> How many deaths would communicate "We have likely reached system failure"?

"Failure" is really a matter of opinion rather than some objective tipping point. The air system is unlikely to ever actually "fail", and at worst will just become some arbitrary level of degraded that some people will loudly label "failed".

There are plenty of examples around the world of countries with variously degraded air systems, that are far worse than the US status quo but still are not "failed".

There's Egypt, which has labeled crashes caused by bad design as "someone used a bomb and blew it up" for political reasons: https://www.theguardian.com/world/2018/jul/07/fire-not-bomb-...

Yemen, in the midst of a perennial civil war, still runs commercial flights: https://www.pprune.org/terms-endearment/653181-yemenia-expat...

Russia, with airplane parts sacntioned for years, still runs commercial flights.

Even if the US undergoes a USSR-style sudden collapse, the aviation system is not going to "fail" in the sense of completely breaking and stopping.

>Yemen, in the midst of a perennial civil war, still runs commercial flights

Not any more, they don't:

> The General Director of Sanaa International Airport, Khaled al-Shaief, said in a post on his X account that the strike had completely destroyed the last of the civilian planes that Yemenia Airways was operating from the airport.

https://www.reuters.com/world/middle-east/israel-says-it-has...