NextGen Navigational Challenges In The Air Transportation System




NextGen Navigational Challenges In The Air Transportation System

By Daniel Baxter



July 29, 2009, today Ann Calvaresi Barr, Principal Assistant Inspector General for Auditing and Evaluation, U.S. Department of Transportation addressed the Transportation and Infrastructure Subcommittee on Aviation, United States House of Representatives, on the challenges in implementing Performance Based Navigation in the U.S. Air Transportation System.  

Barr testified on the Federal Aviation Administration’s (FAA) efforts to modernize airspace through Area Navigation (RNAV) and Required Navigation Performance (RNP). Pointing out the initiatives are cornerstones of the Next Generation Air Transportation System (NextGen), which will move today’s ground-based air traffic control system to a more efficient one that relies on satellite navigation and on-board aircraft avionics.

In summary Barr stated NextGen is an important initiative to enhance capacity, reduce delays, and fundamentally change the way air traffic is managed, and RNAV and RNP are critical to its success. 40 percent of the 123 operational improvements under review by a joint Government and industry taskforce on NextGen involve RNAV/RNP.


Barr further stated the FAA has not fully laid the groundwork in areas such as developing RNP procedures that provide measurable benefits, ensuring air traffic policies keep pace with new aircraft technology, and making the necessary adjustments to air traffic control systems to accommodate new procedures. In addition, the FAA has not clearly defined the roles and responsibilities of third parties, it will be difficult to establish an effective oversight framework. Barr suggested performing a cost-benefit analyses in close coordination with all stakeholders before and after implementing RNP procedures. Establishing priorities for new routes and funding requirements for related airspace redesign projects and systems that controllers rely on to manage traffic. Developing and establishing a policy on how and to what extent third parties will be used to help support FAA’s NextGen efforts and ensure an effective oversight approach. The potential benefits of RNAV and RNP are significant and include shorter, more direct flight paths; improved airport arrival rates; enhanced controller productivity; fuel savings; and reduced aircraft noise.   


Under the current system, controller workload, radio frequency voice-communication, congestion, and the coverage and accuracy of ground-based navigational signals impose practical limitations on the capacity and throughput of aircraft in the system, particularly in busy terminal areas near major airports and around certain choke-points in the en route airway infrastructure where many flight paths converge.

Surveillance and separation of aircraft, both en route and in terminal airspace, is largely achieved by utilizing surveillance data through an extensive network of radar sites and air traffic controllers who are directly responsible for ensuring adequate separation between aircraft receiving radar services. Maintaining this separation is achieved through extensive use of voice communications between controllers and pilots over open two-way radio frequencies.

The NextGen plan will consist of new concepts and capabilities for air traffic management and communications, navigations, and surveillance that will involve: transitioning from a ground-based radar system to a more automated, aircraft-centered, satellite-based surveillance system; developing more direct and efficient routes through the airspace; improving aviation weather systems; developing data communications capabilities between aircraft and the ground to reduce controller and pilot workload per aircraft; and creating shared and distributed information technology architectures. 

Barr stated under further testimony:  The FAA and the aviation industry plan to invest billions of dollars over the next decade to bring about NextGen initiatives. To better ensure taxpayer dollars and private sector investments are used efficiently, FAA will need to carefully coordinate these efforts with industry stakeholders and within its own lines of business.

RNAV and RNP are key to NextGen’s success, but fundamental issues need to be addressed. While RNAV and RNP have considerable industry support, some stakeholders are dissatisfied with the Agency’s overall method for implementing these initiatives. Of particular concern is FAA’s practice of laying most “new” routes over existing routes and the fact that air carriers are not using them. Stakeholders and FAA also disagree on the potential role, responsibilities, and oversight of non-Government third parties in speeding the adoption of RNP. Regardless of who develops the new procedures, FAA must provide one level of safety oversight.

Barr covered two areas: (1) barriers and challenges affecting the successful implementation of RNAV and RNP and (2) the role and oversight challenges associated with use of third parties in developing new procedures. Concluded with actions needed to ensure the safe and effective implementation of RNAV and RNP.

An important part of NextGen is the establishment of new routes and procedures that rely on satellite-based navigation. FAA first implemented RNAV in 2001 and RNP in 2005 as a way to increase national airspace capacity and efficiency. Since 2001, FAA has published 270 RNAV approach and departure procedures, 159 RNAV routes, and 148 RNP approach procedures. FAA’s goals are to annually publish 50 RNAV approach and departure procedures, 12 RNAV routes, and 50 RNP approach procedures through 2013.

There are important differences between conventional route procedures and RNAV/RNP. Traditionally, aircraft have flown conventional routes adhering to the ground-based navigational infrastructure, which requires aircraft to fly in a zigzag pattern so that they can be tracked by air traffic control radar systems. RNAV and RNP increase airspace efficiency by providing more direct paths.  

