Performance-Based Navigation

The NextGen system is based on the concept known as Performance-Based Navigation (PBN). PBN is basically a system of aircraft movement that maximizes on board navigation capabilities and options while reducing ground-based control personnel and Navaids. PBN is based on two fundamental elements: Area Navigation (RNAV) and Required Navigation Performance (RNP).

RNAV as a general concept has been around for a long time. It was first implemented by using the Navaid system of VORs and other ground-based facilities now in place. Avion­ics onboard aircraft could “move” Navaids to any point in two-dimensional space, thus cre­ating “waypoints” which could be used to fly direct routes. It was also subsequently used with LORAN airborne receivers in a similar man­ner for direct route navigation. The new RNAV system proposed in PBN uses satellite-based navigation and is much more sophisticated than previous concepts of RNAV.

Required Navigation Performance is a set of standards or parameters by which depar­ture, en route, approach, and landing must be accomplished by aircraft in the National Air­space System, and which requires the aircraft and its equipment to meet those associated per­formance standards. RNP contemplates a “trajec­tory” profile that will maximize the performance characteristics of jet aircraft and allow immediate climb to altitude and delayed, continuous descent to landing instead of the “stair-step” procedures currently in use for both climb and descent.

ADS-B Out

RNP requires the use of a new technology called Automatic Dependent Surveillance-Broadcast (ADS-B). ADS-B is a replacement for tra­ditional radar-based surveillance of aircraft. Instead of using ground-based radar to inter­rogate aircraft and determine their positions, each aircraft will use Global Navigation Satel­lite System (GNSS) technology (GPS in the U. S.; Galileo in Europe) to find its own position and then automatically report it to ground sta­tions (FAA stations in the United States) and to other aircraft equipped to receive it. At the same time, it reports the aircraft’s speed, heading, alti­tude, and flight number. This function is called ADS-B Out.

The FAA has mandated that all aircraft must have the ADS-B Out equipment installed by 2020. It is surmised that this equipment capabil­ity will be needed in areas where transponders are now required.

ADS-B In

The function of an aircraft receiving the reported position of other aircraft is called ADS-B In. There is no requirement yet for the installation of ADS-B In capability, primarily because there has been no consensus that this technology has proven its value relative to its cost.