Stakeholders Impatient With Pace of RNP Deployment

 - November 2, 2011, 12:35 AM
ICAO resolution A37-11 calls for the implemen-tation of GNSS approach procedures with vertical guidance (APV) including Lnav-only minimums, for all instrument runway ends, either as the primary approach or as a backup for precision approaches by 2016 with intermediate milestones along the way.

Alaska Airlines started using precision required navigation performance (RNP) approaches into Juneau, Alaska, in 1996, and RNP has been used extensively by other airlines since that time. RNP is a subset of the broader, performance-based navigation (PBN) concept considered a key enabler of airspace modernization efforts in the U.S., Europe and elsewhere. In September 2007, the assembly of the International Civil Aviation Organization (ICAO) resolved that satellite-based approach procedures with vertical guidance be implemented “for all instrument runway ends” by 2016.

With acknowledged benefits of reducing track miles, mitigating noise and lowering fuel burn and emissions, you’d think RNP is off and running as a global standard. But at the PBN summit sponsored by GE Aviation in Seattle in late September and at other recent forums there was a current of frustration with the plodding pace of RNP implementation.

Most production airliners and business aircraft can fly performance-based area navigation (Rnav) flight paths using ground navaids or GPS position for reference, and many can fly the tight tolerances of RNP, which differs in requiring on-board performance monitoring and alerting. The kicker is that procedures to accommodate PBN-capable aircraft haven’t been widely developed or aren’t being used.

Steve Fulton, technical fellow with GE Aviation PBN Services, helped develop the first RNP approaches into Juneau and southeast Alaska in the 1990s as a technical pilot with Alaska Airlines (as did Hal Andersen, also with GE). He opened the fifth annual PBN summit with a progress report on ICAO assembly resolution A36-23 to implement approach procedures with vertical guidance (APV) as the primary approach or backup for all instrument runway ends by 2016.

The 2007 resolution was superseded in October 2010 by A37-11, which calls on member states to complete PBN implementation plans “as a matter of urgency,” and adds straight-in lateral navigation (Lnav)-only procedures as an exception for aircraft without Vnav capability, or for airports without local altimeter settings. The first milestone was to achieve 30 percent global deployment of PBN procedures by 2010. One year later, the deployment is half that. “It’s not enough to have resolutions,” Fulton said, “we have to have other activities to support this if we’re truly going to be successful with this goal of 100 percent (deployment) by 2016.”

U.S. Is Top Performer

The U.S. is a top performer in PBN deployment, although the FAA has been criticized for simply overlaying RNP procedures on existing routes to show progress. Fulton used a shading graphic indicating the greatest concentration of PBN approaches–from 21 percent to 50 percent of instrument runways–is in North America, followed by Central and South America with 11 to 20 percent deployment. Europe, Asia, the Middle East and Africa show faintly at 0 to 10 percent deployment.

By ICAO’s definition, there are 1,523 runways in the U.S. that are candidates for APV, of which 30 percent support vertical guidance through a ground-based GPS augmentation system, or Waas. “We have to acknowledge that there is value here,” said Fulton. “But the operators, particularly in the United States, are communicating a certain level of disappointment.”

Indeed, representatives of major operator groups expressed frustrations over RNP deployment in an October 5 hearing before the U.S. House aviation subcommittee to discuss progress toward the Next Generation Air Transportation System (NextGen). Thomas Hendricks, vice president for operations and safety with the Air Transport Association, said 90 percent of the U.S. airline fleet is capable of Rnav operations and 45 percent of RNP.

“Most of the aircraft have advanced flight management computers that allow very optimized cruise altitude and descent planning, and we’re unable to take advantage of that. And that technology has been around for a couple of decades,” said Hendricks, a former Delta Air Lines pilot and director of line operations. “I’ve flown RNP approaches myself. One of the (approaches) we’ve gained great benefit from is in Quito, Ecuador, where we improved the safety and reliability of the operation. We need to do the same thing at Chicago Midway.”


Costly Procedures

NBAA president and CEO Edward Bolen said highly accurate RNP authorization required (AR) approaches require operators to go through a costly set of approvals, with little current benefit for the GA community. “Investment in NextGen has already been made by the private sector,” he said. “The frustration is, at this point, we don’t feel we are freely, consistently and ubiquitously operating with those types of approaches.”

