The Supersonic Boom

It was a painful decision for Boeing. The Seattle aircraft manufacturer announced recently it was delaying the first test flight of its supersonic transport by a year — to 1972 — because of technical problems. With 3000 employees at work on the SST and orders on hand totaling $5 billion, Boeing was in no mood to delay the controversial plane any longer. Boeing also knew that the Administration, which has committed $653 million to the SST so far, was facing growing congressional pressure to cut further SST funds. A delay, the company feared, would aid critics who want to ground the plane altogether.

But Boeing had little choice. The plane on the drawing boards is 50,000 pounds overweight — far too heavy to fly profitably across the Atlantic — and needs substantial design changes. Technical problems are not surprising in a new plane, especially one designed to fly 1800 mph (one mile every two seconds) and whose tail is bigger than the wings of a 707 jet. What is surprising is that Boeing was able, once again, to say little about the SST’s main technical problem: the loud thunderclap widely known as sonic boom.

“Le bang” and the SST

Whether Boeing talks about it or not, however, the boom speaks for itself. If the SST flew from New York to Los Angeles, for instance, 10 million people in a 50-mile-wide path beneath the SST would hear the boom. Depending on atmospheric conditions, it would sound like dull thunder in the distance or a firecracker 25 feet away. There’s no way known to eliminate it or even reduce it much. If fleets of SST’s crisscross the continent day and night, warns Senator William Proxmire (D., Wisconsin), the most outspoken congressional critic of the SST, “we will all live out our lives in an immense drop forge foundry.”

At best, sonic boom would be one more noisy nuisance, unnoticed by some, startling to others. At worst, it could cause fright, accidents, or even heart failure. In France last summer three workers were killed when the sonic boom from a French fighter (the French call it “le bang”) collapsed the roof of an old farmhouse. Sonic boom has also broken windows, cracked plaster, and knocked pictures off living room walls. The Air Force, which has been flying supersonic planes for nearly 20 years, has paid several million dollars in damages. In fiscal 1967 alone, the Air Force settled 3357 claims, totaling $440,000.

Hushing a problem of this stentorian magnitude is about as easy as hiding an elephant in a Volkswagen. Already a worldwide ban-the-boom movement is springing up. Canada and Sweden have outlawed boomproducing flights over their land, and Germany and Switzerland say they are prepared to do so. In the United States, Santa Barbara, California, and Dearborn, Michigan, have anti-boom laws, while similar legislation was recently introduced in New York City. Because the courts probably will invalidate such local laws on the grounds that they exceed a city’s legal jurisdiction, the United States needs a national antiboom law. Unfortunately, although Senator Clifford Case (R., New Jersey) introduced legislation in May to ban commercial SST flights over the United States, a federal law is unlikely in the foreseeable future; certainly the Administration doesn’t want to handicap a project it has backed from the beginning and which is slated to get at least $1 billion in government money if and when full-scale production starts.


Partly by default, the center for much of the ban-the-boom protest has not been Capitol Hill, but the Cambridge, Massachusetts, home of Dr. William Shurcliff, a fifty-nineyear-old Harvard physics researcher. A year or so ago, Shurcliff read several irate letters in the New York Times complaining about sonic boom. He wrote to nine of the letter writers expressing his concern and inquiring whether “I could contribute $10” to help fight the SST. Discovering that there was no private group against the boom, Shurcliff decided to form his own.

Today the Citizens League Against the Sonic Boom has over 2200 members, including many doctors, professors, engineers, physicists, and a “sprinkling of housewives in areas already badly boomed.” The League acts as a clearinghouse for all SST information, disseminates anti-SST literature, runs newspaper ads, and sparks letter-writing campaigns. Shurcliff himself answers an average of 35 letters a day, practically all against the SST or sonic boom. He is on the phone frequently with Senator Proxmire (“we have a Bill and Bill relationship”), feeding him information.

Bearing the brunt of the Bill and Bill attack — indeed, all the SST criticism — is Major General Jewell Maxwell, who heads the SST program at the Federal Aviation Administration. The Mississippi-born Maxwell, who is on leave from the Air Force, travels around the country speaking on behalf of the SST in a forceful yet charming manner. He mixes folksy anecdotes about stagecoach days with slightly chauvinistic rhetoric about the need to maintain the country’s commercial aviation leadership. Listening to Maxwell, one gets the impression that if we don’t build the SST, the United States will be relegated to the status of underdeveloped country.

He cites our balance of payments deficit, noting we have to meet the challenge of the Concorde, the British-French SST that will be flying some three years before Boeing’s. He reminds his audience that exporting a single Boeing SST “will pay for 20,000 Volkswagens, or 10 million Japanese transistor radios.” What he doesn’t say, however, is that the Institute for Defense Analyses, in a study commissioned by the FAA, found that the SST would not significantly improve U.S. balance of payments — and under certain conditions would worsen it.

When he comes to sonic boom, Maxwell admits “we have a problem.” But, in fatherly tones, he assures his listeners that the SST will fly supersonically only over oceans, away from populated areas. At a glance, this concession seems to solve the boom problem, especially since Boeing and the airlines generally agree that if sonic boom is a public nuisance, the SST should not fly over populated lands.

Sunny talk, economic forces

“We faced that decision two years ago,” says H. W. Withington, Boeing’s vice president in charge of the SST, and decided the SST is “worthwhile even if it never flies supersonically over land masses.” From Trans World Airlines, the first airline to order the Boeing SST, comes an echo. “Even with boom restrictions, the SST makes economic sense,” says Robert W. Rummel, TWA’s vice president for planning and research.

