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. 

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. 

Lubber line.  The reference line used in a magnetic compass or heading indicator. 

## M 

MAA.  See maximum authorized altitude. 

MAC. See mean aerodynamic chord. 

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. 

Mach meter. The instrument that displays the ratio of the speed of sound to the true airspeed an aircraft is flying. 

Magnetic bearing (MB).  The direction to or from a radio transmitting station measured relative to magnetic north. 

Magnetic compass. A device for determining direction measured from 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 heading (MH).  The direction an aircraft is pointed with respect to 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. 

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. 

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. 

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. 

