AERONAUTICAL GLOSSARY : ILS (INSTRUMENT LANDING SYSTEM) - JETSTREAM

ILS (INSTRUMENT LANDING SYSTEM) A precision instrument approach system, which normally consists of the following electronic components and visual aids—localizer, glide slope, outer marker, and approach lights.

INCLINOMETER—An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.

INDICATED AIRSPEED (IAS)— The direct instrument reading obtained from the airspeed indicator, uncorrected for variations in atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining airplane performance. Takeoff, landing, and stall speeds listed in the AFM or POH are indicated airspeeds and do not normally vary with altitude or temperature.

INDICATED ALTITUDE — The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.

INDUCED DRAG—That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed.

INTERCOOLER—A device used to reduce the temperatures of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.

INTERPOLATION—The estimation of an intermediate value of a quantity that falls between marked values in a series. Example: In a measurement of length, with a rule that is marked in 1/8's of an inch, the value falls between 3/8 inch and 1/2 inch. The estimated (interpolated) value might then be said to be 7/16 inch.

INVERSION—An increase in temperature with altitude.

ISA (INTERNATIONAL STANDARD ATMOSPHERE)—Standard atmospheric conditions consisting of a temperature of 59F (15C), and a barometric pressure of 29.92 in. Hg. (1013.2 mb) at sea level. ISA values can be calculated for various altitudes using a standard lapse rate of approximately 2ºC per 1,000 feet.

ISOBARS—Lines which connect points of equal barometric pressure.

ISOGONIC LINES—Lines on charts that connect points of equal magnetic variation.

JETSTREAM—A narrow band of wind with speeds of 100 to 200 m.p.h. usually co-located with the tropopause.