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From your friends at  2006 - Reproduction without permission is prohibited.

One of the main concerns regarding air traffic management is the continuing growth of demands on airspace capacity and the need for the best use of the available airspace.  In order to compensate for this continuing growth, many airports are building more runways, ramps, and facilities to accommodate this increase.  For example, Atlanta's Hartsfield-Jackson International Airport (ATL), the world's busiest airport, is commissioning a new runway in 2006.  However, even building a new runway will not solve the epidemic of increasing air travel for the future.  The Federal Aviation Administration (FAA) has been working hard to implement a better standardization plan for this increase in capacity, not only in Atlanta, but across the United States.  One concept that is currently in production to help solve this issue is known as Required Navigation Performance or RNP.  RNP is a set of standards that measure performance accuracy of aircraft in a certain defined airspace, or along a predefined route, approach, etc.  One example of RNP standards could be to decrease the spacing buffer of air traffic entering into Atlanta's airspace, thus increasing the capacity of aircraft on approach for landing.  Instead of spacing aircraft 4 nautical miles apart, this could be reduced to say 1.5 nautical miles, which would obviously open up more space for aircraft.  However, you may be wondering how this could happen without compromising safety.  One answer to that is a method known as RNAV or Area Navigation. 

So what is RNAV?  Area Navigation (RNAV) can be defined as a method of navigating an aircraft on any desired course within the circular coverage of station-referenced navigation signals, such as VOR stations.  In other words, RNAV allows the pilot of an aircraft to create a virtual waypoint anywhere along their flight path as long as they are within a certain distance of a VOR and can still receive a signal from that VOR. 
For most aircraft this is accomplished by having a combination of equipment.  As a pilot you will need some form of Distance Measuring Equipment (DME) to calculate the distance from the VOR station to the position of your virtual waypoint, then you will need some form of equipment to calculate the longitude and latitude of your virtual waypoint in relation to the VOR station, such as Global Positioning System (GPS) or an Inertial Navigation System (INS). If you just have standard VOR receivers, you can only navigate TO/FROM a VOR. However, in order to utilize RNAV, your aircraft must have appropriate equipment onboard in order to compute these virtual waypoints - because RNAV equipment can handle these "virtual" waypoints in a way that standard navigation equipment cannot.  RNAV procedures are currently in full swing at Las Vegas, Philadelphia, and in April of 2005, 13 Area Navigation or RNAV departure procedures and 4 new arrival procedures went into full operation at Atlanta's Hartsfield-Jackson International Airport. These procedures allow about 90 percent of the departure and arrival traffic at ATL to utilize this technology assuming they have the needed on-board advanced avionics systems.

Some of the advantages of using RNAV include reducing fuel costs, arrival and departure times for the air carriers, as well as reducing the workload of ATC.  For example, let's follow a simple flight to show some of the benefits of RNP-RNAV routes and how this method might use it. In the firgure to the right, a departure and an arrival point is shown, with some VORs in between.  If a pilot navigates via victor airways from the departure to the arrival point they would have to fly TO/FROM different VOR stations in different directions.  This increases the time and distance traveled from departure to arrival and burns more fuel.  In addition, ATC must monitor this traffic more closely to facilitate the separation of aircraft over a larger section of airspace.  However, by using an RNAV route pilots alone could merely move the existing VOR locations to more convenient virtual locations, therefore straightening their flight path, reducing travel time, distance, and fuel burn as well.  So, in this example, the pilot would inform the onboard navigation systems that he/she wanted to establish the first waypoint 9 nautical miles from VOR 1 along the 180 degree (due south) radial.  Then the pilot would simply enter the other waypoints into the computer system just as the first one and the onboard computer would calculate this flight path and you are on your way.  However, due to unforeseen circumstances such as thunderstorms and various wind speeds and direction, an aircraft may or may not be able to hold a straight course along the fixed flight path generated by the RNAV equipment on board.  Therefore having a buffer zone to each side of that path, put in place by RNP standards would give the aircrew some flexibility en route without compromising safety or increasing the workload of ATC.

Now that we have seen the advantages of time saving while using RNP-RNAV procedures, let's imagine what might happen if all 1300 daily arrivals into Atlanta could save just 3 minutes of flight time by flying an RNAV route.  This would equate to a savings of nearly 24,000 hours per year, and that accounts for just arrivals into Atlanta.  Delta Airlines has its largest fleet at Atlanta's Hartsfield-Jackson International Airport, and according to their calculations, the use of RNAV alone could save them over $30 million dollars a year, while the Federal Aviation Administration (FAA) reports that the airline industry as a whole could save over $750 million dollars a year with the further implementation of RNAV. 

The current roadmap of the FAA is to have RNAV become the primary means of navigation in U.S. airspace.  In fact, Atlanta, Las Vegas and Philadelphia have already implemented RNAV procedures, with additional RNP procedures becoming available as more aircraft are equipped with advanced technologies.  The plan also includes removing some ground-based navigation aids, routes and procedures from service starting in 2010.  According to the FAA, Required Navigation Performance and RNAV airspace and procedures, coupled with increasing aircraft fleet usage of GPS, will form the foundation for moving towards a satellite-based air traffic management system in the United States within two decades.

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