Datalink is said to be the "next big thing" in general aviation avionics, but getting it into the cockpit depends on manufacturers and users finding a compelling justification - the "killer application". The cockpit display of traffic information has been viewed as one possible early application, but some believe graphical weather could bring the breakthrough.

Adoption of datalink has been hampered by delays in key decisions, in the USA and internationally, on which links to use for which sectors of the aviation market. While the US Federal Aviation Administration's flight information service - broadcast (FIS-B) is using VHF datalink Mode 2 to uplink textual and graphical weather to GA aircraft, its companion traffic information system - broadcast (TIS-B) initially uses the Mode S link prevalent in air transport.

Meanwhile, the FAA is about to promulgate its decision on the datalink choice for automatic dependent surveillance - broadcast (ADS-B). It is expected to select 1090MHz Mode S extended squitter (1090ES) for the air transport sector, and the lower-cost 966MHz universal access transceiver (UAT) for general aviation. UAT transceivers built by UPS Aviation Technologies are flying in Alaska under the FAA's Capstone operational evaluation, which involves ADS-B, FIS-B and TIS-B.

While 1090ES is suitable for ADS-B and TIS-B, it does not have the bandwidth required for graphical weather. UAT has sufficient capacity, and promises to be affordable. But minimum operating performance standards - required for certification - have only just been approved in the USA.

At the same time, the number of satellite datalinks available for graphical weather delivery is proliferating. Echo Flight, and now Avidyne, use the Orbcomm low-Earth orbit (LEO) satellite constellation. This allows use of a low-cost VHF datalink and standard whip antenna, but offers a relatively low data rate. Iridium and Globalstar, other LEOs capable of broadcasting weather, use L-band and S-band, respectively. The latest weather broadcast services to emerge, Satellink Technologies' Merlin and WSI's Pilot Weather Advisor, use L-band links provided by geostationary communications satellites.

Source: Flight International