Aeronautical Terms beginning with M
M
Mach Number.
MAA
Maximum Authorized IFR Altitude.
Mach number
The ratio of true airspeed to the speed of sound.
Main rotor
The rotor that supplies the principal lift to a rotorcraft.
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, powerplant 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
A repair:
(1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant 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.
MALS
Medium Intensity Approach Light System.
MALSR
Medium Intensity Approach Light System with Runway Alignment Indicator Lights.
Manifold pressure
Absolute pressure as measured at the appropriate point in the induction system and usually expressed in inches of mercury.
Maximum engine overtorque
As it applies to turbopropeller and turboshaft engines incorporating free power turbines for all ratings except one engine inoperative (OEI) ratings of two minutes or less, the maximum torque of the free power turbine rotor assembly, the inadvertent occurrence of which, for periods of up to 20 seconds, will not require rejection of the engine from service, or any maintenance action other than to correct the cause. Maximum speed for stability characteristics, V FC/MFC means a speed that may not be less than a speed midway between maximum operating limit speed (VMO/MMO) and demonstrated flight diving speed (VDF/MDF), except that, for altitudes where the Mach number is the limiting factor, MFC need not exceed the Mach number at which effective speed warning occurs.
MCA
Minimum Crossing Altitude.
MDA
Minimum Descent Altitude.
MEA
Minimum En Route Ifr Altitude.
Medical certificate
Acceptable evidence of physical fitness on a form prescribed by the Administrator.
MEL
Minimum Equipment List.
Military operations area
A military operations area (MOA) is airspace established outside Class A airspace to separate or segregate certain nonhazardous military activities from IFR Traffic and to identify for VFR traffic where theses activities are conducted.
Minimum descent altitude (MDA)
The lowest altitude specified in a [nonprecision] 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.
MM
ILS Middle Marker.
MOCA
Minimum Obstruction Clearance Altitude.
MRA
Minimum Reception Altitude.
MSL
Mean Sea Level.
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