Boom Supersonic, a Colorado startup that is developing a new class of supersonic commercial aircraft, has raised $33 million in Series A funding. Backers include Y Combinator Continuity Fund, RRE Ventures, Palm Drive Ventures, Caffeinated Capital and 8VC. As part of the deal, YC president Sam Altman and former Sequoia Capital partner Greg McAdoo have joined Boom's board of directors.

Why now: It's been more than a decade since the Concorde was grounded, which was more about post 9/11 economics than supersonic technology. Boom is hoping to significantly decrease the cost-per-flight, in part because of two major development advancements since the time of Concorde:

1. Even though Boom is already testing in real wind tunnels, it can do a lot of simulation via software.
2. Companies like Boeing and Airbus have spent billions of dollars helping to develop and gain approvals for carbon fiber, which can help a plane go faster and use less gas.

Plans: Proceeds from this financing are expected to get Boom to its first supersonic flight in 2018 (a bit later than originally expected), with later plans to have passengers flying in the 2020's. Interim financing would be aided by a previously-announced $5 billion in pre-orders from companies like Virgin, with expectations that additional airline orders will be disclosed later this year.

Fun fact: The company's headquarters is on an old airfield, and its conference room was originally built as an airplane hanger.

Bottom line: There currently is a U.S. ban on supersonic flight over land, which is why Boom's initial plan is to run on existing supersonic corridors like LA-Tokyo and NYC-London. "The aircraft speed limit is one of the worst ideas in aviation policy history," Boom CEO Blake Scholl tells Axos. "Boom is working to overturn this, but not counting on that in our business model."