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What is ADS-B?

Get your ADS-B questions answered here regarding the 2020 mandate.

ADS-B or Automatic Dependent Surveillance – Broadcast, is a system for air traffic surveillance. With ADS-B, each aircraft broadcasts its own GPS position along with other information like heading, ground track, ground speed, altitude. Receivers on the ground then receive this information and send it to air traffic control displays. The ADS-B information can be used to augment existing primary and secondary (transponder-based) radar or used in lieu of those radar technologies. Aircraft that broadcast this information are considered to be equipped with ADS-B Out.

The information broadcast by each aircraft can also be received by other nearby aircraft and that information can be displayed on a traffic display such as a multi-function display (MFD). Aircraft that can receive ADS-B information have ADS-B In.

The ADS-B information used by air traffic controllers will allow improved separation services along with additional future applications such as continuous descent approaches. ADS-B information in the cockpit will allow better situational awareness and traffic avoidance along with future applications such as self-separation.

Ground vehicles on airports will also be equipped with at least ADS-B Out to help prevent runway incursions.

ADS-B Out systems automatically broadcast an aircraft’s (or ground vehicle’s) GPS position about every second. ADS-B In systems receive those broadcasts from other air and ground vehicles along with from FAA ground stations. The ground station data can include other traffic information along with weather and NOTAM information. The data received with an ADS-B In system is dependent on the ADS-B link and the capabilities of the receiver. Some ADS-B systems do both ADS-B In and Out.

The FAA has mandated ADS-B Out by 2020 on all aircraft operating in current Mode-C airspace (Around class B and C airspace along with above 10,000 ft). The mandate allows either 1090-ES or UAT ADS-B Out on aircraft. The 1090-ES link is required for aircraft that fly above FL180.

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The FAA and their contractor, ITT, are on track to have the entire ADS-B ground infrastructure in place by 2013, 7 years before the mandate. This ground infrastructure is already available for most of the East coast and supports TIS-B, ADS-R, and FIS-B along with sending ADS-B information to ATC.

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European mandate for ADS-B OUT requires 1090ES ADS-B Out with a Diversity Mode-S transponder by 1/8/15 for new aircraft and 12/7/17 for retrofits, and only applies to aircraft >12,500lbs or max cruise >250kts TAS.

Click to download the Commission Implementing Regulation Documentation.

The FAA mandate supports two technologies for ADS-B, 1090 MHz Extended Squitter (1090-ES) and Universal Access Transceiver (UAT). 1090-ES uses the same frequency used by Mode-S transponders and includes the ADS-B information as extra data on the Mode-S transponder transmissions, hence the ‘extended squitter’ name. UAT uses the 978 MHz frequency that has been reserved for ADS-B. Since there is a difference in frequencies between the two technologies, UAT receivers cannot receive 1090-ES ADS-B transmissions and 1090-ES receivers cannot receive UAT transmissions.

The ADS-B ground stations will re-transmit the information on the opposite link so that all aircraft can be seen on cockpit traffic displays. This is known as ADS-R, R for rebroadcast.

The UAT technology also allows additional information to be uplinked to aircraft from ground stations through FIS-B (Flight Information System – Broadcast). This information includes weather and TFR information similar to the information already provided by XM or Sirius/WSI.

FIS-B stands for Flight Information System – Broadcast and is only available with UAT link ADS-B In. When in range of a ground station, weather and NOTAM information can be received by a UAT receiver and displayed in the cockpit on a MFD or EFB. The following data is currently available: AIRMETs, SIGMETs, METARs, NEXRAD, NOTAMs, TFRs, PIREPs, SUA Status, TAFs, and Winds/Temps Aloft. This data is similar to information already provided by XM or Sirius/WSI, however the update rate is faster with FIS-B, but the geographical coverage area is much smaller. For example at low altitudes, only 150nm of NEXRAD is available and 250nm of METAR, TAF, and AIRMET data. Additionally at remote airports, no data may be available on the surface.

TIS-B stands for Traffic Information System – Broadcast and involves ADS-B ground stations sending Secondary Surveillance Radar (SSR) targets to aircraft with ADS-B In. TIS-B targets will be updated at least every 2 seconds on the surface, 6 seconds in the terminal area, and 12.1 seconds in the en-route airspace.

