THE ‘Son of Concorde’ supersonic plane being built by Nasa has started testing its ‘quiet’ jet engines ahead of its first flight test.

The supersonic aircraft is called the X-59 Quesst – and it is expected to cut the flight from London to New York City to just 3.5hours.

To do so, it will have to cruise at altitudes of 55,000 feet at speeds of a whopping 937mph.

The X-59 Quesst is being built in a collaboration between Nasa and Lockheed Martin.

Test runs of the engine began in late October, at Lockheed’s Skunk Works facility in California, and will continue in phases.

Engineers ran the engine at low speeds without igniting it to check for any leaks in preliminary tests.

In fuelled expulsions of the engine, albeit at low power, the engine performed well, according to Nasa.

“The first phase of the engine tests was really a warmup to make sure that everything looked good prior to running the engine,” said Jay Brandon, chief engineer for the X-59, in a Nasa statement.

“Then we moved to the actual first engine start. That took the engine out of the preservation mode that it had been in since installation on the aircraft.

“It was the first check to see that it was operating properly and that all the systems it impacted — hydraulics, electrical system, environmental control systems, etc. — seemed to be working.”

The jet was expected to conduct its first test flight this year, however, its schedule has already been subject to delays.

Aerospace firms worldwide are racing for the chance to build the ‘Son of Concorde’ – the successor to the British supersonic jet that was banned in 2003.

Commercial supersonic flight over land has been banned in the US for more than 50 years, and about 20 years in the UK, because of the noise of sonic booms.

There have been no commercial aircraft even capable of hypersonic or supersonic flight since the Concorde.

The aircraft were banned in the UK because they were deemed too noisy and extremely expensive to operate.

With restricted flight availability, fares were often too high for most customers.

But with several manufacturers actively developing new supersonic aircraft, the UK’s aerospace watchdog has said it will review the ban.

The X-59 Quesst was designed to fly faster than the speed of sound without the banned ‘boom’.

Instead, a much quieter ‘sonic thump’ is expected to trail behind the jet, which is owed to its long and narrow build

This importantly gives the Nasa and Lockheed jet a low enough noise level to be able to fly over land.

In an official podcast last month, Lori Ozoroski, a project manager at Nasa explained that the Concorde had its flights drastically limited before it was banned because of the thunderous noise.

“[The Concorde] was limited during its flights that it could not fly, say into, you know, somewhere in the middle of the US. You were not allowed to fly supersonic over land.

“So most of the flights were back and forth just over the ocean. And so again, that ban has been in place for 50 years, over 50 years in the US. A lot of international countries as well have similar bans.

“And so the whole goal of this research that we’re doing right now is to lift that ban and set a speed limit for commercial supersonic aircraft rather than a speed limit.”