: M oll us cs ▁of ▁the ▁United ▁States ▁m cm ich ael i ▁Category : M oll us cs ▁described ▁in ▁ 1 9 5 6 ▁Category : T ax onomy ▁articles ▁created ▁by ▁Pol bot <0x0A> </s> ▁R ED I RECT ▁P ine al ▁g land <0x0A> </s> ▁An ▁instrument ▁landing ▁system ▁( IL S ) ▁is ▁a ▁system ▁that ▁works ▁by ▁sending ▁radio ▁waves ▁down range ▁from ▁the ▁run way ▁end , ▁with ▁aircraft ▁that ▁intercept ▁it ▁using ▁the ▁radio ▁waves ▁to ▁guide ▁them ▁onto ▁the ▁run way . ▁It ▁is ▁defined ▁by ▁the ▁International ▁Tele communic ation ▁Union ▁as ▁a ▁service ▁provided ▁by ▁a ▁station ▁as ▁follows : ▁ ▁Princi ple ▁of ▁operation ▁▁ ▁An ▁instrument ▁landing ▁system ▁oper ates ▁as ▁a ▁ground - based ▁instrument ▁approach ▁system ▁that ▁provides ▁precision ▁later al ▁and ▁vertical ▁guidance ▁to ▁an ▁aircraft ▁approaching ▁and ▁landing ▁on ▁a ▁run way , ▁using ▁a ▁combination ▁of ▁radio ▁signals ▁and , ▁in ▁many ▁cases , ▁high - int ens ity ▁light ing ▁arrays ▁to ▁enable ▁a ▁safe ▁landing ▁during ▁instrument ▁meteor ological ▁conditions ▁( IM C ), ▁such ▁as ▁low ▁ce il ings ▁or ▁reduced ▁visibility ▁due ▁to ▁fog , ▁rain , ▁or ▁blow ing ▁snow . ▁ ▁An ▁instrument ▁approach ▁procedure ▁chart ▁( or ▁' appro ach ▁plate ') ▁is ▁published ▁for ▁each ▁I LS ▁approach ▁to ▁provide ▁the ▁information ▁needed ▁to ▁fly ▁an ▁I LS ▁approach ▁during ▁instrument ▁flight ▁rules ▁( IF R ) ▁operations . ▁A ▁chart ▁includes ▁the ▁radio ▁frequencies ▁used