Air Traffic Control Moves to GNSS

By on 13 May, 2010

About ten years ago it became clear that in many parts of the world airspace was approaching saturation point. Air transportation was plagued by delays, and safety had begun to be compromised. The existing outmoded groundbased radar systems, already stretched to the limit, were hardly able to cope.

In the US, there are around 50,000 flights every 24 hours. It is predicted that by 2025, the daily figure will increase to 150,000.

In Europe, similarly, as aviation continues to grow, the existing equipment will begin to falter. European airspace has to accommodate more than 33,000 flights on busy days. An added complexity is the fact that around 70 per cent of flights in the EU cross national borders.

Authorities around the world came to realise that a new generation of air traffic management systems ? one capable of ensuring the safety and efficiency of air travel over coming decades ? was essential.

Accordingly, the US Federal Aviation Administration (FAA) has launched a plan to create 30 per cent more capacity in its national airspace system by 2013.

The result is the Next Generation Air Transportation System, or NextGen, now undergoing development and testing in the US.

The EU counterpart is the Single European Sky ATM Research program or SESAR.

Both NextGen and SESAR involve a transition from a ground-based system of air traffic control to a satellite-based system.

One of the main features of the new systems is that pilots will be, to some extent, their own air traffic controllers.

NextGen will comprise three main elements: surveillance (tracking an aircraft's position), navigation and communication. Each aircraft will be equipped with a GPS transponder. It will continually exchange data with air traffic control on the ground, and with all other aircraft in the vicinity.

Each pilot will see what?s going on in real time on a screen in the cockpit display, pretty much as the air traffic controller on the ground does. This is expected to greatly enhance safety and efficiency, and also lead to significant fuel savings.

The backbone of NextGen is the Automatic Dependent Surveillance-Broadcast (ADS-B) technology. It uses GPS and ground-based equipment to transmit precise aircraft location information (ADS-B Out) to air traffic controllers and other aircraft, and to receive precise location information about other aircraft (ADS-B In).

ADS-B will provide information of far greater frequency and accuracy than the current land-based radar systems. This is partly because the horizontal position accuracy of the system does not depend on the distance between the aircraft and the ground station. With radar, the further away an antenna, the less accurate the computed position.

The ADS-B system provides accuracy of about 25 metres for an airborne GPS receiver and about five metres for a DGPS. With secondary radar, the azimuth accuracy is inferior to 0.08 degrees and the distance accuracy is less than 70 metres.

The system in the aircraft converts the position acquired from GPS signals into a digital code. It combines it with other data from the aircraft?s flight monitoring system ? including the flight number; ICAO aircraft 24 bit address (a globally unique airframe code); position, latitude/longitude, and position, integrity/accuracy; and barometric and geometric altitudes. It also adds rate of climb/descent, track angle and ground speed, and emergency indication data.

Every second, the aircraft?s transponder automatically broadcasts the code with all the data. ADS-B-equipped aircraft will receive the broadcast, as will ADS-B ground stations up to 300 kilometres away.

Australia is one of several countries that have already decided to adopt ADS-B. The Australian Advanced Air Traffic System, or TAAATS, has been upgraded to process 1000 ADS-B flights simultaneously from up to 200 ground stations. It will use the technology to provide controllers with automated safety-alerting capabilities and continuously monitors the assigned route and altitude of ADS-B-approved aircraft.

In the first stage of Australian implementation, in December 2013, ADS-B Out units will be mandatory for aircraft operating above 29,000ft (in other words, for all scheduled commercial jetliners). Australian recreational aviation will probably also be required to fit this equipment for operators in controlled airspace, but that is unlikely to happen before 2020.

ADS-B will also help enhance the safety of operations on the ground at airports. It will support systems such as Airport Surface Detection Equipment. This system will obtain information from various sources, including ADS-B and radar. It will allow controllers to visually track all traffic on the airport surface. It is already in use in 12 US airports, and by the end of this year will be installed in all the country?s busiest aerodromes.

The FAA has also developed procedures to improve the safety and efficiency of navigation. Another software product, Tailored Arrivals, allows controllers to tailor an aircraft?s flight path to weather and traffic conditions, starting when they are about 300 kilometres from the airport. The software has already been tested and has delivered significant fuel savings.

Under a Tailored Arrivals approach, aircraft make smoother descents, which is far more fuel-efficient. Currently, pilots are forced to use their engines to correct their flight path during their descent. The new practice eliminates the need to do this.

Another new innovation concerns communications. Currently, 17 different voice switches are deployed within US air traffic control facilities, each with its own limitations. NextGen will use a universal NAS voice switch to improve communication between flight crews and controllers. It will also streamline voice communications with more reliable digital technology. Data communications will take over many tasks which now use voice communications.

In 2003, US Congress created the Joint Planning and Development Office to implement NextGen. Partners in the JPDO include NASA, the National Oceanic and Atmospheric Administration, the White House Office of Science and Technology Policy, and the US departments of Defense and Homeland Security.

Europe's 'single European sky' vision is part of an in-depth reform of the air traffic management organisation and performance within the union. It aims to eliminate the present fragmented approach and ensure global interoperability. About 70 companies from 18 countries across Europe are participating.

The SESAR development phase (2008-13) will produce the new generation of technology, components and operational procedures. Large-scale production and implementation of the new infrastructure will occur between 2013-20.

As our skies become more crowded, authorities face increasing responsibility to keep air passengers and crews safe. NextGen will be part of the answer.

Paul Grad is an engineering writer living in Sydney.


Issue 46; April – May 2010



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