Approach

Applications
Title	Approach
Author(s)	GMV.
Level	Medium
Year of Publication	2011

Approach, landing and take-off are critical flight phases and the major need of commercial operators is to have full operations in all weather conditions. As a consequence, precision approach is a mandatory requirement.

The GNSS, with the aid of ground-based augmentation (local elements), will satisfy the needs for precision approach as defined in the aeronautical standards, and could replace or complement the navigation infrastructure of airports in regions where the system is inadequate. The most prominent example is the airports that not equipped with instrument landing systems.

Application Architecture

For approach and landing, the Instrument Landing Systems (ILS) will remain the primary source of guidance for CAT I/II/III operations in major airports, because is the current standard system for precision approach.

Approach systems are commonly designated as precision or non-precision and it worth's to distinguish between those systems:

These descriptions were adapted from the Operational Requirements For a Global Navigation Satellite System for ICAO.

Precision approach systems: A precision aid is designed to guide aircraft, by the use of azimuth and glide path information, along a defined runway approach path to a decision height (DH) ranging from 200 feet to 0 feet above the point of touchdown.

Non-precision approach systems: A non-precision aid is designed to bring the aircraft sufficiently close to an airfield to allow the pilot to have a clear view of the runway to enable the aircraft to be landed without recourse to any other navigation aid. A non-precision approach may use a variety of systems to fix position, and in some cases uses the information provided from the en-route system or from systems whose guidance signals do not give position fixes accurate enough for precision approach and landing.

With the introduction of a GNSS system, it may be possible for this single system to satisfy the operational requirements for both precision and non-precision approaches without the need for any other ground based navigation system situated within the vicinity of the final approach fix or at the airfield.

The performance-based service-oriented operational concept will driven the modification of the approach systems Concept of Operations. As GNSS landing is progressively introduced, ILS will revert to a backup system to support the risk of GNSS outage.

Performance-based approach

The Performance-based navigation approach method is used because it puts available a number of advantages, over the sensor-specific method, offering to operators a new instrument approach facility at a significantly lower cost than existing ground based alternatives.

Unlike traditional sensor-based approach procedures like VOR or ILS, that require a specific sensor complement to fly an approach, RNAV approach procedures provide a common information for pilots.

In addition, the moving or modification of a VOR station will originate an impact on several procedures, as VOR can be used on routes, VOR approaches, missed approaches, etc.

Using GNSS, the need to maintain approaching routes based in ground sensors will be reduced minimizing the associated costs, for instance, in terms of fuel.

Adding new sensor-specific procedures will intensify the cost, and the rapid growth in available navigation systems would soon make sensor-specific routes and procedures unaffordable.

Finally, ILS is not an option available in all airports. In certain airport scenarios there is no ILS, due to the lack of terrain available around the runway, e.g., airports located in river banks, or near sea shore.

The Receiver Autonomous Integrity Monitoring (RAIM) limit for non-precision approach is 0.3 NM.

Application Characterization

The approach and landing systems will increasingly move to GNSS based landing in order to improve airport accessibility, either in CAT I conditions (ILS and GNSS as backup/complementary systems) or CAT II/III conditions (GBAS CAT II/III with ILS/MLS backup).

Aircraft's will increasingly rely on GNSS to fly steep, curved and segmented approaches in the terminal area, to improve capacity and reduce environmental impact.

For LVP (Low Visibility Procedures) operations, lighting presents more than 50% of the investment cost. As more airports are able to handle these types of operation, lower cost lighting technologies will be developed and made available.

The GNSS aviation approach applications will be supported by an augmentation system. In order to use SBAS for approaches, Air Navigation Service Providers must publish runway procedures and aircraft and operators have to be equipped with certified receivers and be approved for operations.

GBAS

The GBAS provide GNSS integrity monitoring through data obtained from the ground. They also increase the accuracy of satellite navigation, clearing the way for GNSS precision approach and landing. A ground station at the airport transmits locally-relevant corrections, integrity data and approach data to aircraft in the terminal area in the VHF band. GBAS, or ground-based augmentation systems, will increasingly support CAT II/III operations where economically beneficial once enhanced GNSS become available. It is assumed that all GBAS for CAT I stations will be upgraded to CATII/III stations.

WAAS

The WAAS system implemented in USA improves the accuracy, reliability and integrity of the GPS signal. GPS-WAAS navigators that meet Federal Aviation Administration (FAA) WAAS regulations may be used for sole means of navigation for all phases of flight, including precision approach at airports.

The Wide Area Augmentation System offers an opportunity for airports to gain Instrument Landing System (ILS) approach capability without the purchase or installation of any ground-based navigation equipment at the airport.

The WAAS vertically guided approach procedures are considered LPV (Localizer Performance with Vertical guidance) and provide ILS (Instrument Landing System) equivalent approach minimums as low as 200 feet at qualifying airports. Actual minimums are based on an airport’s current infrastructure, as well as an evaluation of any existing obstructions.

EGNOS

EGONOS is a satellite-based augmentation system that improves the accuracy of satellite navigation signals over Europe. The signals are guaranteed to the extremely high reliability set out by the International Civil Aviation Organisation standard.

EGNOS offers the aviation industry the means to provide accurate and safe vertically guided approaches to smaller airports and its introduction will reduce delays, diversions and cancellations of flights into and out of these airfields while improving passenger safety.

The EGNOS Safety-of-Life signal was recently formally declared available to aviation. For the first time, space-based navigation signals augmented by this system have become officially usable for the critical task of vertically guiding aircraft during landing approaches.

Application Examples

Garmin owns several products, such as for example:

• GTN750,
• GTN725,
• GTN650,
• GTN635,
• GTN625,
• GNS 530W,
• GPS 500W,
• GNS 430W,
• GNC 420W or
• GPS 400W.

These devices have WAAS navigation capabilities and are approved to fly LPV glideslope approaches without reference to ground-based navaids of any kind.

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.