aviation glossary


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.