Performance Based Navigation (PBN) is an advanced, satellite-enabled form of air navigation that creates precise 3-D flight paths. The FAA has published more than 9,300 PBN procedures and routes. These procedures and routes offer a number of operational benefits, including enhanced safety, increased efficiency, reduced carbon footprint, and reduced costs.
The FAA is beginning to monitor an aircraft's trajectory including its time at points along these 3-D paths so the agency can anticipate the timing of arrivals at major airports. The FAA, airlines and foreign air navigation service providers will exchange flight trajectory data in real time on all flights in progress as the agency moves to Trajectory Based Operations (TBO) over the United States and offshore. Under TBO, the FAA will use the aircraft trajectory to manage all phases of flight tactically and strategically.
Performance-Based Navigation (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.
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 (or similar systems in Europe and Asia) and their augmentation systems constitute what is known internationally as a global navigation satellite system (GNSS).
Aircraft with PBN avionics can use thousands of approach procedures.
PBN in the National Airspace System (NAS) mainly consists of:
- Area navigation (RNAV) standard instrument departures (SID): RNAV SIDs provide fixed, precise repeatable 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 1,200 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 routes that use RNAV specifications for use by aircraft with RNAV capability. T-Routes can be flown only with GNSS and are replacing many Victor routes in airspace from 1,200 to 18,000 feet. 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 from 18,000 to 45,000 feet. The FAA has published more than 100 T-Routes and more than 145 Q-Routes.
- 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 860 RNAV arrival procedures.
- Required navigation performance (RNP) approaches: The FAA has published more than 7,000 of these procedures. They were previously identified by the FAA as RNAV (GPS) until the International Civil Aviation Organization changed this nomenclature. RNP approaches are for aircraft equipped primarily with GPS or GPS enhanced by WAAS. RNP 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 3,800 localizer performance with vertical guidance (LPV) approach procedures at more than 1,880 airports. The majority of these airports do not have an instrument landing system (ILS) procedure. The FAA has also published more than 650 localizer performance approach procedures without vertical guidance at more than 490 airports.
- RNP approaches with authorization required (AR): These highly accurate approach procedures enable qualified operators with equipped aircraft to fly with great precision on the same flight path every time near high terrain or in congested airspace. To fly these procedures, aircrews must be trained and authorized by the FAA to fly RNP, and aircraft must be certified. Some RNP AR approaches enable aircraft to fly a curved path to a runway even when other aircraft are approaching to land simultaneously on parallel runways. More than 390 of these RNP AR approaches are available in the NAS.
- RNP approaches with LPV: These provide 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 I ILS. LPVs serve more than 1,120 airports that do not have ILS. The FAA will seldom, if ever, install a new CAT I ILS, opting instead for PBN approach procedures.
The FAA also has designed a PBN route structure concept of operations to provide specified repeatable 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 reduce fuel consumption and aircraft exhaust emissions by shortening flight distance since aircraft no longer have to zigzag between ground-based NAVAIDs. One Washington En Route Center sector has replaced two Jet routes with four Q-Routes. Jet routes can be located only 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 two Jet routes, each of three major airports in the Washington, D.C., area has its own feeder route, as does air traffic headed for New York airspace.
One of the FAA's highest-priority Performance Based Navigation (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 metroplexes are providing great benefits in congested terminal airspace.
The FAA has published many area navigation (RNAV) Standard Terminal Arrival (STAR) procedures with optimized profile descent (OPD) capability. This enables aircraft to achieve better fuel efficiency by flying closer to the airport at the more fuel-efficient altitude before starting a continuous descent, which eliminates fuel-guzzling level offs.