Lack of PBN approaches is one consideration; use of approaches that do exist is another. Much of the discussion in Seattle focused on the training and tools FAA makes available to air traffic controllers to manage mixed fleets of RNP-capable and other aircraft. The takeaway is that more work needs to be done. “A whole generation of controllers has no idea,” said Dennis Kelly, national Rnav representative with the National Air Traffic Controllers Association. Kelly said an effort is under way by US Airways in Philadelphia to have controllers observe pilots flying RNP approaches in a simulator–something Qantas has done in Australia. “When you get the controllers and pilots involved, it’s a thing of beauty,” he said.

Southwest Airlines offers a case study in the ragged implementation of RNP procedures. In 2008 the low fare carrier announced an ambitious program to equip its fleet of more than 500 Boeing 737 classics and NGs for RNP. The six-year, $175 million effort involves training 6,000 pilots to fly precision approaches and designing new procedures at the 73 airports in Southwest’s network. The network grew by 30 more airports with Southwest’s acquisition of AirTran Airways in May.

Southwest started RNP operations on January 11, and as of late September had flown 5,807 RNP AR approaches. “The bad news is those RNP AR operations are approximately one percent of our daily operations,” said Capt. David Newton, Southwest senior manager of airspace. “We have 3,400 flights a day.” The airline had developed RNP approaches at just 16 airports, 15 percent of the network.

In post-flight reports filed at the gate after shutdown, Southwest asks pilots if they have flown an RNP approach. If not, they are asked to explain why. “The vast majority of time when pilots unsuccessfully fly an RNP AR approach is because ATC takes them off the procedure or gives them a vector or reassigns them something else,” Newton said.

The airspace is designed around instrument landing system (ILS) approaches, he said, noting that “ILS” is mentioned 159 times in FAA’s ATC manual (Order 7110.65), and Rnav with respect to approaches just eight times. “RNP is just not the cultural norm,” Newton said. “The future of U.S. airspace is based primarily on NextGen. NextGen is a satellite-based navigation system and yet today, right now, it’s all about ILS (and) visual approaches.”

The situation in the U.S. is evolving. The NextGen advisory committee advising the FAA on NextGen implementation has recommended a baseline navigation capability for Part 121 carriers of RNP 0.3–the ability to stay within 0.3 nm of center line–including curved radius-to-fix (RF) flight legs. On October 4 Boeing announced a $3.1 million research task order award from the FAA for the “Greener Skies Initiative 2” to evaluate RNP procedures at Seattle-Tacoma International Airport and Boeing Field in Seattle for future application at capacity-constrained airports. The initiative builds on the Greener Skies Over Seattle project, which demonstrated Alaska Airlines’s ability to reduce emissions by 35 percent compared to conventional landings using RNP.

Fulton sees RNP playing a role in gate-to-gate air traffic management, not just as an efficient way to land a plane at a discrete airport. “Sometimes the conversations are around only the part of flight from 10 to 15 miles from the (airport), with a continuous descent approach to the runway,” he said. “That’s not the complete opportunity we have. We want to connect the cruise segment of flight with a defined, uninterrupted vertical path all the way to the runway.” With the first RNP procedures in Alaska, “that’s actually the concept we had in mind. We were cleared for approach at cruise altitude. We had an uninterrupted, ideal, optimized path all the way to the runway.”


The operational use of RNP procedures is a air traffic control option. Controllers will not reliably use RNP procedures when it pejoratively affects their workload or contributes to the complexity within their sector of responsibility. All of the approaches in the world are of little value if ATC does not say, "cleared for the approach".

Some very preliminary work has been done to create controller tools on both STARS and ARTS terminal automation systems that allow phantom targets on an extended runway centerline that represent the position of aircraft flying an RNP approach not on an ILS final. This "ghosting" or "relative position indicator" tool is a controller aid that allows them to accurately merge aircraft on different approach procedures at or near a final approach fix. Until such tools are fully developed or all aircraft are flying RNP procedures (i.e., common path, RNP use will never be fully achieved.

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RNP has some advantages such as the capability of RF turns in final, but the reality is that of all of the 3 dimensional approach types such as ILS, LPV, VNAV it normally generates the worse minimums. A standard 0.3 RNP final is incapable of minimums less than a 270 foot height above threshold, and this is before evaluation of obstacles is ever done. Additionally, RNP has to add a buffer for obstacle accuracy that the other procedure types do not use to ensure adequate safety above obstacles.

Some want to promote the "State of the Art" capability of RNP, but the reality is that the vertical guidance is using Barometric Altimetry which is technology based off 1920's or 30's?

NATCA should be concerned about this, because once these people get done complaining about there not being enough RNP procedures, they are going to complain about the controllers not clearing aircraft for these procedures. Then you can remove the “C” from ATC, because you will have none!

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