Air Traffic Control

Applications
Title	Air Traffic Control
Edited by	GMV
Level	Intermediate
Year of Publication	2011

Air traffic controllers need position, heading, speed and time information for the continuous management of all aircraft. Some areas of the world lack the appropriate ground infrastructure, including secondary radar and communication links. Standardized transmission of GNSS navigation data will lead to advanced systems and techniques for safer air traffic monitoring.

The Automatic dependent surveillance-broadcast (ADS-B) is currently the most important system used in Air traffic controllers (ATC) side, which relies on GNSS as primary data source, to obtain aircraft's horizontal positions.

Application Architecture

The ADS-B is part of Next Generation Air Transportation System systems and uses GNSS as primary horizontal position data source for the provision of an acceptable accuracy and integrity performance in support of the ATC separation services contained within the ADS-B application.

Airborne Surveillance Systems (ADS-B)

This description was partially adapted from the ADS-B definition at Skybrary.

The ADS-B is an aircraft's mean to automatically transmit and/or receive traffic information to/from other aircraft and to air traffic control. This information includes the aircraft identification, position, altitude, speed, and other parameters, which are determined by equipment such as GNSS receiver and barometric encoder, and will aid the air traffic controllers to keep the aircraft safely separated in the air and on the ground, as well.

Once it becomes fully implemented, the ADS-B aviation technology will bring a major improvement in terms of surveillance, enhancing the ground radar based surveillance systems.

The ADS-B goal is to provide a real time complete picture of traffic for both pilots and air traffic controllers, which can facilitate the separation management, reducing costs and improving safety.

Throughout ADS-B the aircraft, aerodrome vehicles and other objects can automatically transmit and/or receive data such as identification, position and additional data as appropriate in a broadcast mode via a data-link. The transmission of identification and position data will move air traffic control from a radar-based system to a GNSS-based aircraft location system.

The ADS-B broadcasts the ownship on-board position information automatically in a defined frequency of 2Hz, without any knowledge about who is listening to the information and without being able to receive any request calls. However, the ADS-B is dependent of the on-board position sources and on-board broadcast transmission systems.

On the aircraft side, the flight crews will then use ADS–B In information to adjust their airspeed or flight paths to maintain the instructed separation.

The position sourced by GNSS tightly integrated with inertial navigation systems will be obtained from systems such as:

• GPS L1 and L5
• Galileo
• Glonass
• SBAS (EGNOS, WAAS, GAGAN, MSAS)

These applications are considered safety critical applications.

The biggest risk associated with provision of GNSS is the potential for denial of service by deliberate jamming, and consequently backup mechanisms are required.

Surface Movements

Surface operations include navigation on the airport surface to and from the active runway. These operations are currently conducted visually. However, the use of GNSS will enable the ability for aircraft movement without visual references in the Next Generation Air Transportation System (NextGen). With more accurate information, ATC will be able to position and separate aircraft with improved precision and timing.

Application Characterization

The main benefits coming from the adoption of ADS-B are the following:

• Accuracy of GNSS positions is better and more consistent, than position accuracy provided by ground radar systems.
• The installation of ADS-B systems is cheaper than the installation of ground radar systems and can easily provide gains in a airspace that doesn't own radar systems.
• The broadcast mechanism of ADS-B, provides a traffic awareness mean for both ATC and nearby aircraft.

The GNSS combined with Cockpit Display of Traffic Information (CDTI) technology improves the situational awareness on an airport. The introduction of a moving map display including presentation of surrounding traffic enabled by ADS-B In/Out will significantly reduce runway and taxiway incursions. By providing the pilot with conflict free routing, together with target times, the system will considerably improve taxiway throughput and reduce taxiway delays.

In the ATC side, the ADS–B transmission signals from aircraft will be fused with surveillance data from both primary and secondary radars before being displayed. The controllers, therefore, are receiving and viewing a composite of aircraft data from multiple surveillance systems.

The ADS–B surveillance data will improve the performance of ATC decision support tools, which rely on surveillance data to make predictions.

The necessary equipment on the aircraft side to support the ADS-B system is a GNSS receiver capable to do the necessary calculation of integrity and accuracy and a datalink transponder to broadcast the ADS-B data. The ADS-B Out capability, that reports to ATC and other traffic nearby, is the only one which will be obligatory.

The aircraft ADS-B In is the equipment which encompasses the datalink receiver and listens to the information provided by other aircraft, providing the information usually onto a GNSS map in a CDTI. This information is often integrated with Traffic Collision Avoidance System (TCAS), however in General Aviation applications the ADS-B receiver is a standalone receiver.

The ADS-Contract (ADS-C) is another ADS application, which is meant to be used in flights above areas without radar coverage. This application sends reports periodically to the nearest ATC.

Application Examples

The following companies are among the major manufactures of ADS-B equipments for Commercial Aviation (CA):

• Honeywell (US)
• Rockwell Collins (US)
• Thales Avionics (FR)

The following companies are among the major manufactures of ADS-B equipments for General Aviation (GA):

• Garmin (US)
• Honeywell (US)