- M -

MACH - A number representing the ratio of the speed of an object to the speed of sound in the surrounding air or medium in which it is moving.

MAGNETIC VARIATION - Difference between true north and magnetic north, varying with position.

MAGNETIC HEADING - Heading of the aircraft relative to magnetic north.

MAIN ROTOR - The rotor that supplies the principal lift to a rotorcraft.

MALS - medium intensity approach light system.

MALSR - medium intensity approach light system with runway alignment indicator lights.

MAINTENANCE - Inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.

MAJOR ALTERATION - 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 (2) That is not done according to accepted practices or cannot be done by elementary operations.

MAJOR REPAIR - (1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, power plant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations.

MANIFOLD PRESSURE - Absolute pressure as measured at the appropriate point in the induction system and usually expressed in inches of mercury.

MARKER BEACON - Part of Instrument Landing System that signals crew members of distance to runway, consisting of three markers: inner, middle, and outer.

MASTER CAUTION - A signal which indicates that one or more caution lights has been activated.

MASTER WARNING - A signal which indicates that one or more warning lights has been activated.

MAXIMUM PAYLOAD - Maximum Zero Fuel Weight minus Basic Operating Weight.

MAYDAY - The international radiotelephony distress signal. When repeated three times, it indicates imminent and grave danger and that immediate assistance are requested.

Mean Sea Level (MSL) - The average height of the surface of the sea for all stages of the tide.

MB - Marker Beacon.

MCA - Minimum Controllable Airspeed. The speed below which your control surfaces do not generate sufficient lift to control the aircraft.

MDA - Minimum Descent Altitude.

MEA - Minimum Enroute Altitude.

MEDICAL CERTIFICATE - Acceptable evidence of physical fitness on a form prescribed by the Administrator.

MEL - Minimum Equipment List.

METAR - Meteorological Actual Report (current weather).

MFD - Multi Function Display.

MH - Magnetic Heading.

MHZ - Megahertz (1`000 kHz).

MIDDLE MARKER (MM) - Marker beacon located where the center of the glide slope is 200 ft. above the runway.

MILITARY OPERATIONS AREA (MOA) - Airspace established outside Class A airspace to separate or segregate certain nonhazardous military activities from IFR Traffic and to identify for VFR traffic where these activities are conducted.

MINIMUM DESCENT ALTITUDE (MDA) - The lowest altitude specified in an instrument approach procedure, expressed in feet above mean sea level, to which descent is authorized on final approach or during circle-to-land maneuvering until the pilot sees the required visual references for the heliport or runway of intended landing.

MINOR ALTERATION - An alteration other than a major alteration.

MINOR REPAIR - A repair other than a major repair.

MIXTURE - Fuel to air mixture is determined by the needle valve on the engine carburetor.

MLS - Microwave Landing System.

MODE A - A transponder which does not give the controllers altitude information.

MODE C - A transponder and encoding altimeter which together give air traffic controller's altitude information.

MODE S - A transponder which features unique identification per unit, the potential for low-speed up and down data links, and "selective interrogation" triggered by ground facilities.

MOGAS - Motor Gasoline (Auto-Gas).

MOH - Major overhaul.

MRW- Maximum Ramp Weight.

MSA - Minimum Safe Altitude.

MTOW - Maximum Take-Off Weight.

MULTI-MODE RADAR (MMR) - A Multi-Mode Radar is used for Terrain Following (TF) and Terrain Avoidance (TA), Ground Mapping (GM) and Air-to Ground Ranging (AGR). The TF mode supplies commands which are processed and displayed as climb/dive commands on the Flight Director Display and E-squared video used by the operators in anticipating near term TF commands. When in TA or GM modes, the operator is provided with a Plan Position Indicator (PPI) display. The AGR mode allows the operators to determine the range to a designated target, which can be used for position updates.

MULTIFUNCTION DISPLAY (MFD) - The third or fifth tube in an EFIS, it replaces the weather radar screen and displays radar data, navigation maps, checklists and other information.

MVA - Minimum Vectoring Altitude.

MZFW - Maximum Zero-Fuel Weight.