▁is ▁expected ▁to ▁play ▁a ▁key ▁role ▁in ▁modern ization ▁and ▁in ▁all - we ather ▁operations ▁cap ability ▁at ▁C AT I / II ▁and ▁III ▁air ports , ▁terminal ▁area ▁navigation , ▁missed ▁approach ▁guidance ▁and ▁surface ▁operations . ▁GB AS ▁provides ▁the ▁cap ability ▁to ▁service ▁the ▁entire ▁air port ▁with ▁a ▁single ▁frequency ▁( V H F ▁transmission ) ▁whereas ▁I LS ▁requires ▁a ▁separate ▁frequency ▁for ▁each ▁run way ▁end . ▁GB AS ▁C AT - I ▁is ▁seen ▁as ▁a ▁necessary ▁step ▁towards ▁the ▁more ▁string ent ▁operations ▁of ▁C AT - II / III ▁precision ▁approach ▁and ▁landing . ▁The ▁technical ▁risk ▁of ▁implementing ▁GB AS ▁delayed ▁w ides p read ▁accept ance ▁of ▁the ▁technology . ▁The ▁F AA , ▁along ▁with ▁industry , ▁have ▁field ed ▁Prov ably ▁Sa fe ▁Pro totype ▁GB AS ▁stations ▁that ▁mit ig ate ▁the ▁impact ▁of ▁satellite ▁signal ▁de formation , ▁ion os phere ▁differential ▁error , ▁e ph emer is ▁error , ▁and ▁multip ath . ▁ ▁Future ▁The ▁advent ▁of ▁the ▁Global ▁Position ing ▁System ▁( G PS ) ▁provides ▁an ▁alternative ▁source ▁of ▁approach ▁guidance ▁for ▁aircraft . ▁In ▁the ▁US , ▁the ▁W ide ▁Area ▁Aug ment ation ▁System ▁( WA AS ) ▁has ▁been ▁available ▁in ▁many ▁regions ▁to ▁provide ▁precision ▁guidance ▁to ▁Category ▁I ▁standards ▁since ▁ 2 0 0 7 . ▁The ▁equivalent ▁European ▁Ge ost ation ary ▁Navigation ▁Over lay ▁Service ▁( EG N OS ) ▁was ▁cert ified ▁for