En Route Navigation
|Title||En Route Navigation|
|Year of Publication||2011|
GNSS overcomes many of the deficiencies in today’s air traffic infrastructure thanks to its accurate, continuous, all-weather positioning. During en-route flight, the availability of GNSS will ensure high robustness through the redundancy and high reliability of the service. 
In the future, higher accuracy and service integrity will allow aircraft separation to be reduced in congested airspace, to cope with traffic growth and airspace infringement. GNSS will be used in en-route flight phase of commercial aircraft.
Currently the aviation industry faces meaningful challenges to overcome the services increasing across the world. Safety solutions are a demand in all flight phases in order to cope with traffic capacity, all-weather conditions and efficiency.
In terms of en route navigation systems, the conventional ground-based navigation aids (e.g., VOR, NDB, ILS), limit the routes and procedures to their physical locations. Although these safety ground based systems are being used in the aviation industry, as well as the Visual Navigation procedures, they lack the flexibility of point-to-point operations.
In the future, GNSS is foreseen to become the main source of positioning data for en route and terminal area operations.
Currently, GNSS information is already used in en route and Terminal Control Area Positioning, in order to determine the Horizontal position of the aircraft. 
The GNSS information will be obtained from global navigation system and augmentation systems such as:
- GPS L1 and L5
- SBAS (EGNOS, WAAS, GAGAN, MSAS)
On the other hand, GNSS information is not used in en-route and Terminal Control Area(TCA) Trajectory Management.
These applications are considered safety critical applications.
The en route phase is comprised from completion of initial climb through cruise altitude and completion of controlled descent to the initial approach fix. The navigation systems used in en route phase shall be operational compatible with approach and landing systems.
The navigation applications on specific routes or within a specific airspace must be defined in a clear and concise manner. This is to ensure that the flight crew and the air traffic controllers (ATCs) are aware of the on-board Area Navigation (RNAV) system capabilities in order to determine if the performance of the RNAV system is appropriate. 
The RNAV can be defined as a method of navigation that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of a self contained system capability, or a combination of these.  Improved operational efficiency derived from the application of area navigation (RNAV) techniques has resulted in the development of navigation applications.
ICAO has developed a framework for defining navigation performance requirements. This method is called performance-based navigation (PBN) and it consists in the specification of performance requirements.
The Performance-based navigation (PBN) concept specifies that aircraft RNAV system performance requirements shall be defined in terms of the accuracy, integrity, availability, continuity and functionality, which are needed for the proposed operations in the context of a particular airspace concept. Performance requirements are identified in navigation specifications, which also identify the choice of navigation sensors and equipment that may be used to meet the performance requirements. These navigation specifications are defined at a sufficient level of detail to facilitate global harmonization by providing specific implementation guidance for States and operators.
PBN describe the technologies that allow aircraft to fly flexible, accurate, three dimensional flight paths using on board equipment and capabilities. PBN frees aircraft from reliance on fixed, ground-based radio-navigation aids and creates economic, environmental, safety and access benefits.
In PBN method there are two important concepts:
- Area Navigation (RNAV): The already mentioned RNAV, is a form of Performance Based Navigation in which equipment onboard the aircraft calculates and follows a direct navigation path between two points, without the aircraft having to overfly intermediate, ground-based navigation aids.
- Required Navigation Performance: The RNP is a type of Performance Based Navigation that allows an aircraft to fly a specific path between two 3-dimensionally defined points in space. RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board performance monitoring and alerting in RNP.
For en-route operations, the transition to GNSS cannot be isolated from the progressive introduction of the PBN concept which comprises both RNAV and RNP specifications that defines the capabilities required for an aircraft to navigate in a particular airspace segment as well as the navigation infrastructure.
The expansion of satellite navigation services is expected to contribute to the continued diversity of RNAV systems in different aircraft.
The PNB goal is mainly to gradually switch to global area navigation by means of implementing navigation specifications. This transition will occur from conventional navigation to area navigation (RNAV) and from local/regional RNAV to performance-based navigation.
The global harmonization intents to reduce the number of operational approvals required by air operators and to enable airlines to operate seamlessly from country to country.
There are several ways to ensure integrity. The integrity service of ICAO compliant GNSS systems may currently be provided by the three normalized augmentation systems known under the terms ABAS (Airborne Based Augmentation System), GBAS (Ground Based Augmentation System) and SBAS (Satellite Based Augmentation System).
In addition to integrity service, GBAS and SBAS also provide differential corrections to improve the precision in a restricted area around a single reference station for GBAS and over a wide area defined by a network of reference stations for SBAS. 
Characteristics of GNSS en route applications
Aviation equipment characteristics vary considerably from handheld portable devices to a flight deck mounted fully integrated system.
In commercial aircraft, the equipment is permanently installed in tested and approved locations with appropriate power supplies, and is fully integrated with other flight systems.
Aviation pilots are increasingly using GNSS equipments in order to improve aid to safe navigation.
Most of those equipments are sold with aviation databases and are certified for use in IFR flight. Usually the equipments feature a moving map display, and most of the devices have features to warn the pilot in case of approaching airspace reservations. Some equipment offers vertical navigation guidance, including minimum safe altitude identification.
Some devices, especially that used by general aviation, are portable with battery power and lightweight antenna design. These devices require ground training and they could create more problems in use rather than aid safe navigation when used by pilots who do not fully understand its limitations and its capabilities.
Among many other companies in the market, there are also the following manufacturers:
- Approach Systems
- Any Where Map
- Lowrance - AirMap 600C This is a mapping handheld GPS device.
- AvMap - EKP IV This is a portable navigation system.
- ^ GSA GNSS Market Report - Issue 1, October 2010.
- ^ Galileo Application Sheet - Aviation Applications, ESA and European Commission, October 2002
- ^ SESAR Consortium, The ATM Target Concept D3, September 2007
- ^ ENR in Skybrary
- ^ a b c d e Performance-based navigation Manual, ICAO, March 2007
- ^ Area Navigation Systems in Skybrary
- ^ Required navigation performance in Wikipedia
- ^ The SBAS Integrity Concept Standardised by ICAO. Application to EGNOS, EGNOS navigation conference publications, 2001