Infrared radiation.  Electromagnetic radiation whose  wavelengths are longer than those of visible light. Ingot.  A large block of metal that was molded as it was  poured from the furnace. Ingots are further processed into  sheets, bars, tubes, or structural beams. INS.  Inertial Navigation System. Inspection Authorization (IA).  An authorization that may  be issued to an experienced aviation maintenance technician  who holds both an Airframe and Powerplant rating. It allows  the holder to conduct annual inspections and to approve an  aircraft or aircraft engine for return to service after a major  repair or major alteration. Integral fuel tank.  A fuel tank which is formed by sealing  off part of the aircraft structure and using it as a fuel tank.  An integral wing tank is called a “wet wing.” Integral tanks  are used because of their large weight saving. The only way  of repairing an integral fuel tank is by replacing damaged  sealant and making riveted repairs, as is done with any other  part of the aircraft structure. Interference drag.  Parasite drag caused by air flowing over  one portion of the airframe interfering with the smooth flow  of air over another portion. Intermittent-duty solenoid.  A solenoid-type switch whose  coil is designed for current to flow through it for only a  short period of time. The coil will overheat if current flows  through it too long. IRS.  Inertial Reference System. IRU.  Inertial Reference Unit. Iso-octane.  A hydrocarbon, C$_{8}$H$_{18}$, which has very high  critical pressure and temperature. Iso-octane is used  as the high reference for measuring the antidetonation  characteristics of a fuel. Isobaric mode.  The mode of pressurization in which the  cabin pressure is maintained at a constant value regardless  of the outside air pressure. Isogonic line.  A line drawn on an aeronautical chart along  which the angular difference between the magnetic and  geographic north poles is the same. Isopropyl alcohol.  A colorless liquid used in the manufacture  of acetone and its derivatives and as a solvent and anti-icing  agent. Knot (measure of speed).  A speed measurement that is  equal to one nautical mile per hour. One knot is equal to 1.15  statute mile per hour. Knot (wood defect).  A hard, usually round section of a  tree branch embedded in a board. The grain of the knot is  perpendicular to the grain of the board. Knots decrease the  strength of the board and should be avoided where strength  is needed. Kinetic energy.  Energy that exists because of motion. Kilogram.  One thousand grams. Kick-out pressure.  The pressure at which an unloading  valve shuts off the flow of fluid into the system pressure  manifold and directs it back to the reservoir under a much  reduced pressure. Kick-in pressure.  The pressure at which an unloading valve  causes a hydraulic pump to direct its fluid into the system  manifold. kHz (kilohertz).  1,000 cycles per second. Key (verb).  To initiate an action by depressing a key or a button. Kevlar.  A patented synthetic aramid fiber noted for its  flexibility and light weight. It is to a great extent replacing  fiberglass as a reinforcing fabric for composite construction. K-factor.  A factor used in sheet metal work to determine the  setback for other than a 90° bend. Setback = K ∙ (bend radius  + metal thickness). For bends of less than 90°, the value of  K is less than 1; for bends greater than 90°, the value of K  is greater than 1. Jointer.  A woodworking power tool used to smooth edges  of a piece of wood. Jet pump.  A special venturi in a line carrying air from certain  areas in an aircraft that need an augmented flow of air through  them. High-velocity compressor bleed air is blown into the  throat of a venturi where it produces a low pressure that pulls  air from the area to which it is connected. Jet pumps are often  used in the lines that pull air through galleys and toilet areas. Joggle.  A small offset near the edge of a piece of sheet metal.  It allows one sheet of metal to overlap another sheet while  maintaining a flush surface. Jackscrew.  A hardened steel rod with strong threads cut into  it. A jackscrew is rotated by hand or with a motor to apply  a force or to lift an object.  G-20