Application of Area Navigation

RNAV airways provide more direct routings than the current VOR-based airway system, giving pilots easier access through terminal areas, while avoiding the circuitous routings now common in many busy Class B areas. RNAV airways are a critical component to the transition from ground-based navigation systems to GPS navigation. RNAV routes help maintain the aircraft flow through busy terminals by segregating arrival or departure traffic away from possibly interfering traffic flows.
Further, RNAV provides the potential for increasing airspace capacity both en route and in the terminal area in several important ways.
Strategic use of RNAV airways nationwide is reducing the cost of flying and providing aircraft owners more benefits from their IFR-certified GPS receivers. Several scenarios have been identified where RNAV routes provide a substantial benefit to users.

• Controllers are assigning routes that do not require overflying ground-based NAVAIDs such as VORs.
• The lateral separation between aircraft tracks is being reduced.
• RNAV routes lower altitude minimums on existing Victor airways where ground-based NAVAID performance (minimum reception altitude) required higher minimums.
• RNAV routes may allow continued use of existing airways where the ground-based NAVAID has been decommissioned or where the signal is no longer suitable for en route navigation.
• The route structure can be modified quickly and easily to meet the changing requirements of the user community.
• Shorter, simpler routes can be designed to minimize environmental impact. Dozens of new RNAV routes have been designated, and new ones are being added continuously. In order to designate RNAV airways, the FAA developed criteria, en route procedures, procedures for airway flight checks, and created new charting specifications. Some of the considerations include:
  
• Navigation infrastructure (i.e., the ground-based and space-based navigation positioning systems) provides adequate coverage for the proposed route/procedure.
• Navigation coordinate data meets International Civil Aviation Organization (ICAO) accuracy and integrity requirements. This means that all of the coordinates published in the Aeronautical Information Publication (AIP) and used in the aircraft navigation databases must be referenced to WGS 84, and the user must have the necessary assurance that this data has not been corrupted or inadvertently modified.
• Airborne systems meet airworthiness performance for use on the RNAV routes and procedures.
• Flight crews have the necessary approval to operate on the RNAV routes and procedures.

In the future, as aircraft achieve higher levels of navigation accuracy and integrity, closely spaced parallel routes may be introduced, effectively multiplying the number of available routes between terminal areas. RNAV can be used in all phases of flight and, when implemented correctly, results in:

• Improved situational awareness for the pilot.
• Reduced workloads for both controller and pilot.
• Reduced environmental impact from improved route and procedure designs.
• Reduced fuel consumption from shorter, more direct routes.

RNAV Departure Routes

For example, take the situation at Philadelphia International Airport, located in the middle of some highly popular north-south traffic lanes carrying New York and Boston traffic to or from Washington, Atlanta, and Miami. Philadelphia’s position is right underneath these flows. Chokepoints resulted from traffic departing Philadelphia, needing to wait for a “hole” in the traffic above into which they could merge. The CAASD helped US Airways and Philadelphia airport officials establish a set of RNAV departure routes that do not interfere with the prevailing established traffic. Traffic heading north or south can join the established flows at a point further ahead when higher altitudes and speeds have been attained. Aircraft properly equipped to execute RNAV procedural routes can exit the terminal area faster — a powerful inducement for aircraft operators to upgrade their navigation equipment.
Another example of an RNAV departure is the PRYME TWO DEPARTURE from Washington Dulles International. Notice in Figure 1-10 the RNAV way- points not associated with VORs help free up the flow of IFR traffic out of the airport by not funneling them to one point through a common NAVAID.