Load factor.  The ratio of a specified load to the total weight  of the aircraft. The specified load is expressed in terms of  any of the following: aerodynamic forces, inertial forces, or  ground or water reactions.  Loadmeter.  A type of ammeter installed between the generator  output and the main bus in an aircraft electrical system.  LOC.  See localizer.  Local area augmentation system (LAAS).  A differential  global positioning system (DGPS) that improves the accuracy  of the system by determining position error from the GPS  satellites, then transmitting the error, or corrective factors,  to the airborne GPS receiver.  Localizer (LOC).  The portion of an ILS that gives left/right  guidance information down the centerline of the instrument  runway for final approach.  Localizer-type directional aid (LDA).  A NAVAID used  for nonprecision instrument approaches with utility and  accuracy comparable to a localizer but which is not a part  of a complete ILS and is not aligned with the runway. Some  LDAs are equipped with a glideslope.  Locator middle marker (LMM).  Nondirectional radio  beacon (NDB) compass locator, collocated with a middle  marker (MM).  Locator outer marker (LOM).  NDB compass locator,  collocated with an outer marker (OM).  LOM.  See locator outer marker.  Longitude.  Measurement east or west of the Prime Meridian  in degrees, minutes, and seconds. The Prime Meridian is 0°  longitude and runs through Greenwich, England. Lines of  longitude are also referred to as meridians.  Longitudinal axis.  An imaginary line through an aircraft  from nose to tail, passing through its center of gravity. The  longitudinal axis is also called the roll axis of the aircraft.  Movement of the ailerons rotates an airplane about its  longitudinal axis.  Longitudinal stability (pitching).  Stability about the lateral  axis. A desirable characteristic of an airplane whereby it tends  to return to its trimmed angle of attack after displacement.  Mandatory block altitude.  An altitude depicted on an  instrument approach chart with two underscored and  overscored altitude values between which aircraft are  required to maintain altitude.  Mandatory altitude.  An altitude depicted on an instrument  approach chart with the altitude value both underscored and  overscored. Aircraft are required to maintain altitude at the  depicted value.  Magnus effect.  Lifting force produced when a rotating  cylinder produces a pressure differential. This is the same  effect that makes a baseball curve or a golf ball slice.  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.  Magnetic heading (MH).  The direction an aircraft is pointed  with respect to magnetic north.  Magnetic dip.  A vertical attraction between a compass  needle and the magnetic poles. The closer the aircraft is to a  pole, the more severe the effect.  Magnetic compass.  A device for determining direction  measured from magnetic north.  Magnetic bearing (MB).  The direction to or from a radio  transmitting station measured relative to magnetic north.  Mach meter.  The instrument that displays the ratio of the  speed of sound to the true airspeed an aircraft is flying.  Mach number.  The ratio of the true airspeed of the aircraft  to the speed of sound in the same atmospheric conditions,  named in honor of Ernst Mach, late 19th century physicist.  MAA.  See maximum authorized altitude.  MAC.  See mean aerodynamic chord.  Lubber line.  The reference line used in a magnetic compass  or heading indicator.  Low or medium frequency.  A frequency range between  190 and 535 kHz with the medium frequency above 300  kHz. Generally associated with nondirectional beacons  transmitting a continuous carrier with either a 400 or 1,020  Hz modulation.  M  G-18 