Garmin's GPS-400W offers the least expensive entry into WAAS GPS operation. While the GPS-400W lacks the VOR/LOC/Glideslope Receiver and COMM Transceiver of the more expensive GNS-430W, the GPS-400W offers the same capability as an IFR WAAS GPS Navigator and a Multi-Function Display (MFD). WAAS Approach Capability - WAAS, or Wide Area Augmentation System, is a fundamental improvement to GPS accuracy. By adding a series of ground stations and geostationary satellites, WAAS GPS is typically 5 times more accurate than "regular" GPS. This means that it is now possible to fly a complete "Virtual Glideslope" approach into an airport with no local ground-based navigation aids whatsoever. A GPS-400W makes the following approaches available:
- LNAV (Lateral Navigation): This is a new name for non-precision GPS approaches as we have known them. Like all non-precision approaches, this has a minimum descent altitude (MDA), based on obstructions and terrain.
- LNAV/VNAV (Lateral Navigation / Vertical Navigation): This class of approach provides Glideslope vertical guidance with a decision altitude (DA) typically 350 feet AGL.
- LPV (Localizer Performance with Vertical guidance): This is the most precise of the WAAS GPS approaches, the GPS equivalent of a Cat I ILS approach. It also offers Glideslope vertical guidance, but the DA is lower, typically from 200-250 feet AGL.
There are thousands of FAA-approved LPV WAAS approaches, with more being added regularly. The FAA's stated goal is to have a WAAS approach available for every public runway at least 3,200 feet long. To see if the airports you use offer WAAS capability, please click here for the FAA's information about GPS/WAAS Approaches. Terrain Information - With the GPS-400W, the terrain database is standard (for improved awareness and safety), and it provides this information with greater resolution and precision than the original GPS-400. Other GPS-400W features include:
- Faster position calculations and screen updates (5x per second)
- Improved annunciation
- Holding patterns
- Autopilot roll steering
- Parallel track calculation
- Dead reckoning (This is a backup if GPS signal is lost)
- More informative status pages
- Configuration for GDL-69 / GDL-69A XM Receivers (if installed)
- Simplified installation paperwork