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 seven metroplexes:
- Atlanta: 68 PBN procedures and routes
- 18 RNAV standard instrument departures (SID)
- 14 RNAV STARs
- 13 RNAV GPS T-routes
- 23 RNAV Q-routes
- Charlotte: 33 PBN procedures
- 15 RNAV SIDs
- 18 RNAV STARs
- Houston: 46 PBN procedures
- 20 RNAV SIDs
- 20 RNAV STARs
- Six required navigation performance (RNP) with authorization required (AR) approaches
- Northern California: 42 PBN procedures and routes
- 19 RNAV SIDs
- 15 RNAV STARs
- Eight Q-Routes
- North Texas: 67 PBN procedures
- 29 RNAV SIDs
- 32 RNAV STARs
- Six RNP AR approaches
- Southern California: 132 PBN procedures and routes
- 52 RNAV SIDs
- 42 RNAV STARs
- 1 T-route
- 16 RNP approaches
- 21 RNP AR approaches
- Washington, D.C.: 49 PBN procedures
- 25 RNAV SIDs
- 24 RNAV STARs
In addition, Cleveland-Detroit and Denver are in the evaluation phase, while South Central Florida and Las Vegas are in the design phase. Denver is using a network of RNAV STARs developed before it became a metroplex. These STARs have fed traffic into RNP AR approaches to runways since late 2013. For several years, the airport has averaged more than 2,000 RNP approaches per month.
Aircraft on radar vectors at Houston George Bush Intercontinental fly well away from the airport before turning to land. With PBN (right), once established on RNP, the aircraft can make a U-turn closer to the runway to save time and travel distance.
Denver and Houston use RNP approaches that provide aircraft flying opposite the direction of landing a new method to reverse course to line up to land, called Established on RNP (EoR). 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. This legacy procedure is still in use, but before an aircraft under radar contact can start a turn, controllers have to be sure it will remain separated 3 nautical miles laterally or 1,000 feet vertically from other aircraft. This leads to aircraft flying as many as 20 nautical miles away from the runway before it is possible to reverse course.
Due to an EoR rule change by the FAA in 2015, an aircraft that is suitably equipped can be considered established on a precisely defined, curved approach procedure with the required separation from other aircraft for simultaneous approaches to parallel runways before it begins its 180 degree turn to the runway. EoR has enabled controllers to use curved RNP approaches more often at Denver and Houston. EoR shortens the path each aircraft takes to the runway by about 6 nautical miles in visual conditions. As a result, Frontier, Southwest, and United airlines save fuel every time they fly one of these curved approaches, and passengers aboard these flights touch down earlier.
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 Performance Based Navigation (PBN)-centric National Airspace System (NAS) — a primary goal of NextGen. The FAA in 2016 outlined its plans in the PBN NAS Navigation Strategy, which details the agency's PBN objectives from 2020 to 2030 and beyond.
The FAA will move toward time-based management of air traffic so that aircraft can be merged into predictable streams of airplanes approaching terminal airspace. The goal is to have aircraft begin PBN arrival and approach procedures in a steady sequence without any delay. Previously, controllers managed separation of aircraft based on knowing where an aircraft was at any given time. With Trajectory Based Operations (TBO), the FAA will manage traffic on the basis of knowing when and where an aircraft will arrive at critical points along its flight from departure to destination. Time-based management and the PBN-centric NAS will enable TBO in the future.
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.
Seven metroplexes with more than 170 Standard Instrument Departures minimize level offs, fuel burn, and noise on departure.
In future deployments, the FAA will use a navigation service group (NSG) concept to provide different scales of PBN operations for airports varying in size and levels of airspace complexity. For example, NSG Group 1 will include the 15 busiest large hub airports in the United States. Area navigation Standard Instrument Departures (SID) and Standard Terminal Arrivals (STAR) will be used at these airports to organize traffic flows, with legacy ground-based navigation aids (NAVAIDs) used as backup.
NSG Groups 2–6 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, sequencing, and spacing of aircraft arriving in the terminal area so they can smoothly execute PBN arrival and approach procedures.
The FAA's Aviation Safety Organization has developed ways to reduce runway separation requirements which are making it possible to use required navigation performance (RNP) procedures in an Established on RNP operation in adverse weather, also known as instrument meteorological conditions (IMC). Controllers at Houston George Bush Intercontinental conducted the first EoR operation in IMC in June 2017. EoR will help move the NAS away from inefficient radar vectors, which still are used to guide aircraft on thousands of approaches every day.
Legacy VOR ground-based NAVAIDs will remain as a navigation method for distance measuring equipment (DME) or non-DME aircraft during a global navigation satellite system 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
- 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