- IAS Indicated airspeed, airspeed indicator reading corrected for instrument error.
- IATA International Air Transport Association.
- ICAO International Civil Aviation Organisation.
- IFF Identification friend or foe.
- IFR (1) Instrument flights rules (compare VFR); (2) in-flight refuelling.
- IGE In ground effect: helicopter performance with theoretical flat horizontal surface just below it (for example mountain).
- IIR Imaging infra-red.
- ILS Instrument landing system. See Cat.
- Imperial gallon 1.20095 US gallons; 4.546 litres.
- INAS Integrated nav/attack system.
- Inc Incorporated (company constitution).
- incidence The angle at which the wing is set in relation to the fore/aft axis. Often wrongly used to mean angle of attack (which see).
- inertial navigation Measuring all accelerations imparted to vehicle and, by integrating these with respect to time, calculating speed at every instant (in all three planes) and, by integrating a second time, calculating total change of position in relation to starting point.
- INS Inertial navigation system.
- integral construction Machined from solid instead or assembled from separate parts.
- integral tank Fuel (or other liquid) tank formed by sealing part of structure.
- intercom Wired telephone system for communication within aircraft.
- inverter Electric or electronic device for inverting (reversing polarity of) alternate waves in AC power to produce DC.
- IOC Initial operational capability.
- IR Infra-red.
- IRCM Infra-red countermeasures.
- IRLS Infra-red linescan (builds TV-type picture showing cool and hot regions as contrasting shades).
- IRS Inertial reference system.
- IRST Infra-red search and track.
- ISA International Standard Atmosphere (1013.25 mb, 1,225 g/m³ and 15°C at mean sea level; lapse rate 1.98°C per 1,000 ft up to -56,5°C at 36,090 ft).
