[redis_mlc]

> Surely there are places to park planes in bulk

No, there aren't for airliners. Most are in the air at any given time.

There's boneyards and mfg. airports, and that's about it.

A possibility would be a non-operating airport in a friendly country - thinking about the new Berlin airport.

Boeing likely finally stopped making the 737 MAX after they ran out of parking space, which forced a decision.

To park even one airliner long-term requires prior permission and monthly payments.

[jimktrains2]

We ended up having to do this during 9/11. I don't know if there are relatively more or fewer planes than then now, but I do remember that many/most airports had Jets parked on the runways and we're nearly all of their taxi- and runways for storage.

[orange_fritter]

I have no knowledge on this topic, but weren't most/all *US flights grounded during the 9/11 attacks?

[p_l]

It involved flooding various airports (especially in Canada) with planes that were already in the air destined to USA, others ended up diverting inside USA, generally lots of congestion and abnormal parking.

Slots are used to regulate congestion in normal conditions.