> How's that supposed to work with Instrument Flight Rules, for which you literally train by wearing glasses which block your view outside the window [0]?

If you're wearing "foggles" (the technical term is a "view limiting device"), you're legally required to have a safety pilot who is responsible for maintaining visual watch.

You never, ever wear those while flying solo.

> And how are you supposed to spot an airplane coming at you with a closing speed of 1000 mph (1600 kmh)?

First, this near-miss was with a refueling tanker, which only travels at normal large-jet speed and is quite large.

If it was a fighter jet, you're right, it would be very hard to see. But frankly, compared to a fighter jet, everyone else might as well be a stationary object in the sky in terms of speed and maneuverability - so you're just relying on the fighter jet not to hit you. (They also have onboard primary radar and other fancy toys - so you hope they have more situational awareness of non-participating aircraft.)

> The whole point of Air Traffic Control is to control air traffic. Sure, there's plenty of uncontrolled airspace where you do indeed have to look out for traffic, but it's uncontrolled precisely because it rarely if ever sees commercial traffic.

Most airspace below 18,000 feet is still "controlled airspace", even though you have to look out for traffic - including commercial traffic. The big jets don't like to stay down there any longer than they have to, but that doesn't mean they're not there.

Being on an IFR clearance only guarantees that you're deconflicted with other IFR traffic. There's always the risk that there's non-participating traffic, especially in visual conditions (VMC). Class A airspace and transponder-required airspace help reduce this risk, but it's never completely eliminated.

Also, more importantly: The military largely plays by their own rules, entirely outside of the FAA.

Not necessarily; the same remoteness that made cell signal sparse likely makes ADS-B ground stations unlikely. There has to be one in range for it to show up places like FlightAware. Plenty of dead spots; you can help expand the network! https://www.flightaware.com/adsb/piaware/build/

ADSB is not mandatory in the US below FL100 or FL180 (10000/18000 feet), that covers most helicopter flights.

It depends also on the website you are using to track. I have an ADSB receiver that publishes to multiple tracking websites (the same data, unfiltered), and not all of them publish all the data. Flightradar24 doesn't show most of the military aircraft - I can see them on my local tracking interface but they are not shown on their website.

I wasn't there and don't know all the facts, so I'm not going to attempt to assign blame in this specific instance.

But speaking generally, I'll just say: If you're flying in VMC conditions (good weather), you're always required to see-and-avoid. Even if you're on an IFR clearance. Everything else is just considered an aid for situational awareness.