Selling it for more than it costs to build.
Computer-based modelling, advances in our understanding of supersonic flight and sonic booms and a mature civil (and private) aviation industry make the profit case much more compelling than it was for the Concorde. (The real test will be in their engine.)
The Concorde was notorious for bleeding money.
Maybe the premium aspect will be enough, given that we have a bigger and bigger chasm between rich and poor, or maybe the economics of running it won't compete against sub-sonic, lower fuel consumption planes.
I see this stated all the time on HN, yet there's a whole section at the top of this very comments thread where people are talking about how very profitable the Concorde was.
One person quoted the line "There were times, in fact, when the seven aircraft in the fleet would contribute around 40 per cent of BA’s entire profits."
(the 40% figure is more an indication of BA's sometimes thin margins than massive unfulfilled potential)
If the Concorde had been an actual financial success they would have developed it further and made a successor. And if BA and Air France had thought that the Concorde would continue making them money they wouldn't have retired it after one tragic accident in 30 years of operation. The 737 Max is still being made after much worse.
Which isn't to say Boom may not succeed.
NYC to London or Paris? Sure.
But now you still need to find people willing and able to spend $5K+ each way. I'd like to do it but realistically I'm not going to.
La Première will regularly go for $20k one way.
British Airways business class-only flights from the City airport have been off and on. Don't know their current status. I could afford business but it seems like a poor value relative to other things I could do other than maybe a co-pay with miles trans-Pacific.
I.e. you aren't trying to figure out "How do I 100% capacity a 8:17am daily flight?" (traditional subsonic carriers) but rather "How much demand is there per week/month?" (Boom)
If the flight is Wednesdays-only, then folks line their travel up on Wednesday. Because the alternative is a much longer flight.
Even for tourism, I wouldn't.
If they go for the low-rich market, their target customer moves schedules around themselves. If a CEO can't be in Europe until Wednesday, then the meeting happens Wednesday.
And the key thing Boom will be selling is literally unique: fewer hours on a plane.
To some, that's a nice to have. To people who hate being on a plane, it's worth a lot.
And even lie-flat first class sucks... it's nice, but you're still crammed into a dehydrating box.
And trans-Atlantic flights just aren't all that long. I'd pay some premium to avoid a red-eye but not likely $5K-$10K even if I could. That's probably about what I'm paying for a whole 3 week trip today.
You don't buy first class, or even business class seats, as far as I can tell from this comment. You have to set aside your own reactions because you aren't in the target market.
BA and Air France understood that people paid extra to be able to quickly travel transatlantic[0]. That premium value proposition depends heavily on passengers' expectation that the flight WILL go at the scheduled time. The airlines had to invest significant extra resources in spare parts, additional staffing, and standby airframes to ensure on-time performance.
If the Concorde were to ever develop a reputation for six-hour departure delays or days of cancellations in a row, no one among their premium customer base would bother paying extra for it.
British Airways and Air France did profit from them prior to the 9/11 hijackings and the flight 4590 crash, so it's not an impossible hurdle to clear for Boom. But the value proposition for a new SST is going to be vulnerable to operational concerns that don't affect the rest of an airline's fleet.
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[0] https://omegataupodcast.net/166-flying-the-concorde/ - "Every now and then they'd have a survey amongst the regular passengers [...] 'What do you think you paid for your Concorde flight today?' These people haven't got a clue what they paid for their Concorde flight today. They just tell their secretary, 'book me on tomorrow's Concorde, I need to get to New York in a hurry!'"