Future Flight: Communications Revolution

Part 11 of 12

Today we live in a wired, wireless world. Just look around. Everywhere you go people have cell phones glued to their ears on a more or less permanent basis. More cell phone towers are being built to accommodate the proliferation of cell phones. Many of us have Internet access at home, work, and through our cell phones. Satellite television services give us access to hundreds of channels. Soon, satellites will beam hundreds of stations' worth of radio programming to our cars—meaning that we could drive across the nation unencumbered by line-of-sight and signal-range problems, and listen to the same radio frequency. There's a lot of electronic chatter going on, and it will only increase in the years to come. That goes for aviation, too.

Frequency congestion and 8.33 kilohertz spacing

With the across-the-board increase in air traffic we've seen in recent years, our existing pool of allocated VHF communications frequencies is rapidly loading up. On some ATC frequencies it often seems that you can hardly get a word in edgewise. The growth in air traffic has already prompted two jumps in the communications frequency spectrum—from 180 to 360 channels, and from 360- to 720-channel frequency spacing—and now we can expect more splitting of the aviation communications band.

The VHF spectrum currently allocated to aviation communications runs from 118.000 to 135.975 megahertz. Notice that there are three numerals after the decimal point. A new initiative would give us four numerals after the decimal point, and 2,280 more badly needed channels. These additional channels would come about by dicing up the comm spectrum into 8.33-kilohertz slices. It's a proven technique that's already being used to reduce delays in Europe, where airline traffic has exploded in volume over the past 10 years.

Now the United States must deal with the same problem, using the same method. This means a vast overhaul of ATC and aircraft hardware in the next few years. Translation: Unless you already have a brand-new comm radio (the newest radios are already equipped with this feature, to make them competitive in the European market), you'll have to buy one with 8.33-kHz spacing in about six years or so. Of course, so will ATC. The inevitable delays in implementing a project of this magnitude suggest that the timetable for making the switch to the new spacing probably won't happen until sometime after 2005.

To ease the transition, it's very likely that the new frequencies will be phased in gradually, say, with usage initially limited to the high-altitude airspace structure. But there'll be nothing to ease the economic burden of gearing up your panel to play the expanding-decimal game of the future.

VDLs 3 and 4

There's an alternative to the 8.33-kHz expansion. Some advocate the use of digital communications, using VHF datalink (VDL) frequencies 3 and 4, saying the demand for additional communications and other uplinked functionality can't be served any other way. By 2009, proponents say, we may well be using VDL 3 and 4 for voice, uplinked weather information, and ADS-B (automatic dependent surveillance-broadcast) and other traffic advisories. These VDL frequencies would be squeezed into the one-kHz segment between 136.00 and 137.00 MHz.

VDL uses what experts call time differential multiple access (TDMA) technology. Under this scheme, the pilot with a VDL 3 radio makes a radio call—or gets a textual clearance change from ATC—from a ground-based transceiver. The radio traffic works both ways in a request-reply arrangement. VDL 4 adds ADS-B or TIS traffic information, weather graphics, and other information in its uplink capabilities; it was mentioned briefly in an earlier installment of "Future Flight" (see " Links to Tomorrow," February Pilot). The difference between VDL 3 and VDL 4 is that VDL 3 "listens" for one of four time slots to open within each of 20 channels spaced 20 kHz apart, then sends or receives its transmissions when an opportunity avails itself. It doesn't take long, however, with transmissions able to come and go at almost instantaneous speed. VDL 4 doesn't need to operate under this scheduling scheme—its messaging is self-organizing, depends on airborne equipment to process messages, and can operate independently of ground-based equipment.

Though its implementation could take more than a decade, those in the know say that a VDL-capable radio ought to cost the approximate equivalent of $5,000 in today's dollars. The good news about VDL 3 and 4? They should serve aviation's communications needs for a 30-year period, and their use will probably be limited to the high-altitude airspace structure, where it would primarily serve airliners.

What about VDL 2?

It's understandable if you've gone acronym-happy by now. The happiest of you are probably wondering: Hey, he mentioned VDL 3 and 4. What happened to VDL 1 and 2?

VDL 1 and VDL 2 are alive and well these days, serving as the vehicle for transmitting digital ACARS (airborne communications addressing and reporting system) messages. ACARS is used by the airlines and larger corporate jets to forward messages. The airlines, for example, use ACARS to learn of gate changes, and transmit passenger, maintenance, and other information between their dispatchers and aircraft. VDL 2 is also being used in an experimental program aimed at streamlining ATC workload. Known as CPDLC (controller-pilot datalink communications), the idea is to free controllers to use their time focusing on sequencing and separation of traffic.

One study found that 40 percent of a controller's workload consisted of such routine—yet time-consuming—tasks as establishing initial radio contact with air traffic or handing traffic off to another frequency. With CPDLC these contacts are uplinked to the cockpit in text format using VDL 2.

In spite of the glitz surrounding VDL, so much progress has been made in the 8.33-kHz area that it will likely become the method of choice. The 8.33-kHz option promises more frequencies, much sooner than VDL. And with the threat of imminent "frequency gridlock," 8.33-kHz spacing appears a simpler, more attractive choice.

No speed demons

The promise of datalink transmissions immediately raises the question: What's the fastest that text messages, weather graphics, e-mails, and faxes can travel across the sky? The answer, according to current projections, is a discouraging 9,600-baud speed—in other words, the kind of terrestrial modem speeds that were cutting edge several years ago. True now, but we'll see much higherspeed access within two years.

