A fundamental American value is the notion that ability and performance determine whether an individual can navigate beyond his or her starting position. We cherish the idea that with the right ability and performance, anyone can move freely from one station in life to another-the sky is the limit. You might think of performance-based navigation (PBN) as the aviation expression of that value. Traditionally, operations in the National Airspace System (NAS) have been restricted to “station-referenced navigation systems,” which limit an aircraft to flying over standard ground-based navigation aids such as very high frequency omnidirectional range (VOR) and non-directional beacon (NDB) facilities.
The Sky’s the Limit with PBN. Now, however, the advent of the “coordinate-referenced” PBN means that an aircraft is no longer restricted to what is often a circuitous station-to-station journey. Unlike the station-referenced system, which specifies required technologies, such as VOR, or particular avionics, such as an ILS receiver, a PBN system simply defines the aircraft navigation capabilities and required performance necessary to operate on a given air traffic route, instrument procedure, or in a defined airspace. Given the right supporting infrastructure, such as the Global Positioning System (GPS), any aircraft whose navigation system meets the defined performance and functionality requirements has access to that route, procedure, or airspace. The foundation concepts for PBN are area navigation (RNAV) and required navigation performance (RNP). Let’s take a look.
RNAV Means Flexibility. Area navigation is not a new concept. It first appeared in the United States in the 1960s, with the first RNAV routes published in the 1970s. In simple terms, RNAV is a navigation method that allows an aircraft to operate on any course within a network of navigation stations, rather than navigating directly to and from the stations. More formally, it is a method of navigation which permits aircraft operation on any desired flight path within the coverage of ground or spaced-based navigation aids or within the limits of the capability of self-contained aids, or a combination of these. For example, RNAV can use the following:
- Station-based systems, such as distance measuring equipment (DME);
- Coordinate-based systems, such as GPS;
- Or, self-contained systems, such as the inertial navigation systems (INS) found in large air transport aircraft.
Regardless of the system used to provide area navigation capability, the benefits of RNAV are clear and the recent standards developed for RNAV operations account for modern aircraft capabilities. The advantages of current RNAV routes and procedures include greater safety, navigational flexibility, shorter routes and reduced time en route, less fuel usage, and reduced dependence on ATC radio transmissions.
RNP = RNAV + Navigation System Performance Monitoring and Alerting. From an operational point of view, RNP means that the aircraft, or the aircraft in combination with the pilot, provides onboard monitoring and alerting of navigation-system performance. In essence, RNP is RNAV with enhanced knowledge of how the aircraft navigation system is performing. This onboard monitoring and alerting capability improves the pilot’s situational awareness, and it can also enable reduced obstacle clearance or closer route spacing without ATC surveillance. If your aircraft is equipped with GPS, you will recognize RAIM- receiver autonomous integrity monitoring-as an example of this safety-critical characteristic. With respect to airspace or a specific operation, the associated RNP states the navigation performance necessary for operation in that airspace. This RNP is typically expressed as a distance in nautical miles from the intended center-line of a procedure or route.
The Strategy for PBN. In 2006, the FAA published its Roadmap for Performance-Based Navigation, which focused on the continued implementation of PBN in the United States. The information in this plan has since been incorporated into the annual FAA NextGen Implementation Plan, the most recent version of which was published in March 2010. Over the past decade, the FAA has worked with its global partners to develop worldwide standards for PBN in the interest of improved safety and reduced costs to the aviation community. The result of much of this work is embodied in the International Civil Aviation Organization (ICAO) PBN Manual, which, among other things, contains aircraft and operational standards categorized as “navigation specifications.”
It’s likely you’re already familiar with a number of U.S. operations that are reflected in the manual. For example, if you’re qualified to fly an approach titled RNAV (GPS) or GPS, then you’ve already met the requirements for what is now being called an “RNP Approach.” ICAO criteria for RNAV 1 departure and arrival procedures, RNAV 2 routes (Q and T), and RNP Authorization Required (AR aka SAAAR- Special Aircraft and Aircrew Authorization Required) approaches also match our U.S. operations. Additional standards for more advanced RNP operations will likely be published in the next year or so and the FAA will work to get the word out regarding any changes via updates to Advisory Circulars, the Aeronautical Information Manual (AIM), and other publications.
The Pilot’s Role. PBN operations offer enormous potential for improved safety, access, capacity, predictability, and efficiency but also demand sound preparation and strict maintenance of the procedure center-line. In addition, pilots must possess a strong working knowledge of their aircraft navigation system and the fundamentals of RNAV. So, as with any navigation system, the success of PBN ultimately depends on- you guessed it-the pilot. (FAA Safety Briefing – MayJune 2010)