ADS-B out is available on the 1090 (Mode S) band, and can even be implemented as a firmware update to some Mode S transponders.
In the case of 978 ADS-B Out, I believe that it is still necessary to keep operating a Mode C transponder for operations where Mode C is currently required, as noted in This video at 16:25, in order to work with TCAS systems. Continuing on to 41:24, there is a recommendation stating that if a Mode C transponder fails, it should be replaced with an ADS-B "out" transponder. Here are my questions:
- Is there such thing as a 978 transponder which will meet ads-b out requirements and eliminate the need for Mode C, or does this recommendation essentially mean that you move to a 1090ES transponder?
- Perhaps this recommendation is assuming that there was no ads-b out at the time. Given an aircraft with a failed mode-c transponder, what equipment options which meet the mandates are worth considering for GA aircraft? Apparently John Zimmerman does not recommend Mode C + 978 out. It appears he recommends 1090ES. Either one of these would seem to benefit from having 978 in. I can see no advantage to 1090ES in, as it appears to offer only a subset of the 978 services, unless it was desired to be able to receive 1090ES air-to-air or our operate outside the US.