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. 

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. 

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. 

Jointer. A woodworking power tool used to smooth edges of a piece of wood. 

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. 

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. 

Key (verb).  To initiate an action by depressing a key or a button. 

kHz (kilohertz).  1,000 cycles per second. 

Kick-in pressure.  The pressure at which an unloading valve causes a hydraulic pump to direct its fluid into the system manifold. 

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. 

Kilogram.  One thousand grams. 

Kinetic energy.  Energy that exists because of motion. 

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. 

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. 

