IA (Inspection Authorization). An authorization issued by the Federal Aviation Administration to certain licensed and experienced aviation maintenance technicians that allows them to perform annual and progressive inspections. This authorization also allows them to approve aircraft for return to service after certain types of major repairs and major alterations.
IAF (initial approach fix) (air traffic control). The fixes depicted on the instrument approach procedure charts that identify the beginning of the initial approach segment(s).
IAP (instrument approach procedure). A series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.
IAS (indicated airspeed). The speed an aircraft is moving through the air as is shown on the air-speed indicator, before any corrections for errors or nonstandard conditions are made.
I-beam. A piece of structural material having a cross-sectional shape that resembles the letter “I.” I-beams used in aircraft structure may be extruded or built up from aluminum alloys, or they may be made of wood. Wooden I-beams may be either built up of several pieces of wood or shaped by removing some of the wood from the sides of the beam with a router.

IC (integrated circuit). A combination of electronic components built onto a single substrate of semiconductor material. Transistors, diodes, capacitors, and resistors are all built onto a tiny chip and mounted in a protective package that allows the circuit to connect with other components or devices.
Logic gates, rectifiers, amplifiers, microprocessors, and semiconductor memory circuits can all be built as integrated circuits. The development of integrated circuits has made miniature electronics possible.
ICAO (International Civil Aviation Organization). A specialized agency of the United Nations whose objective is to develop the principles and techniques of international air navigation and to foster planning and development of international civil air transport. The term ICAO is normally pronounced as a single word (eye-kay-o), rather than using the entire name or the initials.
icebox rivet (aircraft fastener). A solid aircraft rivet made of 2017 or 2024 aluminum alloy. These rivets are too hard to drive in the condition they are received from the manufacturer, and they must be heat-treated to soften them. They are heated in a furnace and then quenched in water. Immediately after quenching, they are soft, but within a few hours at room temperature, they become quite hard.
Hardening can be delayed for several days by immediately placing the rivets in a subfreezing icebox and holding them at this low temperature until they are used.
ice bridging. A spark plug failure that occurs when a reciprocating engine is started in extremely cold weather. When a cylinder fires, the fuel-air mixture is converted into carbon dioxide and water vapor. The water vapor condenses on the spark plug electrodes and forms ice that bridges the electrode gap and prevents the plug firing until the ice is melted. This normally requires removing the spark plugs from the engine.