Aviation Glossary - M
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M or mag - magnetic
Mach number - ratio of true airspeed to the speed of sound.
Mach 1 is the speed of sound at sea level, ISA, approximately
1,100 feet per second or 760 mph.
MAP - missed approach point. The point on a published ILS
approach expressed in time or distance from the final approach
fix, or as an altitude on the glideslope, at which the missed
approach procedure must be initiated if the runway or approach
lights are not clearly in sight.
marker beacons (mkrs) - part of an instrument landing system
using 75 MHz transmitters emitting fan-shaped or elliptical
signal patterns vertically upwards, defining specific points
along the glideslope. The outer marker OM is situated at
or near the glideslope intercept altitude of the ILS localiser,
the middle marker (MM) defines a point on the glideslope
at or near decision height (DH). Markers provide aural and
visual indications on a cockpit marker beacon receiver.
MATZ - military aerodrome traffic zone. An area of protected
airspace surrounding certain military airfields which normally
extends for a five nautical mile radius around the airfield
and upwards from the surface to 3,000 feet above aerodrome
level. A 'stub' projection protects the final approach path
to the main runway outwards from the MATZ boundary, enclosing
an area two nautical miles either side of the extended runway
centreline and upwards from 1,000 feet above the surface
to 3,000 feet above aerodrome elevation. Although recognition
of a MATZ is not mandatory for civil aircraft, all MATZ
aerodromes offer a penetration service to civil traffic
during operational hours.
Mayday - international radio distress call (from the French,
m'aidez help me). It signifies imminent danger to life requiring
immediate assistance.
mb - millibar.
MCU - management control unit
MDA - minimum descent altitude. The lowest altitude, in
feet amsl, to which descent is authorised on final approach
during a non-precision instrument landing (i.e. where no
glideslope guidance is given) without visual reference to
the runway.
MDH - minimum descent height, agl.
MEDA - military emergency diversion airfield.
medevac - medical evacuation
Met - meteorology, weather.
METAR - coded aerodrome Met report. Also SPECI, special
civil aviation weather report, and TAF, terminal aerodrome
forecast of weather expected.
MF - medium frequency. Radio waves with frequencies in
the 300- 3,000 kHz range.
MFA - military flying area
MFD - multi-function display. An EFIS CRT offering selectable
displays of weather radar, navigation maps, checklists and
data other than primary flight information.
MH - magnetic heading
MHz - Megahertz, the frequency of radio carrier waves measured
in millions of cycles per second.
minimums - weather condition requirements for a particular
mode of flight (e.g. for VFR operation, IFR take-offs and
landings).
MLS - microwave landing system. A microwave-based instrument
approach system intended to replace ILS in the 1990s and
claimed to offer a number of advantages such as the ability
to fly segmented and curved precision approaches.
mlw - maximum landing weight.
MMARS - Military Middle Airspace Radar Service, available
to military and civil aircraft operating in UK airspace
between FL100 and FL245.
MOA - military operations area.
MoD - UK's Ministry of Defence
mod - modification to an aircraft or equipment
mogas - car fuel, approved for use in some light aircraft
subject to certain conditions.
MPA - man-powered aircraft
MPI - major periodic inspection
MSA - minimum sector altitude or minimum safe altitude.
msl - mean sea level
MTBF - mean time between failures. Also MTTR, mean time
to repair
MTMA - military terminal control area.
mtow - maximum take-off weight.
mtwa - maximum total weight authorised.
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