Performance Based Navigation Expands
Year after year, the elements of Performance Based Navigation (PBN) have been mainstays of the Next Generation Air Transportation System, and account for most of the benefits NextGen has provided so far. PBN implementation continued to grow during 2012.
The most basic PBN capability is Area Navigation (RNAV), which uses performance-based sensors or procedures, such as GPS or triangulation using Distance Measuring Equipment, and onboard computing for greater precision and flexibility in establishing a flight path, improving efficiency. This capability can be used on a Standard Terminal Arrival (STAR), on a Standard Instrument Departure (SID) and during cruise flight (Q-routes at high altitude and T-routes at lower altitudes near terminal areas). As of March 7, 2013, the FAA had published:
- 448 RNAV SIDs;
- 238 RNAV STARs;
- 94 Q-routes; and
- 80 T-routes.
Some STARs are structured as Optimized Profile Descents (OPD), in which aircraft fly arrivals that minimize the time they spend in level flight. This enables the aircraft to operate at reduced engine power settings throughout the arrival, minimizing fuel consumption. The most prominent use of OPDs to date is in Seattle's Greener Skies initiative, from which the primary airline user, Alaska Airlines, estimates reductions of 2.1 million gallons of fuel and 22,000 metric tons of aircraft exhaust emissions per year. Dollar savings depend on the price of fuel.
When computer equipment aboard the aircraft monitors RNAV performance, the aircraft can attain a higher level of precision and fly Required Navigation Performance (RNP) procedures. Advanced versions of RNP can support curved approaches to airports, enabling airspace designers to relieve conflicting approaches to airports that are close to each other. As of March 7, the FAA had published 360 RNP approaches.
RNAV procedures are central to the Optimization of Airspace and Procedures in the Metroplex (OAPM) program, in which the FAA and stakeholders combine RNAV procedures and airspace redesign to increase efficiency and improve environmental performance in complex airspace encompassing multiple airports (See NextGen Today in the 2013 update to the NextGen Implementation Plan). Apart from OAPM, the FAA published many procedures during 2012 and early 2013 that will provide significant improvements at major airports. For example, Denver has 15 new RNAV SIDs, 17 RNAV STARs and 12 RNPs. Other publications include 12 SIDs, 4 STARs and 6 RNPs at Nashville; 3 STARs and 6 RNPs at Portland, Ore.; and 13 SIDs, 12 STARs and 6 RNPs at St. Louis.
RNAV SIDs and STARs have been implemented at major airports across the NAS during the last several years. Analysis of utilization rates indicates that more than 40% of the flights operating into the 10 busiest airports are using RNAV STAR procedures. At key metroplex airports such as Washington Reagan National, RNAV STARs usage is more than 80%. Post-implementation analyses show that fuel savings are being achieved for flights using these procedures. RNAV SIDs are also coming online in various locations. As soon as 16 new RNAV SIDs were activated in March 2012 at Memphis International Airport, more than 95% of departures used them. For RNP approach procedures, utilization rates are starting to increase. One key aspect of approach procedures is that they are designed for use in specific weather conditions and runway configurations. Some airports, such as Chicago Midway, have successfully used RNP approach procedures to enable operators to land in operating conditions that would have prevented a landing in the past, or would have had other adverse impacts such as ground delays at neighboring airports.
The Wide Area Augmentation System (WAAS) Localizer Performance with Vertical Guidance (LPV) offers performance comparable to an Instrument Landing System (ILS) without the infrastructure cost (see Making a Difference for General Aviation in this edition of the NextGen Implementation Plan). As of April 4, 2013, the FAA had published 3,100 WAAS LPV approaches to 1,077 ILS runways and 2,023 non-ILS runways. The agency implemented 330 of these approaches in FY 2012 — 75 at ILS runways and 255 at non-ILS runways.