RNAV (GPS) approaches to LPV lines of minima take advantage of the improved accuracy of WAAS lateral and vertical guidance to provide an approach that is very similar to a Category I (CAT I) ILS. Localizer Performance with Vertical Guidance (LPV)Īn RNAV function requiring WAAS, using a final approach segment (FAS) data block, which computes, displays and provides both horizontal and approved vertical approach navigation to minimums as low as 200 foot ceiling and ½ mile visibility. In an approach with approved vertical guidance, DA is a specified altitude expressed in feet above mean sea level (MSL) at which a missed approach must be initiated if the required visual references to continue the approach have not been established. Standard for Terminal Instrument Procedures (TERPS)-protected glide path (e.g., approaches with LNAV/VNAV, LPV or ILS lines of minima).
The user receives GPS constellation augmentation information from a geostationary satellite-based transmitter.
SBAS is a wide area coverage augmentation system.Satellite-Based Augmentation System (SBAS) When a pilot selects an approach procedure, WAAS avionics display the best level of service supported by the combination of the WAAS signal-in-space, the aircraft avionics, and the selected RNAV (GPS) instrument approach. However, like most other navigation services, the WAAS network has service volume limits, and some airports on the fringe of WAAS coverage may experience reduced availability of WAAS vertical guidance. Temperature and pressure extremes do not affect WAAS vertical guidance unlike when baro-VNAV is used to fly to LNAV/VNAV line of minima. One of the major improvements WAAS provides is the ability to generate glide path guidance independent of ground equipment. WAAS avionics with an appropriate airworthiness approval can enable aircraft to fly to the LPV, LP, LNAV/VNAV and LNAV lines of minima on RNAV (GPS) approaches.
If there are no airworthiness limitations on other installed navigation equipment, WAAS avionics enable aircraft navigation during all phases of flight from takeoff through vertically guided approaches and guided missed approaches. Additionally, the WAAS geostationary satellites provide ranging sources to supplement the GPS signals. WAAS improves the accuracy, integrity, availability and continuity of GPS signals.