2 Avionics template 18.qxp_YearBook Template 27/07/2017 09:35 Page 30
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For the US, Specifically…
Aside from 1090ES transponders, Universal Access Transmitter (UAT) versions may also be deployed for ADS-B Out, operating at a lower 978 MHz frequency. This version is popular with General Aviation light aircraft, especially if they do not need to fly in Class A airspace or internationally, where 1090ES is always required. Essentially, UAT services are only provided below 18,000 feet and only available in the US. Having 978 UAT also allows ‘ADS-B In FIS-B’, a no cost traffic and flight information service. This FIS-B service is provided in addition to TIS-B, available to all with ADS-B In. Traffic Information Services – Broadcast (TIS-B): a transitional technology that provides aircraft, equipped with ADS-B Out and utilizing ADS-B In capability, with client-based surveillance information. This relates to aircraft that are not ADS-B equipped and over the next three years should be less of a need. To qualify as a TIS-B target, an aircraft must be equipped with a transponder and be within radar coverage.
strapped specifically into each aircraft. If an aircraft changes its registration, a new Mode S address must be added as a maintenance action item. ELS also provides the aircraft’s altitude information in 25ft increments. ELS has further evolved into Enhanced Surveillance (EHS), by adding more data elements to the transponder transmission, using Downlink Aircraft Parameters (DAP) services. These data elements consist of: Magnetic heading Indicated airspeed or Mach number Vertical rate Roll rate Track angle rate True track angle Ground speed Selected altitude. Integration with existing AHRS and Air Data systems is required for some of these data elements while for older aircraft, additional wiring may be required. Also, if aircraft are TCAS II equipped they will have full Mode S capability. For ADS-B Out using transponders operating at 1090 MHz, the EHS version becomes Extended Squitter, or 1090ES.
Flight Information Services – Broadcast (FIS-B): provides meteorological and aeronautical data to the cockpit. This service is not client-based and is always broadcast on the 978 MHz UAT frequency. FIS-B is not available on the 1090 MHz frequency (1090ES). Owners and operators of most jet and turboprop aircraft must determine if they have 1090ES version transponders that are integrated to other aircraft systems for the additional ADSB data required. It is further essential to make sure that Mode S strapping is current for the ICAO address, specifically assigned to your aircraft registration. Another available client-based service is Automatic Dependent Surveillance - Rebroadcast (ADS-R), which relays ADS-B information transmitted by an aircraft broadcasting on one link (for example UAT) to other aircraft equipped with ADSB In operating on a different link (for example 1090ES), and vice-versa. Ground stations convert and relay the respective frequency data matching the aircraft receiving frequency. Aircraft utilizing ADS-R will have a ‘hockey puck’ shaped area created around them, for sharing the ADS-B information with other aircraft within the same area but not on the same datalink (frequency).
Aircraft Position Information
ADS-B not only relies on the communication provided via the Transponders but also on the aircraft’s position, available from the onboard Global Positioning Systems (GPS). The existing