For RNAV, aircraft use an on-board Global Positioning System (GPS) to fly any desired flight path without the limitations imposed by ground-based navigation systems. RNP is a form of RNAV that adds monitoring and alerting capabilities to the cockpit to guide aircraft more precisely to and from airports. Currently, RNP routes are only available to specially equipped aircraft and trained aircrews, and air carriers must meet certain qualifications to fly these RNP approaches.

Alaska Airlines pioneered RNP in 1996 to address unique terrain and weather challenges it faced in Juneau, Alaska. RNP-equipped aircraft allowed pilots to safely navigate between mountains on either side of the Gastineau Channel even during times of low visibility—this reduced the number of canceled and diverted flights into Juneau during bad weather. Alaska Airlines has implemented about 20 special RNP procedures, with annual average savings of about $14 million. It was not until several years later that FAA implemented the first public RNP procedure.

RNP procedures can be developed as public or special procedures. Public procedures are available to all users that have properly equipped aircraft; special procedures are only available to a specific air carrier for whom the procedure was designed. While FAA allows special procedures, these have historically been implemented only on a limited basis for commercial airlines. Of the more than 500 RNAV and RNP routes and procedures, 148 are public RNP procedures and 30 are special RNP procedures.  

Other countries such as Canada, Australia, China, and New Zealand have implemented RNP procedures in recent years. For example, 18 RNP departures and approach procedures deployed at the airport in Brisbane, Australia, have been flown more than 15,000 times and have provided measurable benefits, such as fuel savings and reduced flight time, to the airlines that flew them.

Significant numbers of U.S. commercial transport aircraft are already equipped for some level of performance-based navigation. Almost all U.S. air carriers are equipped to perform RNAV at the Nation’s top 35 airports; however, the percentage of equipage for the more demanding RNP capability is much lower, and the number of aircraft and flight crews equipped and authorized to fly those procedures has lagged behind. For example, 10 major air carriers have 97 percent of their aircraft equipped with RNAV capability, but only 47 percent are equipped with RNP capability, and just 23 percent are authorized to fly RNP procedures.

The FAA and industry representatives believe RNP can provide several high-value operational improvements, particularly at or around congested airports. For example, RNP can improve capacity and arrival efficiency through the use of parallel approaches to closely spaced runways and approaches to converging runways. RNP can also de-conflict operations at adjacent airports (e.g., Chicago O’Hare and Chicago Midway) through curved, final approaches to runways. Moreover, aircraft currently use a staggered, “stair-step” pattern on approach for landing, but RNP can allow a more level approach while enabling aircraft to avoid obstacles, such as buildings, near the airport.

The FAA has faced significant challenges implementing RNAV and RNP, and consequently, has not fully achieved the measurable benefits of these procedures. First, FAA’s method for implementing new RNP procedures relies heavily on existing routes; as a result, air carriers are not using them. Second, continuing operational issues and concerns over workload and training for controllers and pilots have limited the use of RNAV procedures at some airports. Finally, FAA has not yet made adjustments to key programs such as airspace redesign efforts and modernization projects that will be needed to deliver the expected benefits of RNAV and RNP procedures.

While FAA has met or exceeded its annual RNP production goals, most of the RNP procedures it has rolled out have been overlays of existing routes because the Agency’s goals primarily focus on the number of procedures produced. While overlaid routes can be deployed more quickly because they do not have to go through an extensive environmental review, they do not maximize the benefits that can be achieved through RNP procedures. As a result, industry is dissatisfied with the overall quality of RNP procedures, and they are not widely used.

Further, the FAA has not established an effective process for analyzing and measuring the benefits of new procedures from a “before–and-after” perspective. FAA program officials also do not track data that would show how often airlines use RNP procedures or reasons why they are not being used. While FAA has implemented RNP at sites recommended by a joint FAA and industry group, the sites were based on prioritization work accomplished several years ago. FAA simply followed the list without performing updated analyses to ensure the procedures would be beneficial. For example, FAA designed and implemented a procedure in Palm Springs; yet, no air carrier has used the procedure since it was implemented because its design did not provide airlines with any measurable benefits, such as a shorter flight path or the ability to fly at lower altitudes.

One RNP procedure deployed at Reagan Washington National Airport has demonstrated some benefits. The procedure allows pilots to follow a more precise path—not available through conventional or RNAV procedures—along the Potomac River while avoiding restricted airspace and obstacles. While some air carriers are approved to use this procedure, only a few are actually using it because the procedure is designed specifically for a limited number of aircraft types.

The FAA has also not updated its air traffic policies for controllers and pilots on how to use these procedures at airports with parallel runways. Due to current air traffic provisions, controllers are not yet allowed to accept an RNP procedure into the National Airspace System (NAS) at some airports with parallel runways. For example, at the Atlanta Hartsfield International Airport, FAA implemented 10 RNP procedures in May 2007 hoping that updated air traffic policies would be in place. Absent updated policies, controllers have never cleared an aircraft for landing using an RNP procedure in Atlanta. FAA is still evaluating whether the policies can safely be updated through a project at George Bush Intercontinental Airport in Houston, but this is a lengthy process that has already taken more than 4 years. FAA expects to complete this evaluation by the end of calendar year 2009.

