With its proven ability to ease air-traffic congestion, save fuel and facilitate approaches to airports that are encumbered by weather or terrain, performance-based navigation (PBN) is now an option being considered by airlines and Air Navigation Service Providers (ANSP) for many different airports in all regions of the world — not just those on mountaintops in Tibet.
Assisting those airlines and ANSPs in developing Required Navigation Performance (RNP) approaches are a number of companies. In the United States, four organizations have FAA authorization under Advisory Circular 90-101 "Approval Guidance for RNP Procedures with SAAAR" (Special Aircraft and Aircrew Authorization Required) to assist airlines and ANSPs in developing RNP procedures: Jeppesen, Naverus, Honeywell and Boeing. Those companies also have approval to develop "private procedures," built outside public criteria established by FAA, to take advantage of special capabilities in an aircraft such as a head-up display (HUD) where the HUD is needed to fly down to the minimums designed in the RNP procedure.
The concept of approving a handful of RNP consultants is not unique. A Designated Engineering Representative has authority from FAA to approve certain designs in engines, structures and other disciplines, for example. There are also approved check airmen who can conduct flight checks and instruction. The RNP process, however, goes way beyond training a single individual to take over an FAA function.
"The power of RNP SAAAR is that it opens up the procedure designer’s toolbox," said Chad Cundiff, Honeywell vice president of crew interface products. "A WAAS (Wide Area Augmentation System) LPV (lateral precision vertical) approach has limitation; you can’t do a precision curved approach. The value of a precision curve is that the airspace you have to protect on either side of the airplane is smaller."
Creating the navigation charting piece of an RNP approach procedure is a multifaceted process.
"You have to capture data and convert it to an ARINC 424 format, and then work that into a navigational database that can be displayed into the cockpit," said Nasos Apostolopoulos, enterprise manager of aviation data with Jeppesen. "It is rendered either on paper or in electronic form. The provider of the service has to create the database, provide the chart, and, going upstream, has to develop a procedure for a specific airport. And once you print that information, you must maintain it."
Updates are also required for constantly changing details like airport communications frequencies, elevations around the airport after new surveys, runway extensions and new lights.
"The mountains are always there but all the things that humans add to the equation change constantly," said Andy McDowell, director of airspace and airports at Jeppesen Atlanta.
Another element in the procedure designer’s toolbox is the ability to develop RNP procedures for guided, missed approaches. Because RNP SAAAR is based on multiple navigation sensors, the loss of a sensor like GPS — or an engine, for that matter — doesn’t preclude continuation of the RNP approach.
"One of the things we look at is the possibility that an aircraft could lose an engine and climb performance is not at full capacity," said McDowell. "We’ll build the path of a missed-approach segment of a procedure so the aircraft can still extract itself from the airport environment at a deteriorated rate."
Airline operators themselves have to be approved for RNP procedures. "The operator needs an approved training program, policies and procedures, and operational specifications to use those procedures," said Matt Vacanti, director of operators programs for Naverus, of Kent, Wash. "They have to have dispatch policies and a program to monitor navigational data on the airplane."
Because of the complexity of the work, few airlines — let alone business jet operators — attempt to tackle the process without the assistance of one of the four FAA-approved RNP consultants.
"Our job is helping the operator get to compliance," said Cundiff.
Honeywell has focused much of its RNP consulting efforts on business aviation. "With bizav, you don’t have an in-housing training department, so we work with FlightSafety (International) to define an RNP training curriculum. The key to getting operational approval is that pilots have to be trained on the uniqueness of RNP."
Terrain And Traffic
There are 100 or fewer airports in the world today for which RNP procedures have been developed, located mainly in Australia, Canada, the United States and China. Those airports, in turn, are primarily situated in high terrain, or where aircraft on approach must thread down a mountainous river valley, or in restricted airspace like Washington, D.C., where pilots can’t cross the east bank of the Potomac River where important monuments and buildings are located.
