Military training route (MTR).  Airspace of defined vertical and lateral dimensions established for the conduct of military training at airspeeds in excess of 250 knots indicated airspeed (KIAS). 

Minimum altitude.  An altitude depicted on an instrument approach chart with the altitude value underscored. Aircraft are required to maintain altitude at or above the depicted value. 

Minimum crossing altitude (MCA).  The lowest allowed altitude at certain fixes an aircraft must cross when proceeding in the direction of a higher minimum en route altitude (MEA). 

Minimum descent altitude (MDA).  The lowest altitude (in feet MSL) to which descent is authorized on final approach, or during circle-to-land maneuvering in execution of a nonprecision approach. 

Minimum drag. The point on the total drag curve where the lift-to-drag ratio is the greatest. At this speed, total drag is minimized. 

Minimum en route altitude (MEA). The lowest published altitude between radio fixes that ensures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. 

Minimum equipment list (MEL). A list developed for larger aircraft that outlines equipment that can be inoperative for various types of flight including IFR and icing conditions. This list is based on the master minimum equipment list (MMEL) developed by the FAA and must be approved by the FAA for use. It is specific to an individual aircraft make and model. 

Minimum obstruction clearance altitude (MOCA).  The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments, which meets obstacle clearance requirements for the entire route segment and which ensures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR. 

Minimum reception altitude (MRA). The lowest altitude at which an airway intersection can be determined. 

Minimum safe altitude (MSA). The minimum altitude depicted on approach charts which provides at least 1,000 feet of obstacle clearance for emergency use within a specified distance from the listed navigation facility. 

Minimum vectoring altitude (MVA).  An IFR altitude lower than the minimum en route altitude (MEA) that provides terrain and obstacle clearance. 

Minimums section.  The area on an IAP chart that displays the lowest altitude and visibility requirements for the approach. 

Missed approach.  A maneuver conducted by a pilot when an instrument approach cannot be completed to a landing. 

Missed approach point (MAP). A point prescribed in each instrument approach at which a missed approach procedure shall be executed if the required visual reference has not been established. 

Mixed ice.  A mixture of clear ice and rime ice. 

MLS.  See microwave landing system. 

MM.  Middle marker. 

MOA.  See military operations area. 

MOCA.  See minimum obstruction clearance altitude. 

Mode C.  Altitude reporting transponder mode. 

Moment. The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG. 

Moment arm. The distance from a datum to the applied force. 

Moment index (or index). A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of airplanes where heavy items and long arms result in large, unmanageable numbers. 

Monocoque. A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers. 

Monoplanes. Airplanes with a single set of wings. 

Movable slat. A movable auxiliary airfoil on the leading edge of a wing. It is closed in normal flight but extends at high angles of attack. This allows air to continue flowing over the top of the wing and delays airflow separation. 

MRA.  See minimum reception altitude. 

MSA.  See minimum safe altitude. 

MSL.  See mean sea level. 

