The US Is Making It Easier to Test Supersonic Commercial Jets

The Federal Aviation Administration wants to make it easier to test supersonic commercial airplanes, and has just proposed new rules that would help usher in a new era of faster-than-sound civilian jets. We are nowhere near the point where the successors to Concorde take to the skies, but the new rules would be a necessary step in the right direction.

Several private companies want to bring back supersonic commercial jets. If they manage to deliver on schedule, we might be able to cross the Atlantic in three hours again sometime in the mid-2020s, more than two decades after a Concorde landed for the last time, in 2003.

At the Paris Air Show on Monday, the FAA's Acting Administrator Dan Elwell said that his agency wants to ease the rules governing the tests of supersonic aircraft in US airspace. In the federal government's acronym-heavy jargon, what the agency just announced is called an NPRM — a Notice of Proposed Rulemaking. In practical terms, it means that those companies will be able to more easily test their aircraft, once they fly. That's going to take years, by the way: nobody has actually flown a prototype yet.

The FAA says in its fact sheet on supersonic flight that it wants to publish the first notice, making it easier to test supersonic jets, by the end of this year. The second one, related to the noise certification of supersonic aircraft, would be published by March 31, 2020.

And that "noise certification" is exactly where the problem is.

Flying faster than sound is not much of a technological challenge these days. Concorde, a 1960s design, had a long, illustrious and safe career at Mach 2; its only accident happened on the runway, and had nothing to do with supersonic flight. It was due to a catastrophic fuel-tank rupture and subsequent fire. Materials and engine technology is advanced enough that keeping an aircraft in the air at 60,000-plus feet for many hours and Mach 2.2 is not difficult. The issue to solve is how to minimize the sonic boom it makes.

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That's why the FAA markedly points out that "the two supersonic rulemaking activities would not rescind the prohibition of flight in excess of Mach 1 over land." You're not going to be startled anytime soon by the scary thunder of a sonic boom made by a test aircraft; the agency says it is "assessing the current state of supersonic aircraft technology in terms of mitigating the noise impacts."

For all its glamour, Concorde could never do one key thing: It was never allowed to fly supersonic over land. It could accelerate past the speed of sound only over water, and that limited enormously its commercial appeal.

NASA is currently running tests with an F-18 fighter jet to see if "quiet booms" — essentially loud, low thumps rather than window-breaking thunderclaps — are a possibility. The private companies vying to build commercial supersonic jets are also working on designs that would keep the booms at acceptably low levels.

When that last piece of the supersonic puzzle is solved, a new generation of commercial supersonic planes will definitely take off.

Most are business jets with fewer than 20 seats, too small for viable commercial service and appealing mostly to billionaires in a hurry. A credible candidate for scheduled airline service is Boom Supersonic's 55-seat airliner, called Overture. It would fly at Mach 2.2, the same speed as Concorde, but with roughly half the passengers — yet with far better fuel economy. Boom's got the backing of Sir Richard Branson among others, and plans to fly a small-scale demonstrator called the XB-1 this year.

Getting to the point where the company can test-fly the real airliner will require years, though. But while we wait for that day to come, the changes the FAA announced in Paris are a key step in getting supersonic commercial jets to the sky again.