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.