In the RNP world, those locations are the low-hanging fruit, according to Rob Holleran, Jeppesen chief technical pilot. Holleran is a member of the FAA Advisory Board for PBN and participated on the task force that developed FAA Advisory Circular 90-101. But more and more airlines and ANSPs are looking at RNP procedures as a way to reduce their "pain points," particularly around congested airports in big cities like Atlanta, Dallas, New York and Hong Kong.
"Airlines aren’t flying RNP approaches because it is high tech, but because it has real benefit," said Vacanti. "It saves fuel, saves time, provides schedule reliability improvements, improves load capacity by giving you the ability to get in and out of certain airports with more weight, and lets you fly in weather and conditions that were impossible before."
For example, Naverus has worked with Southwest Airlines on bringing RNP procedures to what, on the surface, may seem to be an obstacle-free route between Dallas and Houston.
"Mountains are hard obstacles, but RNP can also be used for soft obstacles," said Josh Kendrick, Naverus senior technical pilot. "Soft obstacles would be airspace areas. Dallas and Houston have two large airports and Southwest flies to the secondary airports, Love and Hobby. On that route, there is a mountain of airspace in the sky instead of a mountain of granite. With RNP, you can bend flight paths to help manage traffic flow."
Using RNP procedures between Dallas and Houston, Southwest realized an 8 percent savings in fuel in one test, according to Kendrick.
In another example, operators that fly into the three New York City metro-area airports — LaGuardia, JFK and Newark — are looking at using RNP procedures to draw a tight path around each of the runways in order to deconflict traffic going to each respective airport.
Boeing is also addressing the challenge of developing RNP procedures for airports that are less terrain challenged than they are traffic challenged, although Boeing works the other issue, too, as evidenced by its recent work with Air China in Lhasa, Tibet.
"We’re working with Copa Airlines in Panama to implement RNP at Tocumen Airport outside Panama City," Panama, said Steve Duenkel, performance-based navigation program manager in Boeing’s Navigation Services group. Located on the south coast of Panama, Tocumen is not terrain challenged. The challenge is working with the regulator because it is an airport shared by many users with all different capabilities.
"Air-traffic controllers like to follow the same set of game plans every day," Duenkel said. "Airline X may be flying RNP, but everybody else is doing it differently, so integration is the challenge. The technology is the easy part."
At the same time, there’s no denying the importance of the technology, because the capabilities of today’s flight management systems (FMS) from companies such as GE Aviation and Honeywell are what have given regulatory bodies like FAA the confidence to proceed with RNP procedures.
"What we watch is how precisely the navigation system can guide the aircraft, and how well the aircraft can maintain its defined path," said Kendrick. "Getting air-traffic control clearance to fly these approaches is key. Air-traffic control wants predictability. With a defined flight path you can get that predictability."
The capability was probably always there; it just took some smart people to figure out how to bring it all together.
"All this equipment like FMS and GPS have been around for a while," said Naverus spokesman Ken Shapero. "Now we’re learning how to put it together and create procedures to take advantage of the technology. It’s like classic VOR ground-based navigation. How long was it around before someone put DME (distance measuring equipment) with VOR and created waypoints," he said.
Such predictability works even though the number of airports and aircraft approved for RNP procedures is small.
"You don’t have to be all in or all out," said Kendrick. "It works in a mixed environment, and improves the performance of non-RNP operations by freeing up airspace for other aircraft.
"It’s like the missing link between Lucy and Homo erectus," he said, referring to the upright-walking mammals that preceded Homo sapiens. "You don’t go from all conventional navigation to all RNP in one step. But by doing it now we’re creating benefits for people who aren’t RNP equipped."
Naverus is working with Sweden’s ANSP, for example, to study how that nation can transition over the next decade to a system with just partial performance based navigation to one that wholly embraces the capabilities.
Similarly, China is working to develop and publish its own national roadmap for PBN. Boeing is working with the Civil Aviation Administration of China (CAAC) on that program. "China has realized that an efficient airspace is an essential element to economic growth," said Duenkel.
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