Kollsman window.  The barometric scale window of a sensitive altimeter. See barometric scale. 

Koroseal lacing.  A plastic lacing material available in round or rectangular cross sections and used for holding wire bundles and tubing together. It holds tension on knots indefinitely and is impervious to petroleum products. 

Kraft paper.  A tough brown wrapping paper, like that used for paper bags. 

Lacquer.  A finishing material made of a film base, solvents, plasticizers, and thinners. The film base forms a tough film over the surface when it dries. The solvents dissolve the film base so it can be applied as a liquid. The plasticizers give the film base the needed resilience, and the thinners dilute the lacquer so it can be applied with a spray gun. Lacquer is sprayed on the surface as a liquid, and when the solvents and thinners evaporate, the film base remains as a tough decorative and protective coating. 

Landing gear warning system.  A system of lights used to indicate the condition of the landing gear. A red light illuminates when any of the gears are in an unsafe condition; a green light shows when all of the gears are down and locked, and no light is lit when the gears are all up and locked. An aural warning system is installed that sounds a horn if any of the landing gears are not down and locked when the throttles are retarded for landing. 

Laminar flow.  Airflow in which the air passes over the surface in smooth layers with a minimum of turbulence. 

Laminated wood.  A type of wood made by gluing several pieces of thin wood together. The grain of all pieces runs in the same direction. 

Latent heat.  Heat that is added to a material that causes a change in its state without changing its temperature. 

Lateral axis.  An imaginary line, passing through the center of gravity of an airplane, and extending across it from wing tip to wing tip. 

Lay-up.  The placement of the various layers of resin- impregnated fabric in the mold for a piece of laminated composite material. 

L/D ratio.  A measure of efficiency of an airfoil. It is the ratio of the lift to the total drag at a specified angle of attack. 

Left-right indicator.  The course-deviation indicator used with a VOR navigation system. 

Lightning hole. A hole cut in a piece of structural material to get rid of weight without losing any strength. A hole several inches in diameter may be cut in a piece of metal at a point where the metal is not needed for strength, and the edges of the hole are flanged to give it rigidity. A piece of metal with properly flanged lightning holes is more rigid than the metal before the holes were cut. 

Linear actuator.  A fluid power actuator that uses a piston moving inside a cylinder to change pressure into linear, or straight-line, motion. 

Linear change.  A change in which the output is directly proportional to the input. 

Loadmeter.  A current meter used in some aircraft electrical systems to show the amount of current the generator or alternator is producing. Loadmeters are calibrated in percent of the generator rated output. 

Localizer. The portion of an ILS (Instrument Landing System) that directs the pilot along the center line of the instrument runway. 

Lodestone. A magnetized piece of natural iron oxide. 

Logic flow chart. A type of graphic chart that can be made up for a specific process or procedure to help follow the process through all of its logical steps. 

Longitudinal axis.  An imaginary line, passing through the center of gravity of an airplane, and extending lengthwise through it from nose to tail. 

Longitudinal stability.  Stability of an aircraft along its longitudinal axis and about its lateral axis. Longitudinal stability is also called pitch stability. 

LORAN A. Long Range Aid to Navigation. A hyperbolic navigation system that operates with frequencies of 1,950 kHz, 1,850 kHz, and 1,900 kHz. 

LORAN C.  The LORAN system used in aircraft. It operates on a frequency of 100 kHz. 

LRU.  Line replaceable unit. 

Lubber line. A reference on a magnetic compass and directional gyro that represents the nose of the aircraft. The heading of the aircraft is shown on the compass card opposite the lubber line. 

