airspeed
(KIAS).
Minimum altitude. An altitude depicted on an instrument
approach chart with the altitude value underscored. Aircraft are
required to maintain altitude at or above the depicted value.
Minimum crossing altitude (MCA). The lowest allowed
altitude at certain fixes an aircraft must cross when proceeding
in the direction of a higher minimum en route altitude
(MEA).
Minimum descent altitude (MDA). The lowest altitude (in
feet MSL) to which descent is authorized on final approach,
or during circle-to-land maneuvering in execution of a
nonprecision approach.
Minimum en route altitude (MEA). The lowest published
altitude between radio fixes that ensures acceptable
navigational signal coverage and meets obstacle clearance
requirements between those fixes.
Minimum obstruction clearance altitude (MOCA). The
lowest published altitude in effect between radio fixes on VOR
airways, off-airway routes, or route segments, which meets
obstacle clearance requirements for the entire route segment
and which ensures acceptable navigational signal coverage
only within 25 statute (22 nautical) miles of a VOR.
Minimum reception altitude (MRA). The lowest altitude
at which an airway intersection can be determined.
Minimum safe altitude (MSA). The minimum altitude
depicted on approach charts which provides at least 1,000 feet
of obstacle clearance for emergency use within a specified
distance from the listed navigation facility.
Minimum vectoring altitude (MVA). An IFR altitude lower
than the minimum en route altitude (MEA) that provides
terrain and obstacle clearance.
Minimums section. The area on an IAP chart that displays the
lowest altitude and visibility requirements for the approach.
Missed approach. A maneuver conducted by a pilot when an
instrument approach cannot be completed to a landing.
Missed approach point (MAP). A point prescribed in each
instrument approach at which a missed approach procedure
shall be executed if the required visual reference has not
been established.
Mixed ice. A mixture of clear ice and rime ice.
MLS. See microwave landing system.
MM. Middle marker.
MOA. See military operations area.
MOCA. See minimum obstruction clearance altitude.
Mode C. Altitude reporting transponder mode.
MRA. See minimum reception altitude.
MSA. See minimum safe altitude.
MSL. See mean sea level.
MTR. See military training route.
Multi-function display (MFD). Small screen (CRT or LCD)
in an aircraft that can be used to display information to the
pilot in numerous configurable ways. Often an MFD will be
used in concert with a Primary Flight Display.
MVA. See minimum vectoring altitude.
NACG. See National Aeronautical Charting Group.
NAS. See National Airspace System.
National Airspace System (NAS). The common network of
United States airspace—air navigation facilities, equipment
and services, airports or landing areas; aeronautical charts,
information and services; rules, regulations and procedures,
technical information; and manpower and material.
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National Aeronautical Charting Group (NACG). A
Federal agency operating under the FAA, responsible for
publishing charts such as the terminal procedures and en
route charts.
National Route Program (NRP). A set of rules and
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Instrument Flying Handbook仪表飞行手册下(109)
