The Coming Digital Radio Mandate

The FAA has begun flight testing a new digital communications system that it calls Nexcom, for "next-generation communications." The modernized system will eventually require that the entire U.S. GA fleet, from Airbuses to Zlins, be equipped with new digital radios.

The mandate for change in the panel will be accompanied by a complete revamping of the ground communications network. This program, called FAA Telecommunications Infrastructure (FTI), will replace the current ad-hoc system-some sites are FAA owned; others are leased (from multiple vendors)-with one that will be more integrated, more reliable, more flexible and more capable, as well as more efficient and less costly to maintain and administer than today's system. The modernization program won't be cheap, however. The contract, which the FAA last year awarded to prime contractor Harris Corporation, will cost $1.7 billion over the next 15 years.

The FAA says that Nexcom is overdue, and it's hard to argue otherwise. For more than 50 years, pilots flying in the United States have seen little change to the technology behind the faceplates of their radios. Our current VHF communications system was introduced back in the 1940s, and on only a couple of occasions has the FAA made substantial modifications, in both cases by carving up the frequency pie into smaller slices. The last big change, which the FAA adopted in 1972, doubled the number of frequencies by the reduction from 50 kHz to the current 25 kHz-channel spacing, creating 760 channels, 524 of which are used in the National Airspace System (NAS). Since that time the need for additional frequencies has grown at a steady rate, averaging just less than four percent a year over that period. Today there are more than 10,600 ATC frequencies, and the FAA deems that by around 2010 it will become impossible to provide enough frequencies in certain areas even with "extraordinary spectrum re-engineering."

Several years ago, European aviation authorities, when faced with a similar challenge, chose to create more channels by implementing 8.33 kHz spacing, which creates three channels on each of the existing 25 kHz slices. The new spacing plan resulted in more frequencies but with greater interference from neighboring channels and with the same technology limitations as the current system, including low voice quality and channel blockage (stuck mic) issues. Moreover, 8.33 spacing is probably the tightest that the current technology can bear without unacceptable levels of interference.

The Digital Solution Instead of going the 8.33-spacing route, the FAA has decided to go digital. In addition to more frequencies, four for every 25 kHz slot on the dial, digital air-to-ground (A/G) will offer lower upkeep costs, enable datalink, reduce frequency interference, improve system security (a hot selling point these days) and permit more flexibility in channel assignment. At first, the system would be mandated for flights in Class A airspace (generally speaking, the airspace above 18,000 feet) in the United States, soon thereafter being adopted for approach and terminal areas. Utilizing VHF digital link mode three, or VDL-3, the system will allow for both long-distance voice (up to 200 miles) and datalink, though the FAA has yet to decide on how it will split the spectrum between voice and data channels. The datalink capability will be used for relaying messages between controllers and pilots, which the FAA thinks will become the norm for most communications with commercial air traffic over the long haul.

Programs that require airplane owners to buy and install new equipment (known as mandatory equipage) are generally greeted with trepidation by Beltway member organizations. But in this case, Skyhawk drivers need not panic, at least not for a while. The Nexcom system will be a multi-mode-both analog and digital-one, so when the system is implemented, pilots flying below 18,000 feet will still be able to make their calls using the same old 720-channel radios that are in the panel right now. At some point, the FAA will likely require everybody to equip with digital radios, but the agency hasn't yet announced the details or timeframe for the change, which, barring any major programs shifts, won't come before 2010. In the meantime, our old radios will continue to function, for better or for worse, as they always have.

The new radios will sound better and have less interference. Otherwise, the differences between old and new-tech equipment will be transparent to pilots, who will simply enter frequencies pretty much as they always have. There will be enhanced services, such as datalink and, possibly, the FAA's datalink weather service, called flight information services, or FIS. Also, Nexcom will allow for something called "frequency nomination," which will let the controller send the next frequency up to the pilot, who will then simply hit the flip-flop switch.

First Digital Radios on Their Way When Europe first set out on the 8.33 kHz spacing journey, its adoption of the standard was delayed for years because there were no radios commercially available. To avoid this fate for Nexcom, the FAA has awarded pre-implementation contracts to three radio manufacturers, Avidyne, Collins and Honeywell, to develop digital radios to fit the coming mandate.

Progress has been right on track. Last summer the FAA conducted a successful flight test of Avidyne's digital radio as installed in an FAA 727 testbed aircraft. During the flight test over Atlantic City, the radio demonstrated all the digital voice and data modes (VDL-3) with the FAA's prototype ground station at its Atlantic City test center. The tests, says Avidyne, were an unqualified success.

Collins and Honeywell are developing digital radios for the air transport market, and Avidyne is working on a model for light aircraft, from piston singles up through cabin-class twins and light jets.

Avidyne expects to certify its as-yet-unnamed digital radio in 2004. It will, at first, sell the radios to airplane manufacturers, but it plans to offer retrofit versions soon thereafter. The radio, which will be a standard panel-mount affair, will cost around $5,000, slightly more than existing technology navcom radios. Avidyne expects to work the new radio technology into its Entegra flat-panel avionics suite, allowing it to eliminate the need for separate radios and to "greatly enhance" the capabilities of the airplane's avionics, especially in terms of flight planning and ease of flying instrument approaches.

The notice of proposed rulemaking covering Nexcom is expected soon, and the FAA anticipates a final rule by the middle of 2005. Implementation isn't scheduled until 2009, and that date, says the FAA, looks likely to slip soon by a year or more.