Almost 20 years on from Concorde’s last supersonic flight, a new generation of jets that will travel at speeds faster than that at which sound carries is being developed by a clutch of U.S. start-ups. But with the downfall of the Europe-designed Concorde in large part due to noise pollution restrictions on flying over populated areas of the USA, new regulations are being drawn up by American aviation authorities.

The current regulations on how much noise jets flying over mainland USA were written back in 1978 in a response to the ‘noisy’ European Concorde. At the time, the U.S. had no equivalent to the Concorde of its own and the ban was a result of political pressure. And while the new generation of jets being developed by start-ups and tested by NASA will be quieter than Concorde was, they will not yet be permitted to break the sound barrier over continental USA.

However, new regulations being drawn up will allow for the fact that the design of superfast jets means their engines will have to be slightly louder than those of standard passenger aircraft. In an effort to avoid the same diseconomies their own noise level regulations resulted in for Concorde, U.S. authorities are lobbying for new global rules.

But in a role reversal of previous decades, Europeans policy makers are expected to represent the most significant hurdle. They reportedly want to keep noise levels similar to those achieved by the latest Airbus and Boeing models. Despite the fact their top speeds have remained largely stable for 60 years now.

Start-up Boom Supersonic is developing Overture, a three-engined jet scheduled to enter service at some point in the mid-2020s. The largest of the three models currently being worked on, the Overture is built to hold 65 passengers and can travel at over twice the speed of sound at up to 1700 mph. That will make it slightly faster than Concorde was.

However, technological advances mean it will make significantly less noise than its European ancestor as well as use alternative fuels that will reduce carbon emissions. It will make a sonic boom when it speeds up over routes crossing oceans but its engineers say it will be only about a thirtieth as loud as the one Concorde made.

The other two smaller supersonic models currently under development are the Aerion Supersonic AS2 and the Spike S-512. Both are built for smaller numbers of business passengers and can reach around one and a half times the speed of sound – Mach 1.5.

NASA itself is also working on a supersonic jet, the QueSST. It has been designed to make no sonic boom when breaking the sound barrier and development is scheduled for completion this year, with the first test flights taking place in 2021.

Environmentalists are fighting the introduction of the new generation of supersonic jets, saying they will produce as much as seven times higher emissions than subsonic equivalents. But the companies behind them insist the latest technology will reduce both emissions and noise levels. Gene Holloway, Aerion’s chief sustainability office commented for the Aerospace America periodical:

“We fully recognise that we are going to pump out more greenhouse gases than a subsonic aircraft will. That’s just the laws of physics.”