Why would an owner decide to put in an ADS-B UAT transceiver versus an ADS-B ES transceiver? What are the advantages and disadvantages of both systems?

  • $\begingroup$ Do you mean 'transceiver'? Or perhaps transmitter? $\endgroup$ – egid Jul 3 '16 at 5:46

ADS-B UAT operates on 978 MHz and are available for aircraft that operate below 18,000 FT MSL. UAT transceivers can display aviation weather products (FIS-B) as well as traffic from ground radio stations (TIS-B). The airplane must be in a coverage area for TIS-B services.

TIS-B is intended to provide ADS-B equipped aircraft with a more complete traffic picture in situations where not all nearby aircraft are equipped with ADS-B Out. - AIM 4-5-8

Aviation weather products available over FIS-B through ADS-B UAT transceivers Aviation Weather Services provided by FIS-B

ADS-B 1090ES operates on 1090 MHz and is required for aircraft operating above 18,000 FT MSL. The information sent over a Mode S transponder is greater and is called an "extended squitter". These aircraft will be able to display traffic directly from other ADS-B equipped aircraft and those with Mode S transponders without the need to rely on ground based systems. FIS-B is not available to these transceivers.

The picture below illustrates where 1090ES and UAT are allowed / required for aircraft after the ADS-B mandate in 2020.

ADS-B required coverage area



Even though it’s called a “Universal Access” transceiver, the 978 MHz UAT is actually less universal that the 1090 MHz “ES” transponder in terms of where it can fly and what airspace it can use.

The FAA will require 1090 ES transponders for aircraft operating higher than 18,000 ft MSL — while UAT is limited to aircraft that will operate no higher than 17,999 ft MSL

Source: Garmin

So, ES takes you higher. But UAT carries free weather information for the ADS-B In option.

Extended Squitter carries more data, it can even one day show the controller what you intend to do, like for example your programmed route, and VNAV performance.

  • $\begingroup$ How does TIS-B and FIS-B fit into this technology? $\endgroup$ – wbeard52 Jul 4 '16 at 0:39
  • $\begingroup$ 1090ES data does not include your programmed route and VNAV performance. $\endgroup$ – DeltaLima Jul 4 '16 at 7:34
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    $\begingroup$ @ymb1 I prefer to check EUROCAE ED102A/ RTCA DO-260B, the EASA CS-ACNS and FAA AC 20-165B in favour of sales documents. In version 1 of 1090ES ADS-B messages were foreseen to transmit route information, but they were not mandatory to be implemented. In fact it was never implemented for various reasons. In version 2, these messages have been withdrawn from the protocol. I am expecting a new form of route information to be included in version 3, but that is work in progress and will not be implemented before the ADS-B mandate date of 2020. $\endgroup$ – DeltaLima Jul 4 '16 at 11:48
  • $\begingroup$ FIS-B is only available to aircraft with UAT 978 MHz transceivers. AC 90-114A Appendix 5. $\endgroup$ – wbeard52 Jul 5 '16 at 2:16
  • $\begingroup$ Why did you rollback the answer? I thought it was better with more information. $\endgroup$ – wbeard52 Jul 7 '16 at 14:47

If the aircraft will be flown above 18,000ft or in other countries with an ADS-B mandate, 1090ES is required. This applies to pretty much all "large" aircraft; they have no choice.

However, the US has an enormous light GA fleet with very vocal owners, and the FAA itself was concerned about 1090MHz congestion, so they added UAT (on 978MHz) as an alternative. It was assumed this would be simpler and less expensive than replacing every transponder in the entire GA fleet (which seems to be true), and they also added free weather (FIS-B) to encourage GA owners to choose UAT unless they actually need 1090ES, in case the price difference wasn't enough.

Note that both options offer TIS-B/ADS-R.


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