When the experimental XB-1 aircraft broke the sound barrier three times during its first supersonic flight on 28 January, it did not produce a sonic boom audible from the ground, according to US company Boom Supersonic.

“This confirms what we’ve long believed: supersonic travel can be affordable, sustainable and friendly to those onboard and on the ground,” said , founder and CEO of Boom Supersonic, in a .

As an aircraft pushes through the atmosphere at a high speed, it changes the air pressure around it, creating sound waves. And when a supersonic flight surpasses the speed of sound – Mach 1 – these sound waves combine to form a shock wave that spreads away from the flight path. This sonic boom can travel far enough to reach the ground, where it can produce an extremely loud noise, rattle buildings and even break glass.

Sonic booms over land are so disruptive that they contributed to the retirement of the fabled commercial airliner Concorde in 2003 and spurred many countries to prohibit commercial supersonic aircraft. Since then, aerospace engineers have been trying to develop aircraft designs that can go supersonic without the accompanying boom.

In this case, the XB-1 took advantage of a physics phenomenon called the Mach cutoff. Because sound moves more slowly at higher altitudes, an aircraft breaching the sound barrier at those heights will produce a boom that cannot reach the ground – if the boom moves downward, the increasing speed of sound will deflect it, pushing its shock waves upward instead.

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The trick is that temperature and wind also affect sound speeds, so the ideal altitude and speed for a supersonic aircraft will depend on atmospheric conditions. “The actual challenge is getting very accurate atmospheric forecasts on temperature and on wind – computing the practical Mach-cutoff flight speed is pretty straightforward from there,” says at the German Aerospace Center.

Boom Supersonic says that XB-1’s most recent and final test flight, on 10 February, also reached supersonic speeds without producing a boom. Now the company is using what it learned from the test flights to help its future commercial airliner, Overture, achieve the same feat. Supersonic overland flights would be up to 50 per cent faster than today’s commercial airliners. That could shorten the air travel time from New York to Los Angeles by 90 minutes.

But performing the Mach-cutoff flight “burns more fuel on the same distance than both subsonic and supersonic flight”, says Liebhardt. That makes it less economically viable than a regular supersonic flight and “the worst speed to fly at for fuel economy”. He sees Mach-cutoff flights as being more of a niche use case for “supersonic business jet users”, rather than for commercial airlines.

Fighter jets that first flew in the 1970s can be transformed into a fine powder and used to 3D print components for the next generation of aircraft in the UK’s Royal Air Force (RAF). Experts say this is a more efficient way to make aircraft – it’s less environmentally damaging and also solves the problem of sourcing materials from countries that are under sanctions, like Russia.

at Additive Manufacturing Solutions has developed a technique to recycle crucial materials like Ti64 – which is titanium with 6 per cent aluminium and 4 per cent vanadium. The UK Ministry of Defence has large quantities of expensive and hard-to-source materials like Ti64, but they are tied up in obsolete or broken aircraft and in stored components.

The company was able to take turbine blades from a Panavia Tornado – an aircraft in service with the RAF from 1980 to 2019 – and recycle them into a nose cone for a prototype engine that will power the RAF’s next generation of fighter jet.

“The world is more expensive than it used to be. It’s more complex and more expensive to make products,” says Higham. “We can make them as cost effectively as possible.”

Higham says that creating spherical particles from the old parts is key to printing quality new parts, as jagged particles can get stuck in the 3D printer. Simply grinding the metal down won’t do, so the recycled components are melted and then sprayed into a high-pressure jet of argon, where they break up into raindrop-shaped droplets. These droplets spin in the gas, become spherical then drop out and solidify. “It’s a very similar process to the way that rain becomes hailstones,” says Higham.

The resulting powder can then be fed into 3D printers. These machines essentially weld the powder into layers half the thickness of a human hair and set down each layer, one by one, to build the new part. “It’s a very straightforward microscopic welding process. It isn’t really anything more complex than that,” says Higham.

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In this first case, the powder was used to 3D print a nose cone for an Orpheus jet engine, which Rolls Royce is currently developing for the (FCAS). The FCAS includes a range of aircraft with modular components, including the BAE Systems Tempest – a proposed sixth-generation fighter jet destined for the RAF.

The experimental XB-1 aircraft, made by US company Boom Supersonic, flew faster than the speed of sound on 28 January. The achievement is the first time any civil aircraft has gone supersonic over the continental US – and another step toward the possible return of supersonic commercial aviation.

“This jet really does have a lot of the enabling technologies that are going to enable us to build a supersonic airliner for the masses,” said Greg Krauland, former chief engineer for Boom Supersonic, during a live stream of the test flight.

At the Mojave Air & Space Port in California, Boom Supersonic’s chief test pilot Tristan “Geppetto” Brandenburg took the XB-1 on its twelfth successful test flight and its first supersonic one. The sleek white prototype, with a blue-and-yellow tail assembly, broke the sound barrier on the first pass in the test airspace, reaching a speed of about Mach 1.11. Then Brandenburg flew back around for two more supersonic runs before returning to land.

The only aircraft currently able to reach supersonic speeds are military fighter jets and bombers. Although the fabled commercial airliner Concorde made transatlantic flights for several decades starting in the 1970s, it retired in 2003 due to multiple challenges, including high fuel costs and a deadly accident in 2000 that killed all 109 people on board.

The success of the XB-1 could herald a return for supersonic commercial flight. The test flights are meant to inform the design of a planned that Boom Supersonic says would cruise at Mach 1.7 and carry up to 80 passengers. The company plans to start producing these airliners this year and begin carrying passengers on them in 2029 – and airlines like United and American have already placed orders.

Other supersonic aircraft are also in the works, including from multinational company Dawn Aerospace and US space agency NASA. Fresh off the milestone XB-1 flight, Brandenburg teased a future demonstration that also involves NASA – possibly hinting at a future joint flight with both the XB-1 and NASA’s X-59 experimental aircraft. The X-59 is designed to minimise the shock wave that normally accompanies supersonic flight in order to create a sonic thump rather than a disruptive sonic boom.

“We’re working with NASA on something that I’m pretty excited about,” said Brandenburg.