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.