A phone in every cockpit?

Of course, 8.33-kHz spacing or VDL communications won't be the only way we communicate from the cockpits of the future. Airborne telephony—once the province of the very few, and which required a cumbersome operating procedure—is here to stay. Like everybody else, pilots have grown accustomed to the convenience and utility of wireless telephones. Now a whole new industry has sprung up to meet a rising demand for a new generation of cockpit telephones.

Airborne telephones work via one of two methods: cellular and satellite. The first, cellular communications, mimics the technology used by terrestrially based cell phones. After engineers developed strategies that prevented airborne cell phone transmissions from interfering with terrestrial cell phones (changing the polarity of the signals and keeping the signal strength down), the Federal Communications Commission approved the first of what will surely be a wave of airborne cell phones.

AirCell Inc. now offers its AT.01 cell phone system for $3,995. This includes the phone itself, a transceiver, and a low-profile antenna. AirCell's $7,400 AGT.01 cell phone system comes with two transceivers—one for use in airborne communications, the other for use on the ground—making this a dual-purpose telephone. In either application, the methodology is the same: Pilots and passengers make calls by first contacting terrestrial cell phone antennas; then the transmission is shunted along to the recipient via land lines and/or other cell phone transmission antennas. Faxes, e-mails, connection with the Internet, and uplinking of weather graphics and text information can all be performed using the AirCell network. Today's maximum baud rate of the AirCell system—like every other current airborne phone system—is 9,600 baud. However, AirCell expects to see high-speed modems in use within two years.

AirCell uses a network of some 100 antennas across the United States to make its system work. The entire nation has yet to be covered, but more antenna sites are being activated. Because the antenna transmissions operate on a line-of-sight basis, coverage usually begins at approximately 5,000 feet agl; in mountainous regions, where terrain-induced signal interference is a major issue, the altitudes at which coverage begins can be even higher. Cell-to-cell handoff switching is automatic, so coverage is uninterrupted as you fly; there's no voice delay; and premium features such as call waiting, call forwarding, and conference calling are also available. The basic monthly fee is now $29.95, and calling rates start at $1.75 per minute. For more information, visit the Web site ( www.aircell.com).

AirCell recently teamed with Garmin to provide cell phone service for Garmin's NavTalk Pilot—a combination cell phone and GPS receiver. The NavTalk Pilot sells for $2,990, making this phone less expensive than AirCell's. The same communications features as AirCell's, however, are available in tiered service levels. A neat feature of the NavTalk Pilot lets you call the nearest air route traffic control center by holding down the "9" key. Using the NavTalk Pilot, weather graphics can be uplinked, interfaced, and displayed on Garmin's popular 430 and 530 panel-mount GPS/VHF nav/com units. For further details, visit the Web site ( www.garmin.com).

One of the first low-cost satellite phones has just been introduced by Icarus Instruments Inc. ( www.icarusinstruments.com). Called the SatTalk II system, it uses a Qualcomm 1600 handset and the Globalstar constellation of 48 communications satellites in low earth orbit. The caller's signals go to a satellite first, then are relayed to the recipient via land lines. Like the AirCell AGT.01, the phone can be used to make calls in the air and on the ground. The advantage over cellular is that satellites provide better coverage from their lofty perches, and don't impose line-of-sight problems. SatTalk coverage currently includes all of North America (except northern Alaska), southern Europe, the Caribbean, the northern half of South America, and parts of Africa, Asia, and Australia. Further coverage expansion is on the way. In addition, ground stations to be built in Newfoundland, Iceland, and England will provide coverage over the North Atlantic.

The SatTalk telephone goes for $1,195, and is available from any Globalstar dealer (see www.globalstar-usa.com). The audio controller, antenna, cables, and other hardware costs another $3,995. Monthly service plans range from $20 and up, and per-minute charges are $1.75 and lower, depending on the service plan you choose.

Other satellite communications (satcom, for short) packages are available, but their prices ($40,000 to $235,000), weights, and complex installations make them prohibitive for all but the larger corporate jets. Their baud rates aren't any faster than those of the equipment packages we've mentioned above, most are analog systems (like those described earlier), and in some cases they're as slow as 2,400 baud. Their chief advantage, however, is worldwide coverage.

These telephone systems can be fitted out to work with your headset. Once telephone contact has been made, you key the microphone to make your voice transmission; incoming transmissions are fed directly to the headphones. In the SatTalk and NavTalk setups, any ATC transmissions will automatically suppress incoming telephone signals. SatTalk even plays a recorded "please stand by" message to the person you're conversing with when you are busy talking with ATC; after you release the microphone switch, you're back on the phone.

Here to stay

Airborne telephones aren't flash-in-the-pan gimmicks. They provide an alternate means of communications should you have an electrical, radio, or audio panel malfunction; allow you to conduct business when the situation permits; and let you receive important weather and other messages while you're flying. Though their manufacturers emphasize that you can remove most of these telephones from the cockpit and use them as you would a terrestrial telephone, it's a safe bet that most will stay in the cockpit and become yet another staple in the growing amount of communications and display gear. A few short years ago they would be considered exotic novelties. Those days are over. These days, more communications capability—be it derived from more frequencies, VDL, or telephony—is rapidly becoming standard.

Links to more information on communications technology may be found on AOPA Online ( www.aopa.org/pilot/links/links0011.shtml ). E-mail the author at [email protected] .