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Computerworld - Today's commercial airliners come packed with computers smart enough to land the planes, but when it comes to air-ground communications, much of the airline industry uses voice radio systems that haven't changed much since the era of propeller-driven DC3s.

Vital communications about weather or route changes between pilots and company dispatch centers, as well as air traffic controllers, run over narrow-band and often overcrowded voice radio circuits that resemble an old-fashioned party-line telephone.

When pilots can transmit on one of these VHF air-ground circuits, the poor quality of the connections and ambient noise often require them to repeat themselves. Even with repeats, these voice communications are prone to errors.

Some airlines do use air-to-ground data communications systems, but current technology provides a connection with a data rate equal to that of an early-1980s dial-up modem, 2.4Kbit/sec. Although it provides clearer and more error-free communications, this slow data service doesn't support advanced needs such as automatic updates of avionics software. The VHF radio channels that support this data service are also becoming crowded and harder to access.

Communications companies that serve the airline industry, such as Arinc Inc. in Annapolis, Md., and Societe Internationale de Telecommunications Aeronautiques (SITA) in Geneva, have developed a new data service called VHF Digital Link Mode 2 (VDLM2), which more than quadruples the air-ground data rate while using relatively uncrowded portions of the VHF aviation radio band.

But major airlines, still cash-strapped in the wake of 9/11, have been slow to adopt this new service fleetwide. One exception is low-fare pioneer Southwest Airlines Co. in Dallas. Southwest plans to equip its 388 planes with VDLM2 by the end of this year and will deploy the technology on half of them by this summer, according to Brian Gleason, the carrier's director of flight operations, technical.

Brian Gleason of Southwest Airlines Co. Image Credit: Phil Hollenbeck

When Southwest started operations in 1988, it served just three Texas cities with a handful of planes. At that time, it built its own network of ground stations operating in the upper end of the 108/137-MHz VHF aviation band, which allowed pilots to place calls to the company's dispatch center using a touch-tone keypad. Even though Southwest expanded the network of ground stations, it still could accommodate only one voice call at a time, frustrating pilots who needed to contact the dispatch center for weather updates or route changes.

To break that logjam, Southwest in January reached an agreement under which Arinc will provide the airline with VDLM2 service over an Arinc-owned network of 148 VHF ground stations that cover North America, says Gleason. Southwest first considered using the Aircraft Communications Addressing and Reporting System data service that Arinc introduced in the 1980s, but it passed because of the service's low bandwidth and congestion in the ACARS frequency band, which runs from 129.125 to 131.475 MHz.