Before he became the first American to orbit the Earth, John Glenn was famous for another pioneering achievement.
In 1957, he became the first man to fly across the country faster than the speed of sound, traveling from California to New York in just three hours and 23 minutes.
Glenn’s aptly named “Project Bullet” seemed at the time to herald a new age of supersonic flight, in which passengers could cross the globe in an afternoon, thanks to American ingenuity and technological prowess.
Yet, 61 years later, supersonic commercial aviation remains an unrealized dream.
Beginning in 1969, the Concorde proved that routine commercial supersonic flight was technically feasible. It carried passengers at an altitude high enough to see the curvature of the Earth and flew them fast enough to outrun a sunset.
But for all its splendor, the Concorde had problems. It was an expensive, government-subsidized gas guzzler that flew just one commercially viable route—shuttling wealthy passengers back and forth between New York and London.
When it was retired from service in 2003, it left a void. Today, no commercial supersonic transport exists.
Now, a new generation of engineers and entrepreneurs at companies such as Boom, Aerion, and Spike are trying to change all that.
In the half-century since the Concorde was designed, aerospace engineering has made tremendous advancements. Carbon composites are making it possible to build lighter, more heat-resistant aircraft. Today’s jet engine technology permits aircraft to reach supersonic speeds without the need for Concorde’s inefficient afterburners.
If these entrepreneurs succeed, their efforts would constitute a giant leap forward toward the goal of routine, inexpensive supersonic travel.
Frequent fliers may be surprised to learn that one of the biggest barriers these companies face is neither economic, nor technological; it is regulatory. In 1973, the Federal Aviation Administration banned flights exceeding Mach 1—the speed of sound—over the United States.
The FAA indicated it adopted an overland speed limit to protect the public from sonic booms, the shockwaves generated as aircraft push through the air faster than sound.
In the late 1960s, before the Concorde even took flight, there was considerable concern that frequent booms could frighten livestock, shatter windows, or damage physical structures.
In fact, beginning in the late 1950s, the U.S. government conducted a series of tests on the effects of sonic booms. One study in Oklahoma City subjected residents to daily, frequent sonic booms for six months and found that “an overwhelming majority (73 percent) of the public felt they could live with” them. The public, it seemed, hardly considered sonic booms to be intolerable.
Nor were frequent booms found to be damaging to physical structures. In a 1964-65 test at the White Sands Missile Range in New Mexico, investigators subjected a small artificial community to 30 booms a day. The results: Houses constructed of typical materials experienced only the slightest damage when subjected to booms far more intense than those generated by the Concorde.
The investigators found, for example, that paint may chip on plasterboard ceilings when subjected to “repeated booms” with an overpressure of 5 pounds per square foot, the measurement of a sonic boom. Poorly mounted glass chipped at an overpressure of 12.1 pounds per square foot. Items began to fall off walls at 10.4 pounds per square foot.
But NASA data shows that the Concorde, cruising at 52,000 feet at Mach 2 (about 1,500 miles per hour), had a sonic boom of only 1.94 pounds per square foot.
The ill effects of overland supersonic flight seem to have been exaggerated. So, why did the U.S. government ban it? While the FAA’s rule appeared to be a noise abatement measure, it might have had more to do with saving face than saving the public from sonic booms.
Britain and France launched their joint Concorde project to much fanfare in 1962. That same year, the Soviet Union announced development of its own SST, the Tu-144.
Not to be outdone, President John F. Kennedy wanted an American-made supersonic transport aircraft that outdid them both. The result was the Boeing 2707, a government-funded Mach 3 giant that could carry 300 people. But the program foundered and was canceled in 1971.
Perhaps not coincidentally, the ban on overland supersonic flights went into effect two years later and closed the vast majority of the U.S. market to Concorde operations.
Whether the overland supersonic flight restriction was an act of protectionism, a genuine noise abatement rule, or some mixture of both is impossible to say.
While the Concorde’s sonic boom might not have been dangerous or damaging to property, it was certainly loud and jarring, exceeding 100 decibels. That’s roughly equivalent to standing next to a loud lawn mower.
Regulations to limit the nuisance of frequent and especially loud booms are reasonable, but does that require banning all supersonic flight?
For at least three reasons, the answer is no.
First, since the intensity of sonic booms depends on factors such as aircraft speed, weight, and design, advancements in technology can mitigate them. The Concorde was a heavy aircraft, weighing more than 400,000 pounds at takeoff, and it was a first-generation design.
The latest supersonic transport designs show that the Concorde’s unpleasant boom was inherent to Concorde, not to supersonic transports in general. They promise substantial improvements in boom intensity even when traveling at speeds faster than the Concorde, reducing the “boom” to something more like a “thump.”
In fact, just weeks ago, NASA awarded a $248 million contract to Lockheed Martin to build a “quiet” supersonic demonstrator aircraft, with the intention of testing it over American cities to see how residents react to subdued booms.
Second, closing the overland market to all supersonic flights effectively eliminated the economic incentive to innovate and develop quieter, more efficient, second- and third-generation supersonic transports.
In 2000, the cutting-edge commercial supersonic transport was the same aircraft that was flying in 1969. In what other high-technology field can the same be said?
Finally, the Aircraft Noise Abatement Act of 1968—the authorizing legislation for the overland speed limit—nowhere indicates that Congress intended to ban all supersonic flight, or even thought that a ban was good policy.
That law required the development of “standards to measure aircraft noise and sonic boom” and “regulations to control and abate”—but, critically, not eliminate—those conditions.
While developing these regulations, the FAA was directed to “consider whether the standard or regulation is economically reasonable, technologically practicable, and appropriate for the applicable aircraft … .”
It’s difficult to square that legislative mandate with the FAA’s eventual supersonic ban, but this isn’t the only time the FAA has taken a highly precautionary approach to rulemaking. When Congress directed the agency to integrate drones into the national airspace in 2012, for example, the FAA proceeded to ban commercial drone operations altogether.
A better path forward would be to eliminate the overland supersonic speed limit in favor of a reasonable, technically feasible noise standard that takes into account all the noises we already live with every day.
If people can tolerate a 90-decibel motorcycle, they should be able to tolerate an equivalent sonic boom. This would accomplish Congress’ original goal of limiting the nuisance caused by sonic booms without arbitrarily killing supersonic aviation.
Congress has already expressed interest in this approach. In 2016, the House Freedom Caucus identified the overland rule as one of the first regulations lawmakers and the Trump administration should target for elimination.
The Senate’s latest draft of the FAA reauthorization bill includes language proposed by Sens. Mike Lee, R-Utah, and Cory Gardner, R-Colo., that would require the FAA to develop a rule to permit “the development, testing, manufacturing, and operation of civil supersonic aircraft.”
The agency would be required to specify an “economically reasonable and technologically practicable” noise standard for sonic booms.
The FAA, to its credit, has already embarked on that course, with plans to “propose updates and additions to the noise-certification rules” for new supersonic aircraft.
Thus, Congress has an opportunity to advance the ball on supersonic aviation and bring greater certainty to the nascent supersonic sector by repealing the ban on overland supersonic flights.
Not that long ago, everyday Americans made heroes of the pilots with “the right stuff,” dreaming that soon they, too, would break the sound barrier. That was no flight of fancy. After all, in a single lifetime, aviation had progressed from the Wright brothers’ wood-and-canvas fliers to rocket-powered X-planes that reached the edge of space.
That dream may have stalled, but today’s engineers want to revive it. Their success will bring distant parts of the world closer together.
And maybe when we hear a sonic boom overhead, we’ll look up not with annoyance, but with awe at what human ingenuity can accomplish.