[1] excluding some very different modes of air travel, like lifting gas based aircraft.
We're looking at years before people will feel it's safe to travel again and borders are reopened to tourism.
No industry can survive that long without revenue. Once major portions of the civil aviation industry, and it's supply chains, start going into receivership it's going to take a very long time to get it started again. Unmaintained equipment decays, and employees who have found other jobs won't necessarily come back to their old jobs when their ex-employers want them.
Restarting the aviation industry after a multi-year shutdown will require rebuilding a lot of hardware, (re)hiring a lot of people, and rebuilding a vast amount of institutional knowledge. This will take years or even decades--and I wouldn't want to fly on the first airliner to come off a restarted production line staffed mostly by new employees and flown by pilots without much recent experience.
No one has ever needed to attempt restarting an entire industry since the demilitarization of the economy following WWII, and it's unclear if it's even possible anymore.
By the time all is said and done, most people may well be used to doing things other than flying and the demand might not even re-emerge.
https://www.theguardian.com/business/2020/sep/21/airbus-reve...
Vacations will still exist.
A lot of air travel is completely needless and only done "because we can".
A 2-person sleeper car used to cost a bit less than 2 coach tickets on a plane, at the expense of a 66-hour delay (plus another 6-12 hours of actual delays). And it was glorious.
Okay, you didn't always have the time. But when you did, Amtrak was the way to go. That book you meant to read? Done, along with the pulp novel you didn't really mean to read. Side projects? Easy to work on when you're watching the continental US from an observation car with a transparent ceiling.
And the meal cars. I am going to miss the meal cars, which Amtrak was phasing out even before covid because "my generation doesn't like taking to people". But in the past 5 years, those meal cars were the only place where I got to candidly talk with a more or less random slice of the American population. And that's including my cross-country road trips!
You got free meals with a sleeper car, but there was only one dining room and seating was random, so you'd see different people every meal. And you'd just talk, politely, for about an hour with people who you probably would have never otherwise interacted with.
I miss that.