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Comment by code4tee | Hacker News Reader

Radar isn’t going away. This article talks as if ADS-B is replacing radar, which it’s not. It’s enhancing radar where radar coverage exists and providing coverage on traffic where radar coverage currently does not exist (usually lower altitudes away from major airports and over the ocean).

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Indeed. Not everyone even has to have ADS-B Out. You only need it if you’re going into or over Class C or B airspace, in the Class B veils, Class E above 10,000 except below 2500 AGL, and in Class E over the Gulf of Mexico. That leaves huge swathes of airspace—dare I say most airspace in the US—where ADS-B isn’t required. You could fly across the entire country without hitting an ADS-B requirement. And the only way for ATC to see non-ADS-B aircraft is radar.

Except that is also the same airspace where ATC doesn't have to see you. You don't even need a transponder to fly in those areas.

It’s not just about seeing you, it’s about seeing everyone around you too. ATC’s job is to separate aircraft and they can’t do that if they can’t see non-ADS-B aircraft. In fact just today I overheard an approach controller vector an American Airlines jet around VFR traffic at 1700’. That VFR traffic was in “non-rule” airspace, where ADS-B isn’t required. (I saw the jet and the VFR traffic from my cockpit.) They won’t be able to do that without radar.

I was under the impression that one of the main drivers of ADS-B is to enable smaller separation between aircraft due to the more accurate position reporting. If that's the case, then radar won't be a useful backup because planes would be closer than the radar can separate them.

Planes under IFR will be as close as ATC policies want to run them. If everything's working and separation standards become 2nm laterally, then when there's a GPS or ADS-B outage, we can just revert to the 5nm separation standards and use radar backup.

That might be easier said than done, though, because there may not be enough space to do that. If you have the airspace packed at 2nm and then you need to revert to 5nm, all the planes will fill 2.5x as much area. Plus, how would ATC safely effect that separation when the planes are closer than resolution of the equipment.

ADS-B and Mode A/C/S (MSSR) are both secondary radar. but the equipment differs, in particular the ground equipment looks different. It could be that the MSSR equipment gets phased out as ADS-B prevails. Primary radar will continue to be used though, in particular at airports (ones other than the many local uncontrolled variety).

Oh, good. I can't read the article (paywall) but was hoping they weren't actually replacing radar with GPS. Using GPS to enhance radar seems a lot better.

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