ADSB OUT
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If ADSB-OUT has a unique ID, why do you have to set your transponder to a specific code?

Don Nelson
3 Replies
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Because the ancient ATC systems aren't yet wired to work off just ADS-B identifiers, especially 978 UAT data.  I'd give it another 20 years (and universal ADS-B-out equipage) before transponders go the way of 4-course ranges.  Heck -- we've still got NDB's and ADF's, and when I started flying in 1969, those were going to be gone before the 20th century ended.
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Ron, you're showing your age talking about A-N ranges :); I suppose I am too! Just a few weeks ago I was reading a part 135 regulation that addressed runways being marked by flare pots and lanterns! In a current version of part 135.229! When was the last time any one of us used those? 

I just wanted to add this for the OP - in addition to the ads-b required use regulations under 91.225, the transponder required use regulations under 91.215 are still in play as well; they have not been changed nor rescinded with the advent of ads-b..
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Donald, the ATC actually *can* work just fine off of only ADS-B data. However, in airspace where there is both ADS-B and secondary surveillance radar coverage, squawking the same code (your ADS-B Out picks it up automatically from the transponder, whether 1090ES or 978UAT) makes it much easier for the FAA's ATC software to correlate the transponder and ADS-B targets. Otherwise, one aircraft might be mistakenly displayed as two. Some pilots experienced this in the early days of ADS-B In, when their own aircraft showed up as a (disconcertingly close) target on their traffic display.