By John McHale

The aerospace industry is moving from rules-based operations to performance-based operations (PBO) to be more efficient in navigation, flight control, synthetic vision, and fuel consumption challenging avionics designers to upgrade their current systems to enable PBO especially in the area of required navigation performance (RNP).

RNP/PBO will also enable the air traffic management (ATM) shift to the Federal Aviation Administration's (FAA'S) Next Generation Air Transportation System (NextGen) and Single European Sky ATM Research (SESAR).

"PBO enables aircraft to fly along any trajectory only limited by own navigation and time performance," says Lars Lindberg, president of AvTech AB in Sweden. "This gives the possibility to follow a trajectory that is closer to the airlines preferred trajectory and thus reducing operating cost and minimizing environmental impact. The current ATM system is limited by its rules and current tools to sequence traffic.

"An optimum continuous descent approach (CDA) approach cannot be provided in high density environments due to the lack of sequencing tools enabling the use airborne functions such as RTA," Lindberg continues. "Once these are created, current aircraft capability provides possibilities for PBO to take the aircraft closer to its optimum in daily operations. In low capacity environments the advantages of PBO and RNP are available today."

Complimenting NextGen and SESAR

"The ICAO has urged its member states to establish an implementation plan for performance-based navigation such as RNP," Lindberg says. "At the same time NextGen and SESAR are accelerating its development and also validatng the use of current equipment. AVTECH together with Swedish operator Novair and ANSP LFV as well as Airbus and EGIS Avia implemented last year a RNP Approach to Stockholm Arlanda within the MINT project. The RNP Approach was flown with and without time constraints. Aircraft data from standard approaches as well the MINT approach was analyzed and normalized.

Lindberg states the average savings under the project was 165 kilograms and 525 kilograms of CO2. "At TMA entry, when flying with time constraint the average error was 8.4 sec.

"The objective of MINT was to demonstrated the benefits of PBO using current Airbus equipment, he continues. SESAR has now issued a Call For Tender for AIRE validation projects. We expect to see similar projects taking shape."

Within the MINT program AVTECH used their PBO Analyzer tool, which is being developed continuously to meet the demands of RNP Analysis, Lindberg says. It also analyzing Qantas RNP operations continuously and is "available to any operator using RNP Approaches. The tool can be connected to the airlines FOQA software as an extension.

"In other parts of the world, such as Australia, RNP is being used extensively. And we expect projects taking into account the longitudinal navigation, ie. time to take shape both in the U.S. and elsewhere," he says.

Lindberg points out that for all of the projects listed it is critical that benefits be quantified "in order to reach acceptance from various stakeholders. Data analysis based on aircraft data will remain a key as to correctly quantify benefits in terms of noise, fuel, and emissions."

Upgrading avionics equipment to enable RNP

"Modern integrated avionics systems are by and large very capable with respect to RNP" says Adam Evanschwartz, principal marketing manager, Commercial Systems for Rockwell Collins in Cedar Rapids, Iowa. "Performance-based navigation advancements underway now and many of those forecast for the future are providing new operational benefits that leverage the already extremely capable on board systems. One substantial challenge facing the industry is ensuring that airspace and air traffic management policy and procedures keep pace with aircraft capabilities.

"RNP is here and now," says Chad Cundiff, vice president of Crew Interface Products at Honeywell Aerospace in Phoenix. "We have been actively upgrading are avionics systems for air transport, regional, and business aviation for PBO/RNP," having provided RNP SAAAR capable systems for Boeing, Airbus, Embraer, and Gulfstream with upgrades of other aircraft types in process, he adds.

Cundiff says there are a number of key points for avionics designers to be aware of regarding RNP.

"RNP requires multi-mode navigation, ensuring that any loss of any single navigation system (such as GPS) that sufficient navigation capability is available to complete the approach or the missed approach," Cundiff says. Precise flight path control is needed to maintain the aircraft inside the very tight corridors associated with RNP SAAAR, he adds.

"Sensor selection, integrity monitoring, and flight path display are also critical items to ensure adequate capability to conduct a RNP SAAAR approach," Cundiff continues. "In addition, an operator must receive special training and operational approval, and must do additional analysis on their database.

For the transition to performance-based navigation Rockwell Collins engineers recently introduced a Flight Management System software upgrade for integrated flight deck systems currently in the field, Evanschwartz says. "It enables a new type of curved flight track called Radius-to-Fix Legs (RF Legs) along with other navigation upgrades including SBAS LPV approach capability."

"RF Legs enable unique flexibility in the design of PBN arrival, departure, and approach procedures and are described in FAA AC 90-105 Appendix 5 "Advanced Features," Evanschwartz continues. "The list of aircraft types on which this software upgrade is certified is growing rapidly given the market interest in performance-based navigation and related advancements. Certain types of RNP operations, such as some RNP approaches with Authorization Required drive the need for additional changes within the avionics systems."

Rockwell Collins avionics systems that enable performance-based navigation include the company's Global Navigation Satellite Systems (GNSS) sensors, which provide " very accurate and reliable positioning information," Evanschwartz says. "For example, Southwest Airlines is equipping more than 200 Boeing 737 Classic aircraft with our GPS-4000S for RNP operations."

Also Rockwell Collins's integrated flight deck systems for business aircraft and regional airline aircraft are capable of many types of performance-based navigation including RNP Approach Operations as defined in FAA Advisory Circular 90-105, Evanschwartz continues. "With these integrated systems Rockwell Collins supplies the RNP-capable flight management systems, information displays, automatic flight control systems, and SBAS-augmented GNSS sensors.

Cundiff says the different Honeywell avionics optimized for RNP include:

-Inertial Reference Systems – which provide a hybrid inertial-GPS navigation solution that enables the dual navigation solution that provides the best possible access to RNP procedures;

- GPS systems that provide GPS position to the aircraft for RNP/PBO operations;

- flight management systems which provide flight path control to fly RNP procedures, and manage performance and system integrity;

-the Enhanced Ground Proximity Warning System, which provides an additional layer of safety by alerting the flight crew to nearby terrain;

- displays, which annunciate the flight path and show the intended path, the aircraft position and any deviations;

- flight controls, which control the aircraft to the desired flight path;

- Honeywell's SmartView, which provides a synthetic vision picture of the desired flight path and any nearby terrain.

Cundiff notes that Honeywell is a designated FAA RNP consultant and helps operators get approved for RNP Operations through its Go Direct Services. The company also provides the required database monitoring service to RNP operators, he adds.