0 0 0 ▁feet ) ▁if ▁the ▁required ▁obst acle ▁clear ance ▁surfaces ▁are ▁clear ▁of ▁ob stru ctions . ▁Vis ibility ▁minim ums ▁of ▁ 1 / 2 ▁mile ▁( run way ▁visual ▁range ▁of ▁ 2 , 4 0 0 ▁feet ) ▁are ▁possible ▁with ▁a ▁C AT ▁I ▁I LS ▁approach ▁supported ▁by ▁a ▁ ▁A LS , ▁and ▁ 3 / 8 ▁mile ▁visibility ▁ ▁visual ▁range ▁is ▁possible ▁if ▁the ▁run way ▁has ▁high - int ens ity ▁edge ▁lights , ▁touch down ▁zone ▁and ▁center line ▁lights , ▁and ▁an ▁A LS ▁that ▁is ▁at ▁least ▁ ▁long ▁( see ▁Table ▁ 3 - 3 - 1 ▁" Min imum ▁visibility ▁values " ▁in ▁F AA ▁Order ▁ 8 2 6 0 . 3 C ). ▁In ▁effect , ▁A LS ▁extends ▁the ▁run way ▁environment ▁out ▁towards ▁the ▁landing ▁aircraft ▁and ▁allows ▁low - visibility ▁operations . ▁C AT ▁II ▁and ▁III ▁I LS ▁approaches ▁generally ▁require ▁complex ▁high - int ens ity ▁approach ▁light ▁systems , ▁while ▁medium - int ens ity ▁systems ▁are ▁usually ▁pa ired ▁with ▁C AT ▁I ▁I LS ▁approaches . ▁At ▁many ▁non - t ower ed ▁air ports , ▁the ▁pilot ▁controls ▁the ▁light ing ▁system ; ▁for ▁example , ▁the ▁pilot ▁can ▁key ▁the ▁micro phone ▁ 7 ▁times ▁to ▁turn ▁on ▁the ▁lights ▁on ▁the ▁high ▁intensity , ▁ 5 ▁times ▁to ▁medium ▁intensity ▁or ▁ 3 ▁times ▁for ▁low ▁intensity ▁ ▁Dec ision ▁alt itude /