The Aeronautical Telecommunications Network (ATN) is a major player in the resolution of the current perceived dilemma and is working with ICAO to help in bringing about the "Free Flight" concept. Being a driver of a four-wheel drive vehicle, I am often tempted to follow unoccupied and sometimes undeveloped roads to avoid the delays caused by saturation of the public highways. What if an aircraft could takeoff and would be free to fly the most direct route to the destination — all without the delays associated with following the published and heavily traveled routes?
Also, suppose that all the while, the flight crew were free from the burden of having to tune communication radios and stay in constant contact with an Air Traffic Controller. Instead, any message of significance would be transmitted to the aircraft using a digital format and the crew would have readable displays strategically located in the flight deck. Areas of high density traffic would no longer require extensive assigned frequencies.
In many commercial/business aircraft, radio tuning can be accomplished by the Flight Management Systems (FMS) and they, like the Radio Transmitters and Radio Tuning Units (See sidebar "Dividing VHF"), will require in most cases, a software change to be 8.33 kHz- certified. Any aircraft that is non-compliant will have to either be re-routed or will have altitude restrictions imposed when flying in 8.33 kHz-approved airspace. It is anticipated that this will meet the need for the next five years, however most in the business realize ongoing increases in the number of channels is not the ultimate solution. Currently, there is no mandate in the United States to require the 8.33 kHz change. The answer will most probably be the introduction of Data Links otherwise known as Digital VHF Transmissions.
Definition of compliance has already been realized for the flight deck of an ATN-equipped aircraft. The most noticeable difference will be the installation of Data Communication Display Units (DCDU). In addition, an "ATC Message" annunciator will occupy a prominent place. All radio communication systems including VHF, HF and even Satellite will be connected into a Data Router. It is this device that will determine the most effective downlink with the ground and will alleviate the crew’s having to make the selection of communication mode or frequency selection.
The obvious advantages here are not without cost. It is anticipated that outfitting one aircraft to this level could cost as much as US $500,000. To accommodate this new technology, several International agreements will have to be adopted. These will include the specifications for a universal digital data link, consistency in worldwide Air Traffic Control systems, and reduced political barriers.
Implementing Free Flight
Some modernization of the Air Traffic System is taking place in both North America and Europe, which will hopefully lead to realization of the Free Flight concept. In the US, the FAA has implemented a two-phase program. The first initiative that began in 1998, provides Air Traffic Controllers with the ability to manage user requests for specific airspace. This system employs a method to identify inappropriate convergence between aircraft and provide up to a 20-minute advanced warning, enabling controllers to create specific arrival sequence tactics. Incorporation of a Final Approach Spacing Tool (FAST) will help make the most of runway use. In fact, the FAA currently is evaluating an Automatic Dependent Surveillance-Broadcast (ADS-B). This is a proposed method that enables pilots to unmistakably locate other air traffic in their airspace and negotiate themselves in an orderly and safe fashion to the ultimate destination. A Surface Movement Advisor (SMA) is another concept that can supply airlines and other flight operations with aircraft present position information to allow better synchronization with ground support. This initiative is planned to be completed by the end of 2002.
Once the first phase of the plan is complete, "Free Flight - Phase 2" is scheduled to start. This phase will concentrate on expanding good methods and tactics and eliminating practices that are not effective.
Key to the future
It certainly appears that the digital data link is the key to the successful future of the Air Traffic Control system. Voice communications between air and ground will have to be drastically modified to avoid restricting future growth. The need for a worldwide seamless Air Traffic Management system is well realized. Despite the fact that there are few who oppose this concept, implementation has been a slow process.
A look at analog and digital communications.
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