Technically, you do not need radios. There are many many uncontrolled airports in the United States, where you can technically fly around without establishing two-way radio communication. It’s doable, but I don’t know if that’s even a scenario pilots test in the simulator during their semiannual trainings.

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tjohns 6 hours ago | parent [-]

Most air traffic is IFR. You definitely need radio for IFR traffic in for deconfliction in most of the world. (There's a few exceptions in very remote places, but that's mostly academic.) Even legacy procedural (non-radar) separation assumes you have working radio, and a radio failure is an emergency.

VFR traffic doesn't necessarily need radio, and is not affected by this groundstop.

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bombcar 5 hours ago | parent | next [-]

You don’t need radio for IFR (as the whole point of a flight plan is that if you lose contact you continue to fly your plan). But you kind of do need radar.

	▲	tjohns 4 hours ago \| parent [-]
		You actually don't need radar, and ATC can do non-radar "procedural" control where they block off sections of airways or entire airports, one-in one-out at a time, like sections of railroad track. There are still a few parts of the remote US, as well as large sections of Northern Canada, where radar coverage is nonexistant and ATC is done via procedural control. Radar outages also happen on occasion, which would necessitate this. As for lack of radio, this would only work if ATC blocked out your entire route from start to finish - which isn't practically ever done. Otherwise, they need to be able to maintain positive control over your flight since the airspace isn't reserved, which means conflicts are possible. If you lose radio communication, it's an emergency and they'll move everyone out of your way. This doesn't work very well if everyone loses radio communication simultaneously.

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valleyer 5 hours ago | parent | prev [-]

Right, but isn't a lot of that necessary radio aircraft-to-aircraft, like ADS-B? Obviously not ideal, but I thought IFR traffic could feasibly maintain separation without ATC help.

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tjohns 4 hours ago | parent [-]

ADS-B can't legally be used to maintain separation. It's only approved for use as an aid to awareness for additional safety.

Could you in an emergency, if you had no other options? Yes. But ATC can't legally give you a clearance that was dependent on using ADS-B for separation.

(Similarly, if there's a potential traffic conflict, and you tell ATC you see the other traffic on your ADS-B display, they just have to disregard that statement and assume that you can't see the other aircraft at all.)

	▲	valleyer 4 hours ago \| parent [-]
		Interesting, thanks.