<Li> Aircraft conducting WAAS approaches must possess certified GPS receivers, which are much more expensive than non-certified units . In 2006, Garmin's least expensive certified receiver, the GNS 430W, had a suggested retail price of US $10,750 . </Li> <Li> WAAS is not capable of the accuracies required for Category II or III ILS approaches . Thus, WAAS is not a sole - solution and either existing ILS equipment must be maintained or it must be replaced by new systems, such as the Local Area Augmentation System (LAAS). </Li> <Li> WAAS Localizer Performance with Vertical guidance (LPV) approaches with 200 - foot minimums will not be published for airports without medium intensity lighting, precision runway markings and a parallel taxiway . Smaller airports, which currently may not have these features, would have to upgrade their facilities or require pilots to use higher minimums . </Li> <Li> As precision increases and error approaches zero, the navigation paradox states that there is an increased collision risk, as the likelihood of two craft occupying the same space on the shortest distance line between two navigational points has increased . </Li>

How many satellites do you need for waas