ADS-R stands for Automatic Dependent Surveillance – Re-broadcast and involves ADS-B ground stations repeating ADS-B messages from one link (1090-ES or UAT) to the other link for aircraft with ADS-B In. ADS-R targets will be updated at least every 2 seconds on the surface, 5 seconds in the terminal area, and 10 seconds in the en-route airspace.

TAS systems, which must meet TSO-C147, are on-board, active-surveillance Traffic Advisory Systems that independently interrogate nearby transponder-equipped aircraft and determine bearing and range from the replies.

ADS-B is dependent upon aircraft broadcasting their GPS positions to other aircraft. To see other aircraft, they must be broadcasting ADS-B Out messages and you must be equipped with ADS-B In to receive those messages. ADS-B is dependent on other aircraft having being equipped to support ADS-B Out.

There are two types of TCAS (Traffic Collision Avoidance System), TCAS I and TCAS II. TAS systems are almost identical to TSO-C118 TCAS I systems, in fact they use the same set of requirements or Minimum Operational Performance Standards (MOPS). Both systems actively interrogate nearby Mode A, C, and S transponders and issue Traffic Alerts (TAs – “Traffic, Traffic”). The difference is that TCAS I systems have a 1030 MHz receiver that can detect the number of nearby TCAS systems and thus send a more powerful interrogation when fewer aircraft are nearby. TCAS II systems go beyond TCAS I systems in that they require dual Mode-S transponders, they can coordinate with other Mode-S transponders on other aircraft and they can issue Resolution Advisories (RAs – “Climb, Climb”).

Active Traffic Systems (including TAS and TCAS) use Mode-A, C, or S transponder interrogations to determine aircraft bearing and distance. Altitude is determined by reported Mode-C altitude. After the ADS-B mandate, aircraft will still be required to have a Mode-C or S transponder in airspace where it is currently required, thus Active Traffic Systems will continue to function.

Active Traffic Systems are valuable for three reasons in an ADS-B environment. First, during the initial equipage period (through 2020) not all aircraft will have ADS-B. Thus without an Active Traffic System, those unequipped aircraft would not be displayed on a cockpit traffic display even if you had ADS-B In. Second, since the FAA mandate allows both 1090-ES and UAT ADS-B technologies, if the ADS-R system is not functional or you are out of range of a ground station, the ADS-B In will not display aircraft of the opposite type. An Active Traffic System will display all aircraft independent of the type of ADS-B Out since all aircraft will still be required to have a Mode-C or Mode-S transponder. Third, ADS-B is dependent on GPS signals, so during periods of poor satellite geometry or solar storms, GPS position and thus ADS-B will not be available. The FAA is keeping ATC radars as a backup and an Active Traffic System can act as a backup to ADS-B in the cockpit.

Yes. Avidyne is going to offer SkyTrax600A, TAS610A, and TAS620A traffic systems. Availability and pricing has not been announced yet. See ../products/tas-a/index.html for more information.

ADS-B In support in the TAS will allow the TAS to receive ADS-B information from 1090-ES equipped ADS-B Out aircraft. It will still also display traffic information from Mode-A, C, and S transponders. The range for receiving ADS-B information is larger than can be used for active traffic interrogations, increasing the effective range of the TAS for ADS-B In. The ADS-B position will also be used to enhance the accuracy of the bearing and range to a target.

The TAS also will receive the additional information provided by ADS-B (heading, track, on-ground status, etc) and provide this information to compatible traffic displays. The MFD or other display must be updated to take advantage of this additional information.

No, you must equip with an ADS-B Out system to be compliant with the FAA ADS-B mandate.

First if you have an Avidyne TAS system, Avidyne recommends signing up for the SkyTrax600A upgrade now to lock in the price and in order to get ADS-B In benefits as soon as possible. With respect to ADS-B Out, there are two major reasons for waiting to equip. First, as of this post, there are no products currently on the market which meet the FAA’s mandate for TSO-C166b (1090-ES) or TSO-C154c (UAT). These TSOs are based on RTCA MOPS that were not published until late 2009, and thus no existing ADS-B manufacturers have created compliant systems. Second, as more manufacturers enter the market, the prices of ADS-B systems are expected to drop significantly. Just as panel mounted GPS systems evolved rapidly in the first 10 years of being on the market, with increasing features at reduced prices, similar trends are to be expected with ADS-B systems before 2020.

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