Simplifying ADSB

TexasGyro | 26 August, 2015 08:27

Automatic - having the capability of starting, operating, moving, etc., independently.
Dependent - relying on someone or something else for aid, support, etc.
Surveillance - continuous observation of an activity in order to gather information.
Broadcast - to transmit programs or signals.

ADSB is commonly referred to in two different manners: ADSB IN and ADSB OUT. Only ADSB OUT is required by the FAA and there are two different ways to achieve OUT.

Extended Squitter
Since the first transponder was installed for general aviation use decades ago, the ATC system has been based on a 1090 Mhz frequency standard. It doesn’t matter if you are flying a 172 with a KT-76A, or a Canadair with an MST-67A, they both provide the same basic information to ATC using 1090 Mhz. The information needed to make ADSB work wouldn’t fit in the standard Mode S framework, so the addition of the Extended Squitter was required. Extended squitter, or ES, adds the ability to transmit considerably more data than before, to include latitude/longitude, vertical rate and heading. This lets the system know where you are and what you are doing. Extended squitter is required for operations above 18,000’, or operations at any flight level outside of the US in countries requiring ADSB. Bendix King and Garmin both offer direct replacement transponders that include ES capability. You must have a WAAS capable GPS onboard and some wiring changes are necessary in order to make it work. Extended Squitter transponders are NOT capable of providing ADSB IN.

978 Mhz UAT (Universal Access Transceiver)
For those of us operating below 18,000’ we have the option of installing a UAT. UATs are considerably more labor intensive to install, but can provide ADSB IN capability. As with the ES option, the UAT requires a WAAS capable GPS input. Many manufacturers now provide UAT models with built in WAAS receivers for the customers who do not want the added expense of a GTN-750 (or similar). The UAT provides both traffic and subscription free weather information to compatible displays

SO...

If you operate above 18,000’ and don’t want ADSB IN then all you need is an Extended Squitter transponder and WAAS GPS.
If you operate above 18,000’ and want ADSB IN then you will need an Extended Squitter transponder, a 978 UAT, and a WAAS GPS.
If you operate below 18,000’ you have your choice of either an ES Transponder or a 978 UAT, combined with a WAAS GPS.

The 18,000’ requirement is based on where you operate, not where your aircraft is rated to go. In theory you could install a 978 UAT in a Falcon 50 and as long as you didn’t exceed 17,999’ then you would be legal.