There was a time when airline executives believed supersonic flight would become ubiquitous on long-haul routes. As the original supersonic aircraft were being developed in the 1960s, American Airlines publicly predicted a fleet of 200 supersonic aircraft operated by US airlines alone. It seemed obvious to the men running airlines in the 1960s that the public would demand more speed on long-haul travel and that airlines would need to be capable of flying from, say, New York to Frankfurt in four hours.  

The Aérospatiale-British Aircraft Corp. Concorde first flew in 1969 and entered service in 1976. But ultimately only 20 Concordes were built and only two airlines, Air France and British Airways, operated them. The Concorde was retired for good in 2003.

I bring up this history to temper expectations in the aftermath of United Airlines’ news that it has ordered 15 Boom Overture supersonic aircraft, with deliveries starting in 2029. United became the first North American airline to commit to the Overture; Japan Airlines is an investor in Boom and has options to acquire as many as 20 aircraft.

But there are obstacles ahead for any airline looking to launch a new era of supersonic travel.

For starters, the engine that will power the aircraft has yet to be developed. Boom has a partnership with Rolls-Royce to develop the engine, but it is still very much in the drawing-room phase. Until a prototype engine is built and tested, there are many uncertainties. And almost all recent new aero engine programs have been beset with delays and technical issues.

Secondly, what fuel will be used to power the aircraft? One of the problems with the Concorde was that it required much more fuel than subsonic aircraft, yet carried far fewer passengers than widebodies such as the Boeing 747. Airlines are always seeking fuel efficiency, and supersonic aircraft are not fuel efficient.  

Given the airline industry’s push to become carbon neutral, there is no way the Boom jets will fly with traditional aviation fuel. Indeed, Boom pledges that the Overture aircraft “will fly on 100% sustainable aviation fuel.”

Sustainable aviation fuels (SAF) are available and used by some airlines, but they are much more expensive than conventional fuel and far less available. So until an engine exists and significant change is made in the cost and availability of SAF, it is hard to take Boom and United too seriously.  

Then there is the issue of whether there will be passenger demand for a Mach 1.7 speed aircraft. The Overture is designed to carry between 65 and 88 passengers. Given the elaborate, private suite business-class products airlines now offer on long-haul flights, how many passengers will be willing to trade beds and private workspaces for a few hours less in the air?  

There is also the question of scheduling. Shorter transatlantic flights, for example, could pose problems in terms of slots and airport night curfews.

Finally, there are the route limitations driven by current regulations. The US and Europe currently ban supersonic flights over land. Unless that changes, the routes that the new aircraft will be able to fly will be severely curtailed.   

United would be able to use the aircraft to fly from New York to London or from San Francisco to Tokyo. But routes such as Los Angeles-London or Chicago-Amsterdam would require overland flying.  

Another intriguing possibility in the US would be to put the aircraft on transcontinental routes frequented by business travelers, such as Washington DC or New York to Los Angeles. But that would require a change in regulations.

Boeing recently abandoned its plans for developing a new supersonic jet, saying the business case could not be made. What do Boom and United know that Boeing does not?

For the aircraft to be viable financially for airlines, the Overture will have to be viewed as more than a bucket-list experience for curious passengers. United will need passengers flying the aircraft on a regular basis, particularly business travelers, to make it work financially.

These hurdles, of course, can be overcome, but they exist. Airlines and the broader air transport industry will need to approach any new supersonic era with a clear understanding of the challenges ahead.

Aaron Karp/ATW [email protected]