[n86121]

Well, ...the 9900BX interrogates 1090 transponders around you, then tracks all the targets. It sees the superset of any and all 1090 transponder equipped aircraft, independently and directly. Its internal software then calls out 'threats.'

For ADS-B to pass you a non-ads-b target, first, ground radar has to see the other guy, and then you have to be within sight of an ADS-B ground station for the other target to be sent up to you.

I fly in the Outerbanks NC periodically, and frankly there are a lot of holes in that theory.

ADS-B WILL pass you another ads-b out equipped aircraft real-time. In that mode it is the logical end-state for transponders that makes a lot more sense than prior tech.

BUT...

True, in theory, by Jan 1 2020 most aircraft are supposed to have ads-b. But interestingly enough, that's impossible. Not enough avionics shops out there to refit the fleet.

Airlines have been given an extension, as the cost in downtime and benefit, especially if already equipped with TCAS, are negligible.

So FAA will face reality check: If aircraft not equipped by ADS-B are not allowed into terminal areas, or anywhere ads-B is required, then GA will stay out, significantly reducing the utility and value of those aircraft, as they can only be flow in the countryside, and never to any city or controlled airspace.

I really like the 9900BX (X means w interrogator) because it sees the superset. You can buy BX units on ebay for about $3500, so if you are already wired up and ready to plug in, that might be a consideration!