M or mag
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
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
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
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
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
MTMA - military terminal control area.
mtow - maximum take-off weight.
mtwa - maximum total weight authorised.