Even if FAA updates its policies and determines that RNP can be allowed at airports with parallel runways, airline representatives told us they would not use the RNP procedures at Atlanta because they are overlays of existing conventional procedures, thus providing little or no added benefits other than a backup in the event the ground-based navigation aid shuts down.

There have been significant benefits from RNAV procedures at certain airports such as Atlanta, Dallas Fort Worth, and Phoenix. For example, RNAV departure procedures implemented at Atlanta in 2006 have increased throughput and reduced delays with a measured capacity gain of 9 to 12 departures an hour. Fewer delays have resulted in cumulative fuel savings of about $105 million for the operators who continues to limit the full use and effectiveness of these procedures. For example, at Dallas Fort Worth and Atlanta, there have been some recent operational problems related to pilots programming incorrect RNAV departure waypoints into the Flight Management System (FMS) and thus not flying the correct path.

To mitigate this problem, FAA has developed a process for pilots to read back the runway assignment and first waypoint before taking off. This process was implemented at Dallas Fort Worth on June 1, 2009, and will be implemented NAS-wide once a further safety study is completed. FAA estimates that it will be collecting data for another 30 to 60 days before deciding whether to change the process nationwide.

A longstanding operational concern is the potential impacts of “mixed equipage” where controllers will be expected to manage aircraft with different capabilities seeking to exploit different procedures. Mixed equipage presents a major challenge for the transition to NextGen. Experts believe that between 80 and 100 percent of aircraft at any given location will need to be equipped with new NextGen systems to realize benefits and limit the potential for introducing new hazards. Assessing and addressing the impacts of mixed equipage are also important for several efforts that rely on aircraft equipage, including RNAV/RNP, data link communications for controllers and pilots, and Automatic Dependent Surveillance-Broadcast (ADS-B).

A prolonged mixed-equipage environment is not desirable and will likely increase—not decrease—controller workload. This is one reason why some believe incentives will be needed to spur airlines to purchase and install new avionics. In the interim, FAA needs to develop plans to mitigate differences with aircraft equipage. This includes developing effective training for controllers and pilots and adjusting existing air traffic control systems. FAA may also have to segregate specific airspace for properly equipped aircraft.

Airspace redesign projects are critical to realize the full benefits of runways and can enhance capacity even without new infrastructure. Currently, FAA is pursuing six airspace projects nationwide,8 including a major but controversial effort to revamp airspace in the New York/ New Jersey /Philadelphia area. This project is undergoing litigation and has drawn public concerns about its environmental impact on the area. FAA plans to spend $11.2 million in airspace redesign efforts in fiscal year 2009. A level of coordination between airspace redesign projects and RNAV/RNP procedures—that currently does not exist—will be essential as procedures move beyond overlays and local operations to networking routes between city pairs such as Chicago, Illinois, and Washington, D.C. Also, FAA will have to reassess its budget and plans for airspace redesign efforts to ensure adequate and stable funding.

FAA will have to modify the automation systems, such as controller displays and related computer equipment, that controllers rely on to manage traffic in the vicinity of airports. According to FAA and others, a software enhancement that will allow controllers to merge and space aircraft is needed to obtain the benefits of new RNP procedures for enhancing airport capacity. This will also help controllers to safely manage traffic in a mixed-equipage environment. However, FAA has only begun planning and developing requirements for this capability; therefore, the cost and schedule parameters needed to adjust existing systems have not been baselined.

FAA lacks extensive and up-to-date training programs to help controllers understand and manage RNAV/RNP aircraft. This is particularly important given the large number of developmental controllers in the system. FAA’s training on new procedures consists of briefings rather than formal courses on RNAV/RNP. As FAA moves toward implementing more advanced RNP routes, extensive training will be required for controllers to gain confidence in their ability to use RNAV/RNP. As one industry expert pointed out, simulators will be needed to support the training of the controller workforce. Without adequate controller training, RNAV/RNP cannot be successfully introduced.

The role of third parties in developing RNAV/RNP procedures is unclear, and industry representatives are skeptical of FAA’s ability to deliver the more complex procedures in a timely manner. Any use of third parties will inevitably carry a new layer of safety concerns, and FAA has yet to establish a coordinated oversight framework to mitigate potential operational risks.

FAA entered into agreements in 2007 with two non-Governmental third parties to design, integrate, test, and validate public RNP procedures. According to FAA, the intent of the third-party initiative was to provide industry or the international community with FAA-qualified vendors who could develop procedures within and outside the United States where existing infrastructure was lacking or where the new procedures would not create complex integration and implementation issues.

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