Air Transport World

Building a digital bridge: high-speed digital ATC communication arrives in a form that brings many dividends to the airline industry. (Avionics).(air traffic control)

High-speed controller-pilot data link communications, launched in its first-ever daily use in early October, opens a new era of aviation communications that solves ATC radio frequency congestion while giving airlines a much bigger digital pipeline to their own cockpits.

The initial daily use of VHF Data Link Mode 2 at FAA's Miami ATC Center was 13 years in the making and, if the Build 1 implementation is sufficiently successful, will lead to a coast-to-coast Build 1A system in the next few years, perhaps as early as December 2005. In addition, Eurocontrol, also fighting the frequency congestion monster, is leaning toward the ICAO-developed VDL2 as well.

And while competing data link modes on the horizon raise the possibility that VDL2 will not be the long-term choice for ATC messaging, there is no doubt that it will remain with the industry for many years as the digital ACARS replacement.

To be clear, airlines for years have been using data link for ATC messages. The FANS system uses ACARS-based messaging via satellite and HF radio to talk with long-haul aircraft, usually those on transoceanic routes out of range of land-based VHF stations. This link also is used to relay the aircraft's GPS-derived position back to the ATC service provider to produce automatic dependent surveillance. However, the technology involved with FANS is slow, expensive when satellites are used and not sufficiently secure for use in high-density domestic airspace.

Over land, airlines have been using ACARS to get airport terminal condition reports and, before pushback, route clearances.

Meanwhile, available ATC frequencies have been gobbled up as service providers try to keep controller workload to manageable levels by increasingly segmenting the airspace, each segment requiring a new frequency. With the provider unable to create new segments, traffic more easily overloads a controller and backs up, creating costly delays.

The first approach to the problem was a series of cuts in the gap between channels, halving the initial 100kHz spread to 50kHz, then halving it again to 25kHz as technology permitted closer spacing without interference.

In Europe, with major hubs relatively close together--increasing the opportunity for interference between facilities--and densely populated with aircraft, the frequency congestion crunch hit earlier than in the US. …

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