The US Federal Aviation Administration plans new categories of approach guidance based on the expected performance of the wide area augmentation system (WAAS). Details revealed at the WAAS users' summit in mid-March suggest the new levels will provide increased operational benefit earlier than expected.

The FAA told users that an initial level of approach guidance, called lateral and vertical navigation (LNAV/VNAV), could be certificated by 2002. Now WAAS prime contractor Raytheon says a second level of capability, providing lower approach minima, could also become available in 2002.

The FAA plans three levels of approach guidance using WAAS, which increases the accuracy and integrity of global positioning system (GPS) signals:

• LNAV/VNAV will allow pilots to follow a "virtual glideslope" down to a 350ft (105m) decision height and 1.4-1.85km (0.75-1nm) runway visibility;

• GPS landing system (GLS) will allow approach to a decision height of 250-350ft and 1.4km visibility;

• GLS precision approach will be equivalent to Category I, with a 200ft decision height and 900m visibility at Cat 1 runways.

Source: Flight International