Flight management systems (FMS) and area navigation (RNAV) systems are an increasingly popular method of navigating that allows pilots to make more efficient use of the national airspace system. The increasing number of users is attributable to more economical and accurate satellite signal receivers and computer chips. RNAV systems may use VHF omnidirectional range (VOR); distance measuring equipment (DME) (VOR/DME, DME/DME) signals; inertial navigation systems (INS); Doppler radar; the current version of LOng RAnge Navigation (LORAN), LORAN-C (and eLORAN, as it becomes operational); and the global positioning system (GPS), to name a few. Ground-based LORAN-C is a reliable complement to spacebased GPS systems (United States Department of Defense (DOD) GPS, Russian Global Navigation Satellite System (GLONASS), and European Galileo in the future).
Wide area augmentation system (WAAS) of the standard GPS furnishes additional error correction information, allowing Category I precision approaches (similar to basic instrument landing system (ILS) minimums) to units equipped to receive and integrate the data. Most general aviation pilots learn to work with an FMS unit primarily using GPS signals, possibly with WAAS and LORAN-C options. Older RNAV units made use of VOR and DME information to compute positions within range of the navaids. Newer units contain databases that allow route programming with automatic sequencing through the selected navigation points. Therefore, flight management system (FMS) is the best descriptor of the current GPS units integrating VOR (and DME, optionally) to allow point-to-point navigation outside established flight routes. You will learn to use the FMS data entry controls to program a flight route, review the planned route, track and make modifications to the planned route while en route, plan and execute a descent, and fly an approach procedure that is based solely on RNAV signals. You should remember that FMS/RNAV units requiring external signals for navigation are usually restricted to line-of-sight reception (LORAN-C being somewhat of an exception). Therefore, navigation information in valleys and canyons that could block satellite signals may be severely restricted. Users in those areas should pay particular attention to the altitude or elevations of the satellites when depending on space-based signals and plan flight altitudes to ensure line-of-sight signal reception. Review the GPS unit’s documentation sufficiently to determine if WAAS is installed and how WAAS corrections are indicated.