Plans to create a PBN-centric NAS — one of NextGen's primary goals — are outlined in the PBN NAS Navigation Strategy 2016, which details objectives from 2020–2030 and beyond.
The FAA has already published more than 9,000 PBN procedures and routes.
PBN procedures and routes save time and fuel while reducing emissions.
Performance Based Navigation (PBN) is an advanced, satellite-enabled form of air navigation in the National Airspace System (NAS) that creates precise 3-D flight paths.
The FAA has published more than 9,000 PBN procedures and routes, including hundreds to enhance air traffic control and flight operations at airports in metroplexes.
The benefits include lower fuel consumption and emissions as well as time savings.
If an aircraft relies on satellite positioning with GPS or Wide Area Augmentation System (WAAS), its avionics can navigate a flight path with much greater precision and accuracy than with legacy navigational systems. GPS and its augmentation systems constitute what is known internationally as a global navigation satellite system (GNSS).
PBN procedures require various avionics capabilities depending on the level of navigation precision involved. Because of mixed equipage, not all aircraft can fly the most-demanding types of PBN procedures. New aircraft usually have the latest avionics while older aircraft have a mix of avionics of various ages and capabilities. Replacing aging equipment can prove too expensive for some aircraft operators and may lead to an aircraft being retired. In other cases, an aircraft's existing equipment may be adequate for the types of flight operations planned.
PBN consists of:
- RNAV (GPS) approaches: The FAA has published more than 6,500 of these procedures for aircraft equipped primarily with GPS or GPS enhanced by WAAS. RNAV (GPS) approaches permit aircraft with the required navigation performance to operate on any desired course within the coverage of the navigation signals in use. Tens of thousands of general aviation aircraft equipped with WAAS use more than 3,700 Localizer Performance with Vertical Guidance (LPV) approach procedures at more than 1,800 airports and more than 600 Localizer Performance approach procedures (without vertical guidance) at 470 airports.
LPV provides minimums as a low as 200 feet above the ground before a pilot has to see the runway to land, which is the same as a Category 1 (Cat 1) Instrument Landing System (ILS). LPVs serve more than 1,000 airports that do not have ILS. The FAA will seldom, if ever, install a new Cat 1 ILS, opting instead for PBN approach procedures.
- RNAV Required Navigation Performance (RNP) approaches: These highly accurate approach procedures enable aircraft equipped with self-monitoring avionics to operate safely near high terrain or in congested airspace. To fly these procedures, aircrews must be trained and FAA-authorized, and aircraft must be certified. Some RNP approaches enable aircraft to fly a curved path to a runway even when other aircraft are approaching to land on parallel runways. More than 390 of these approaches are available in the NAS.
- RNAV Standard Terminal Arrivals (STAR): RNAV STAR procedures can provide a continuous descent from cruise altitude using Optimized Profile Descents (OPD) to save fuel and reduce emissions and noise. The FAA has published more than 800 RNAV arrival procedures.
- RNAV Standard Instrument Departures (SID): RNAV SIDs provide fixed, precise paths for aircraft from takeoff to en route airspace with a minimum of level offs to reduce fuel consumption and noise. Standard routings simplify navigation tasks for pilots and controllers in all weather. More than 1,100 RNAV SIDs keep departing traffic well separated from arrival traffic.
- Q- and T-Routes: The FAA is replacing high- and low-altitude routes that rely on ground-based navigation aids (navaids) with RNAV routes for use by aircraft with RNAV capability. Q-Routes can be flown using positioning from either satellite signals or Distance Measuring Equipment (DME) in case of a GPS outage. Q-Routes are replacing many Jet routes in high-altitude airspace (18,000 to 45,000 feet). T-Routes can be flown only with GNSS and are replacing many Victor routes in airspace from 1,200 feet above the surface to 18,000 feet.
The FAA also has designed a PBN route structure concept of operations to provide specified paths where needed and the capability for aircraft to fly direct from point-to-point where they are not needed. The straight paths possible with RNAV routes that do not have to zigzag from one ground-based navaid to the next reduce fuel consumption and aircraft exhaust emissions by shortening flight distance. One Washington Center sector that could fit only two Jet routes into its airspace has replaced them with four Q-Routes. Jet routes can only be located on a direct line between two ground-based navaids while Q-Routes can be located anywhere in the airspace as long as they are properly separated. With four Q-Routes instead of just two Jet routes, each of three major airports in the Washington, D.C., area now has its own feeder route, as does air traffic headed for New York airspace. The FAA has published more than 140 Q-Routes and more than 110 T-Routes.
One of the FAA's highest-priority PBN efforts focuses on 11 metroplexes — metropolitan areas where crowded airspace has to serve the needs of multiple airports. PBN departure, arrival, and approach procedures in these metroplex areas are already providing great benefits in congested terminal airspace.
The FAA has published many RNAV STAR procedures with OPD capability at metroplexes that enable aircraft to achieve greater fuel efficiency by flying closer to the airport before starting a continuous descent, which eliminates fuel-burning level offs. OPDs can be flown when available and when pilots are able to use them.
