Between 1976 and 2003, you could fly from London or Paris to New York in under four hours. The aircraft doing it was Concorde, the supersonic passenger jet that cruised at Mach 2, roughly twice the speed of sound. For 27 years, Concorde represented the future of commercial aviation. Then it stopped flying, the aircraft were retired, and no commercial supersonic service has resumed since.

Commercial supersonic passenger travel has been technically possible for decades. It is not currently happening because the economics do not work, not because the technology has been lost. The story of why we stopped flying supersonic, and whether we are going to start again, is specific and worth understanding.

Why Concorde was retired

Concorde was the joint product of British and French aerospace companies, announced in 1962 and entering commercial service in 1976. It was operated by British Airways and Air France on a small number of premium routes, primarily between Europe and New York.

The aircraft was a remarkable engineering achievement. It cruised at 60,000 feet, well above conventional traffic, and flew the Atlantic in about three and a half hours. Passengers paid premium fares (a transatlantic Concorde ticket was typically several times the cost of a first-class ticket on a subsonic flight) and got a genuinely faster journey.

The retirement in 2003 was caused by several factors converging. The aircraft was aging, and the specific components it used (including custom-machined parts from suppliers that had stopped making them) were becoming expensive to maintain. A 2000 crash of Air France Flight 4590 at Paris Charles de Gaulle killed 113 people and grounded the fleet for over a year. When Concorde returned to service, passenger demand had not fully recovered, partly because of the September 11, 2001 attacks on the United States. British Airways and Air France announced retirement simultaneously in April 2003, and the last commercial flights operated in October.

No single factor retired Concorde. The combination of rising maintenance costs, aging airframes, reduced demand, and the difficulty of justifying continued operation to shareholders ended the service.

The three problems with supersonic flight

The technical reasons why supersonic commercial aviation is harder than subsonic come down to three specific challenges.

The first is the sonic boom. When an aircraft flies faster than sound, it produces a continuous shock wave that reaches the ground as a loud boom. The boom carpet (the area below and behind the aircraft where the boom is audible) can be 50 miles wide and extends the entire length of the supersonic portion of the flight. In populated areas, repeated sonic booms are extremely disruptive.

The sonic boom is the reason commercial supersonic flight over land has been banned in the United States since 1973. Concorde could only fly supersonic over water. Its routes from Europe to New York were planned around coastal approaches that minimized over-land supersonic segments.

The second problem is fuel economy. Supersonic flight is dramatically less fuel-efficient per passenger mile than subsonic flight. Concorde burned approximately three times the fuel per seat mile of a contemporary 747. This made supersonic service expensive to operate and vulnerable to fuel price swings.

The third problem is payload. Achieving supersonic flight requires specific aerodynamic choices (slender fuselage, delta wings, highly swept leading edges) that limit the number of passengers the aircraft can carry. Concorde seated about 100 passengers in a configuration that a similar-sized subsonic aircraft might carry 150 to 200. Revenue per flight was limited by the passenger count even at premium fares.

Why we have not replaced Concorde

In the 22 years since Concorde's retirement, several companies have announced supersonic passenger aircraft projects. Boom Supersonic is the most prominent current effort, with the Overture aircraft planned to enter service later in the 2020s. Aerion Supersonic announced an AS2 business jet but closed operations in 2021. NASA has been working with Lockheed Martin on the X-59 QueSST experimental aircraft designed to produce a quieter sonic boom.

The technical challenge has not changed since Concorde. The economic challenge has, if anything, gotten harder. Modern subsonic aircraft like the Boeing 787 and Airbus A350 are dramatically more fuel-efficient than the aircraft Concorde competed against. The speed premium a supersonic aircraft would offer has to justify a much larger fuel cost relative to modern subsonic options.

The market segment that Concorde served (wealthy business travelers crossing the Atlantic on short notice) has also changed. Business class on a modern widebody offers a flat bed, full privacy, high-quality meals, and Wi-Fi that allows productive work. A supersonic aircraft with conventional seating that gets you there in three hours instead of seven may be less appealing than a subsonic option where you sleep lying down for the whole crossing and arrive rested.

The sonic boom problem and the quiet boom research

Recent research has focused on reducing or eliminating the sonic boom, which would allow supersonic flight over land and dramatically expand the viable route network.

The approach is to shape the aircraft's body such that the individual shock waves produced by different parts of the aircraft cancel each other out or merge into a much softer "boom." A conventional supersonic aircraft produces a loud double-crack at ground level, around 100 to 120 decibels at the peak. A shaped aircraft might reduce that to something closer to a distant thud at 75 decibels.

NASA's X-59 QueSST is a research aircraft designed specifically to test this approach. The goal is to produce a sonic boom quiet enough that it can be approved for routine over-land supersonic flight.

If this research succeeds, it would transform the economics of supersonic flight. Current proposals for supersonic aircraft have to route around populated areas, which limits their commercial viability. A quiet-boom aircraft could fly direct supersonic routes over land, opening up markets like Los Angeles to New York, London to Rome, or Sydney to Tokyo that are not practical for conventional supersonic flight.

What a modern supersonic aircraft might look like

Boom Supersonic's Overture is the most mature of the current supersonic projects. The aircraft is planned to carry 64 to 80 passengers at Mach 1.7, cruise at 60,000 feet, and have a range of about 4,250 nautical miles. Operational service has been projected for the late 2020s, though timelines have shifted repeatedly.

The Overture uses four engines, a change from Concorde's four-engine configuration primarily to accommodate sustainable aviation fuel and reduce noise at takeoff. The aircraft is designed to fly either over-water supersonic routes or, if quiet boom technology becomes available, over-land routes as well.

The business model assumes premium fares, aimed at business travelers willing to pay several times the subsonic fare for the time savings. The target market is routes where the time saved is meaningful: transatlantic, transpacific, and certain Asian intercontinental routes.

Whether the aircraft reaches commercial service on time and whether the economics work is uncertain. Every previous supersonic passenger project since Concorde has either been canceled or delayed significantly beyond original timelines. The engineering challenges are real, and the commercial case has to be strong enough to justify multi-billion-dollar development costs.

The quiet conclusion

Concorde's retirement was not the end of a technology story. It was the end of a specific commercial story in which a particular aircraft, operated by specific airlines, could not sustain its niche. The engineering capability to fly supersonically has existed since the 1960s and continues to improve.

Whether commercial supersonic passenger flight returns in the 2020s depends on three things: whether quiet boom technology is mature enough to allow over-land routes, whether fuel economy improvements are sufficient to make the operating cost acceptable, and whether the premium market will pay the fare premium that supersonic service has to charge.

If those three things align, we will see a supersonic passenger aircraft in commercial service within the decade. If they do not, the Concorde era will remain a specific historical episode rather than a precursor to a new generation of fast aviation. The technology is ready. The economics are still the question.