Magnetic compass.  A device for determining direction  measured from magnetic north. Magneto.  A self-contained engine-driven unit that supplies  electrical current to the spark plugs  completely independent  of the airplane’s electrical system. Normally there are two  magnetos per engine. Make/model.  Refers to the manufacturer and model of a  specific aircraft. Maneuvering altitude.  An altitude above the ground  that allows a sufficient margin of height to permit safe  maneuvering. Maneuvering speed (V$_{A}$).  The maximum speed at which full   abrupt control movement can be used without overstressing  the airframe. Maneuverability.  Ability of an aircraft to change directions  along a flightpath and withstand the stresses imposed upon  it. Mast.  The carriage structural component that is attached to  the rear of the carriage keel and the top of the front tube. The  top is the carriage attachment the wing.  Maximum gross weight.  The maximum authorized weight  of the aircraft and all of its equipment as specified in the  POH/AFM/AOI for the aircraft. Maximum structure cruising speed (V$_{NO}$).  The speed not  to exceed except in smooth air; the upper limit of the green  arc. Mean aerodynamic chord (MAC).  The average distance  from the leading edge to the trailing edge of the wing. Mean sea level (MSL).  The average height of the surface  of the sea for all stages of tide. A number preceding MSL  indicates altitude in feet above mean sea level. Mechanical Turbulence.  Type of turbulence caused by  obstructions on the ground interfering with smooth flow  of the wind. Trees  buildings and terrain can all cause  mechanical turbulence. Medical certificate.  Acceptable evidence of physical fitness  on a form prescribed by the Administrator. Medium-banked turn.  Turn resulting from a degree of bank  (approximately 20 to 45 degrees) at which the WSC remains  at a constant bank. METAR.  See Aviation Routine Weather Report. Microburts.  A strong downdraft which normally occurs over  horizontal distances of 1 NM or less and vertical distances of  less than 1 000 feet. In spite of its small horizontal scale  an  intense microburst could induce windspeeds greater than 100  knots and downdrafts as strong as 6 000 feet per minute. Military Operations Area (MOA).  Airspace of defined  vertical and lateral limits established for the purpose of  separating certain military training activity from IFR  traffic. Military Training Routes (MTR).  Special routes developed  to allow the military to conduct low-altitude  high-speed  training. Minimum controllable airspeed.  An airspeed at which any  further increase in angle of attack  increase in load factor  or  reduction in power  would result in an immediate stall. Minimum drag speed (L/D$_{MAX}$).  The point on the total  drag curve where the lift-to-drag ratio is the greatest. At this  speed  total drag is minimized. Mindset.  A factor in aeronautical decision making where  decision making is influenced by preconceived ideas about  the outcome of events. For example  an expectation of  improving weather conditions can lead to increased risk  during a flight. Mixture.  The ratio of fuel to air entering the engine’s  cylinders. MOA.  See Military operations Area. Mode C transponder.  A receiver/transmitter which will  generate a radar reply signal upon proper interrogation; the  interrogation and reply being on different frequencies. Mode  C means the reply signal includes altitude information. Moment. A force that causes or tries to cause an object to  rotate. 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 PPC multiplied by the distance  between the datum and the CG. Moment arm.  The distance from a datum to the applied  force. MSL.  See mean sea level. G-11