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I read 5,000 to 10,000 aircraft are flying at a given time. There are several very unexpected but plausible reasons to land all planes quickly, e.g: a war / terrorism event; a giant volcano eruption); or a major meteorite impact

Whatever, in case there is a sudden need to stop flying, what would happen:

  • From an ATC standpoint, is there any impossibility to conduct such massive landing?
  • Is there enough runway throughput to allow planes to land quickly?
  • Is there enough room to park all aircraft?

Is there any preparation for this kind of operation in some countries?

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    $\begingroup$ You could read about the last time this happened: The Day the FAA Stopped the World. $\endgroup$ – Greg Hewgill Sep 25 '17 at 22:01
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    $\begingroup$ What is "quickly" or "at once" mean? Can aircraft be put in a holding pattern and given an hour to get on the ground? Does it have to be in 10 minutes? $\endgroup$ – Ron Beyer Sep 25 '17 at 22:15
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    $\begingroup$ The scenario here is somewhat misleading. There's no single organization that would have to land all the planes, since they're spread all over the world. $\endgroup$ – David Richerby Sep 25 '17 at 23:57
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    $\begingroup$ @GregHewgill I guess "The Day the FAA Stopped the USA and Canada Stopped Itself" isn't such a catchy title. Is Time aware that there's actually quite a lot of world outside the USA? You know, the place where all those international flights come from. $\endgroup$ – David Richerby Sep 26 '17 at 0:07
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    $\begingroup$ @GregHewgill During 9/11 the priority was not to get all planes on the ground as soon as possible, though – many incoming planes were turned away from the USA, and diverted (mostly to Canada) or flew back to their origin. So, while related, I think the premise of the current question is somewhat different. $\endgroup$ – Fab Sep 26 '17 at 0:17
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Assuming that GA/small private and commercial aircraft land at separate locations:

Say that around 80%, of those airplanes are GA flights (which they probably are); you would have around 6000 GA airplane flights based on your average number of 7500. Based on that number, it would be theoretically possible to stack quite a few landings concurrently à la Oshkosh. Given that three runways there can land and park somewhere around 8000 airplanes in a couple days (from 6am to 8pm), I would say that spreading that many planes out across all the airports in the world, you could ground almost all GA aircraft within an hour or so.

Note that this kind of operation requires a bit of set up and coordination, so it would probably take a longer to actually pull this operation off.

Commercial aircraft would take a bit longer though as a good number of them would be flying at cruise altitude from which it takes ~30 minutes to comfortably get down from. However, some of these aircraft would be in an over-water flight which would take maybe 4 hours to even reach a decent airport, after which it would have to get into the pattern which might toss on another hour or so to that.

Under the best conditions, I would say that to clear the skies would take around 4.5 hours, but it could probably take longer than that due to airplane concentration in certain areas and some people messing up their landings.

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    $\begingroup$ Flight Aware at the moment (6:15 UTC): "Tracking 8,323 airborne aircraft", I don't think 80% are GA, so your base of 1,500 commercial aircraft is probably low. $\endgroup$ – mins Sep 26 '17 at 6:18
  • $\begingroup$ Yes, I've been wondering what the number of planes including general aviation is. The number of 10k aircraft airborne seems to be passenger jets. I don't think GA is 80% of what's in the air, certainly not outside the US. A passenger jet is in the air maybe a fifth to two thirds of the time, 2000 to 5000 hours a year. Most GA planes fly only hundreds of hours per year. So, even if the GA fleet is larger than the jet fleet, they're not in the air that much, and as such constitute less than half of the planes in the air, I'd say. $\endgroup$ – Fab Sep 26 '17 at 21:36
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There's roundabout 400 paved runways over 2438 m (8000 ft) in the USA and EU, respectively, and about 200 or so in China and Russia, respectively, so that's about 1200. They are long enough to deal with most aircraft. Some might be untowered or unavailable, but then there are other countries, too. Estimates for "commercial" airports worldwide run around 4000 (there are about 9000 IATA codes, apparently).

So, every suitable runway would have to accommodate around 2 to 10 aircraft.

You can have around 50 to 70 movements per runway per hour, though you need separation of up to 3 minutes to avoid wake turbulence if a smaller jet arrives after a heavy. Let's say 30 landings per hour, and we're talking about 20 minutes, just in terms of pure runway capacity.

Now, to get all those planes lined up nicely... Parking might get crowded, too, but I'd think it would be doable - just fill up taxi ways progressively (presumably you don't care about take-offs for a while). See this diagram of aircraft parking prior to the Tenerife disaster (where many planes diverted to the small Tenerife airport due to a bomb in Las Palmas).

enter image description here

At any rate, the practicalities would be daunting. Would be interesting to see a proper feasibility study.

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  • $\begingroup$ "There's roundabout 400 paved runways over 2438 m [...] You can have around 50 to 70 movements per runway per hour", but some of them may not have the correct QFU, or they intersect reducing the throughput. In practical probably only a part of them will be usable simultaneously, and the throughput could be affected by less easy movements on the ground. $\endgroup$ – mins Sep 26 '17 at 6:40

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