international standard atmos-phere /.nt.n.(.)n.l stnd.d
tm.sf../ noun an internationally agreed unit of pressure used in the cali-bration of instruments and the measure-ment of aircraft performance . For en route weather the datum chosen is international standard atmosphere at mean sea level. Abbreviation ISA
interphone /.nt.f.υn/ an internal telephone communications system within an aircraft that enables members of the crew to speak to one another
interpolation /.ntp.le..(.)n/
noun the estimation of a middle value by reference to known values each side
. Spot temperatures at positions other than those printed are obtained by interpolation.
interpret /.ntpr.t/ verb to under-stand something presented in code or symbolic form . Aircrew must be able to interpret information printed on a contour chart.
interpretation /.ntpr.te..(.)n/
noun an understanding of something presented in code or symbolic form .
Synoptic charts require interpretation in order to understand the information given.
interrogate /.nter.e.t/ verb to
transmit SSR or ATC signals to activate a transponder . Secondary surveillance radar interrogates the aircraft equip-ment which responds with identification and height information.
interrogation /.nter.e..(.)n/
noun the transmission of a SSR or ATC signal to activate a transponder . A transponder replies to interrogation by passing a four-digit code.
interrogator /.nter.e.t./ noun a
ground-based surveillance radar beacon transmitter/receiver . The questioner, better known as the interrogator, is fit-ted on the ground, while the responder, also known as the transponder, is an airborne installation.
interrupt /.nt.rpt/ verb to break the continuity of something . The con-versation was interrupted by a tele-phone call. . In the northern hemi-sphere, the westerly flow of air is

interruption 126
interrupted by variations which occur in pressure patterns.
interruption /.nt.rp..n/ noun a
break in the continuity of something .
Because of the summer holiday, there was an interruption in the flying train-ing course.
intersect /.nt.sekt/ verb to cut across each other . Meridians intersect at the poles and cross the equator at right angles.
intersection /.nt.sek..n/ noun the
point at which two lines cross each other . The aircraft came to a stop at the intersection between runways 09 and 16. . The intersection of the drift line and the wind vector gives the drift point.

intertropical convergence zone
/.nt.tr.p.k(.)l k.nvd.ns z.υn/ noun the boundary between the trade winds and tropical air masses from the northern and southern hemispheres .
The intertropical convergence zone is the zone in which the trade winds from the two hemispheres approach each other. Abbreviation ITCZ
interval /.nt.v(.)l/ noun 1. the amount of space between places or points . The intervals at which contours are drawn depends on the scale of the chart and this interval, known as the vertical interval, is noted on the chart.