izer ▁must ▁shut ▁down ▁in ▁less ▁than ▁ 2 ▁seconds . ▁ ▁Special ▁C AT ▁II ▁and ▁C AT ▁III ▁operations ▁ ▁In ▁contrast ▁to ▁other ▁operations , ▁C AT ▁III ▁weather ▁min ima ▁do ▁not ▁provide ▁sufficient ▁visual ▁references ▁to ▁allow ▁a ▁manual ▁landing ▁to ▁be ▁made . ▁ ▁C AT ▁III b ▁min ima ▁depend ▁on ▁roll - out ▁control ▁and ▁redund ancy ▁of ▁the ▁aut op il ot , ▁because ▁they ▁give ▁only ▁enough ▁time ▁for ▁the ▁pilot ▁to ▁decide ▁whether ▁the ▁aircraft ▁will ▁land ▁in ▁the ▁touch down ▁zone ▁( bas ically ▁C AT ▁III a ) ▁and ▁to ▁ensure ▁safety ▁during ▁roll out ▁( bas ically ▁C AT ▁III b ). ▁Therefore , ▁an ▁automatic ▁landing ▁system ▁is ▁mand atory ▁to ▁perform ▁Category ▁III ▁operations . ▁Its ▁reli ability ▁must ▁be ▁sufficient ▁to ▁control ▁the ▁aircraft ▁to ▁touch down ▁in ▁C AT ▁III a ▁operations ▁and ▁through ▁roll out ▁to ▁a ▁safe ▁tax i ▁speed ▁in ▁C AT ▁III b ▁( and ▁C AT ▁III c ▁when ▁author ized ). ▁However , ▁special ▁appro val ▁has ▁been ▁granted ▁to ▁some ▁operators ▁for ▁hand - flow n ▁C AT ▁III ▁approaches ▁using ▁a ▁head - up ▁display ▁( H UD ) ▁guidance ▁that ▁provides ▁the ▁pilot ▁with ▁an ▁image ▁viewed ▁through ▁the ▁wind sh ield ▁with ▁eyes ▁focused ▁at ▁infinity , ▁of ▁necessary ▁electronic ▁guidance ▁to ▁land ▁the ▁air plane ▁with ▁no ▁true ▁outside ▁visual ▁references . ▁ ▁In ▁the ▁United ▁States , ▁air ports ▁with ▁C AT ▁III