The FAA has worked closely with the NextGen Advisory Committee (NAC), a federal advisory committee composed of aviation stakeholders, to set implementation priorities. Through this collaboration, the FAA has completed PBN work in four metroplexes:
- North Texas: 67 PBN procedures
- 32 RNAV STARs
- 29 RNAV SIDs
- Six RNP approaches
- Washington, D.C.: 49 PBN procedures
- 24 RNAV STARs
- 25 RNAV SIDs
- Houston: 46 PBN procedures
- 20 RNAV STARs
- 20 RNAV SIDs
- Six RNP approaches
- Northern California: 44 PBN procedures
- 17 RNAV STARs
- 19 RNAV SIDs
- Eight Q-Routes
The FAA is preparing to publish 225 more PBN procedures in three more metroplexes, including:
- 126 at Southern California
- 68 at Atlanta
- 31 at Charlotte
In addition, Cleveland-Detroit is in the evaluation phase, while South Central Florida, Denver, and Las Vegas are in the design phase.
Denver is already using a network of RNAV STARs developed before it became a Metroplex site. These STARs have enabled RNAV (RNP), also known as RNP Authorization Required, approaches to runways since late 2013. For several years, the airport has averaged more than 1,000 RNP approaches per month.
A new FAA Established on RNP rule allows controllers at Denver to instruct pilots to make a U-turn much closer to the runway (orange) than with legacy procedures (blue). The aircraft experiences all the benefits of flying a shorter path. (Image courtesy of MITRE)
Denver uses RNP approaches that provide aircraft flying opposite the direction of landing a new method for making a U-turn to line up to land. Before RNP, controllers monitored an aircraft on radar and gave pilots a series of headings as they turned to join other aircraft already lined up on a straight-in approach to the runway. Before an aircraft under radar contact could start to turn, however, controllers had to be sure it would remain separated 3 nautical miles (nm) laterally or 1,000 feet vertically from other aircraft. This led to aircraft flying as many as 20 nm away from the runway before a U-turn was possible.
Now, due to an Established on RNP (EoR) rule change by the FAA in 2015, an aircraft can be considered established on a precisely defined, curved approach procedure with the required separation from other aircraft before it begins its U-turn to the runway. The EoR technique has enabled controllers to use curved RNP approaches more often at Denver. EoR shortens the path each aircraft takes to the runway by about 6 nm in visual conditions. As a result, Southwest, United, and Frontier airlines save fuel every time they fly one of these curved approaches.
NAC priority areas are not the only places benefiting from PBN procedures. OPDs on STAR procedures also help large airports outside of the Metroplex program, such as Minneapolis-St. Paul. More than 100 PBN projects are underway for smaller airports with unique circumstances.
The FAA is creating a PBN-centric NAS, which has always been a primary goal of NextGen. The FAA outlined its plans in the PBN NAS Navigation Strategy 2016, which details the agency's PBN objectives from 2020–2030 and beyond.
The FAA's overall objective is to use PBN throughout the NAS while employing the right type of procedure to meet the need in question. In some cases — as with metroplexes — this will include a highly structured, yet flexible, navigation pattern. The FAA recognizes the importance of involving all stakeholders — including airport operators and surrounding communities — in developing and deploying PBN procedures to ensure that community concerns are addressed. The agency is enhancing its community involvement during all phases of Metroplex and single-site PBN development, including going beyond the requirements of the National Environmental Policy Act.
In future deployments, the FAA will use a navigation service group concept to provide different scales of PBN operations for airports varying in size and levels of airspace complexity. For example, Group 1 will include the 15 busiest large hub airports in the United States. RNAV SIDs and STARs will be used at these airports to organize traffic flows, with legacy ground-based navaids used as a backup in case of a GPS outage. Groups 2 through 6 involve airports of decreasing size and varying degrees of airspace complexity. In general, airport navigation needs become less challenging in the higher group numbers. The FAA outlines the types of PBN procedures best suited for these different groups of airports.
Controllers will use new Time Based Flow Management tools to adjust the timing and sequence of aircraft arriving in the terminal area so they can smoothly execute PBN arrival and approach procedures.
The FAA's Aviation Safety Organization is developing ways to reduce runway separation requirements for EoR, which would make it possible to use the procedure in instrument meteorological conditions. It's also developing a new type of EoR that will qualify more aircraft to use it based on their existing avionics. This will help move the NAS away from inefficient radar vectors, which are still used to guide aircraft on thousands of approaches every day.
VOR ground-based navaids will remain as a navigation method for non-DME/DME aircraft during a GNSS disruption, not to create route structures. The VOR Minimum Operational Network (MON) implementation program will transition from a legacy network of more than 950 VORs to a MON of about 650 VORs by 2025. In July 2016, the FAA published a list in the Federal Register of VOR sites that may be shut down.
The FAA's planned continuous PBN improvements will create numerous benefits, including:
- Safe access to airspace near obstacles and terrain
- Vertical guidance needed for more stable and safer approaches
- Better segregation of traffic
- Reduced divergence in departure paths
- Increased efficiency in sequencing, spacing, and merging, making arrivals at the gate more predictable for airlines and their staff
- Improved predictability to enable airlines to schedule the staffing of gates more effectively
- Improved access to airports during low visibility, especially for general aviation
- Reduced flight track distance
- Reduced government spending on ground-based navaids