August 1, 2006
In the early days of U.S. space programs, skeptics doubted the practical value of any new discoveries. Apart from granulated orange juice and better wristwatches, they said, what possible benefits could the public derive from all those expensive satellite launches? Today we're finding out. In spades. One of the biggest benefits is datalink communications. And general aviation stands to be one of the biggest beneficiaries.
As usual, military and space applications were the first to make extensive use of datalink technology. Back in August 1977, NASA launched Voyager 2, the second of two deep-space probes designed to investigate magnetic fields, cosmic rays, and other charged particles in the outer reaches of the solar system. NASA received data — as well as televised imagery of Uranus and Neptune — via datalink over the 8415-MHz frequency. NASA also can transmit commands to the spacecraft via datalink. That's quite a testimony to datalink's power to exchange vast amounts of valuable information. The surprising thing is that Voyager continues to send and receive datalink transmissions, even though it passed Neptune in 1989, and passed out of the solar system last year.
Datalink works by sending and receiving packets of digitized signals. As in the case of the Voyagers, aviation signals are relayed to and from Earth stations via Earth-orbit satellites.
The first general aviation applications of datalink technology began with the in-flight two-way messaging offered by companies offering flight-planning and handling services to large business jets flying long routes. This messaging comes via VHF datalink, and is called the Aircraft Communications Addressing and Reporting System, or ACARS for short. Simply speaking, ACARS is e-mail between the cockpit and the flight department or flight-planning service provider. Then came in-flight telephones and Internet connections using satellite-based signal relays.
What those two services delivered were the convenience, speed, and safety of near-instantaneous communications concerning not just the status of the flight (for example, a change in an overflight permit's terms, or new arrangements at the destination airport), but also the communications needs of the passengers.
Now datalink is for all of general aviation. Even the smallest piston singles can make use of datalink weather services, which beam the latest radar images and other graphical and textual weather information directly to your panel-mount multifunction display — or to portable electronic devices. These include electronic flight bags, personal digital assistants, and even cell phone displays.
Datalink also is capable of providing traffic information. Via the new automatic dependent surveillance-broadcast (ADS-B) technology, airborne transceivers exchange position, speed, altitude, and track information with each other — and with the FAA's system of air traffic control radars (see " Automatic Dependent Surveillance Broadcast [ADS-B]," page 90). The result: better traffic data in areas poorly covered by ATC radars, and much better traffic awareness in ADS-B-equipped aircraft. The concept has been successfully tested, and looks to be a promising next step in the air traffic control system and methodology of the future — a future in which pilots and controllers can share the same traffic information.
Datalink may well play a major part in the way ATC communicates clearances and advisories. Text messaging is already available in some private-sector datalink messaging service packages and in some locations ATC uses text messaging to issue clearances to pilots.
Skeptics may worry about the bandwidth needed for this wide-ranging datalink of the future. But if Voyager can still send data from beyond the solar system, then the technology must surely exist to accommodate a rapidly growing number of users.— Thomas A. Horne, Editor at Large
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