Such sunny talk aside, economic forces could easily pressure SST backers into seeking flights over populated areas. Boeing estimates it will sell a minimum of 500 SST’s by 1990 if the plane is banned over land, compared with 1200 if there is no ban. At $40 million per plane, Boeing will forfeit $28 billion — greater than its total sales for the last 15 years. Can we rely on corporate conscience to limit SST flights when the price is so high?

Such sales penalties are confirmed by the airlines. Says TWA’s Rummel: “We expect to have 50 Boeing SST’s by 1980 if there are no restrictions. If the plane is banned over land, my guess is that we will have bought between 25 and 35.” American Airlines, which has ordered six Concordes and six Boeing SST’s even though it flies no ocean routes, would probably cancel its orders if

supersonic flight is limited to overocean routes. Eastern, United, and other airlines that fly mainly domestic routes are in similar straits. Even Pan American World Airways, whose flights are largely over water or sparsely populated land, says a ban could force it to fly 17 percent of its planned SST routes at subsonic speeds.

Moreover, a ban would probably mean a higher fare to help airlines recoup the higher cost of flying the SST at less efficient subsonic speeds. To the airlines, a higher fare is no more desirable than a foggy runway, for it would surely cut passenger demand, removing the profits from SST flights for certain airlines.

The economic pressures will also bear down on the government, which expects to recoup its money if Boeing sells 300 planes. If Boeing sells 500 planes — which the FAA confidently says it will — the government will earn about 6 percent on its investment. But in making this estimate, the FAA again rejected the forecast of its own consultant, the Institute for Defense Analyses, which says only 279 SST’s will be sold if there are boom restrictions. Once more the FAA ignored the advice of its advisers, choosing only the information that fits the procrustean bed it and Boeing have carefully made for the SST.


In short, a ban on SST flights over land could mean the difference between profit and loss — for Boeing, the airlines, and the government. With so much at stake, all three have tiptoed about trying to muffle the boom issue. One of their most frequent arguments is that people will accept booms once they get used to them, just as they have accepted many other noises — from jet engines, motorcycles, pneumatic hammers, and the like — so common these days. An FAA brochure, in fact, states that “individuals tend to accommodate themselves to an initially disturbing noise once it becomes a pattern of life.” Boeing, more childishly effective at public relations, calls sonic boom “a twentieth-century sound.”

Clearly, the SST’s backers want to persuade the public to stop worrying and learn to live with the boom. As Senator Proxmire puts it, “The SST will start by flying the ocean routes. Soon the economic pressures of flying these high-cost planes on limited routes will force admission of the planes to a few scattered land routes. And ultimately they will be flying everywhere.”

Proxmire’s fear is not eased by the pronouncements of government officials. Alan Boyd, Secretary of Transportation, thinks the SST will be able to fly supersonically on portions of domestic flights. On a flight from Chicago to Los Angeles, he was quoted as saying in Science, the SST could fly subsonically to Denver, then supersonically from Denver to Los Angeles, where there are “lots of mountains, lots of desert, and very few people.” And General Maxwell “suspects there are land areas we will be permitted to overfly.” When pressed for details, Maxwell pleads ignorance. Asked by the House Appropriations Subcommittee last year whether the SST would fly over populated land, he replied, “We do not, at this moment, I feel, have sufficient understanding of what criteria we should employ to say an airplane would have acceptable sonic boom characteristics to be completely sure of this.”

But there is sufficient understanding of sonic boom “characteristics,” at least enough to predict its effect in most cases. To begin with, any airplane going through the atmosphere disturbs the air and creates pressure waves. These waves travel at the speed of sound, but fan out in all directions and are too weak to be heard. The only audible noise comes from the engine. When a plane travels supersonically, however, the waves of air molecules cannot get out of the way of the plane fast enough. They pile up and lag behind the plane, creating a shock wave that is heard on the ground as a sharp crack or thunderous roar, depending on the weather and other factors. Contrary to the popular notion, the boom does not occur only when the plane breaks the “sound barrier.” Like the wake of a ship, the boom is continuous as long as the plane is flying supersonically.

Boom and superboom

The boom’s intensity is measured in pounds per square foot (psf) of “overpressure” — the pressure wave created by the plane in excess of normal atmospheric pressure. Tests have shown that an overpressure of about 6 psf will crack plaster and an overpressure of 10 psf will shatter glass. The FAA says the Boeing SST will be under 2.5 psf, so will cause little or no property damage. But under certain atmospheric conditions, the Air Force has found that the boom produces a “focusing effect” that can amplify a 2.5 psf pressure to a glass-shattering 10 or 15 psf. Because no one seems to know exactly when this so-called superboom will occur, a pilot cannot fly around the atmospheric conditions that cause it.

Even without the focusing effect, the booms expected from the SST are bad enough. The same day that “le bang” killed three Frenchmen, the President’s Office of Science and Technology released the results of the sonic boom tests carried out the previous year over Edwards Air Force Base in California. The report indicated that from 33 to 98 percent of the people in the test objected to booms in the 2.0 to 3.5 psf range.

If this isn’t sufficient evidence for the FAA, it can restudy the now famous Oklahoma City tests. In 1964, the Air Force “boombarded” Oklahoma City some 1250 times I over six months. Boeing was quick to point out that “the overwhelming I majority feel that they could learn to live with the number and kind of booms experienced” in the Oklahoma tests. But even though Oklahoma City is heavily dependent on the aviation industry for the livelihood of many of its residents, a sizable number — 24 percent — said they could not learn to accept sonic boom. The 24 percent figure looms even larger considering that the SST will serve less than 5 percent of the population. What’s more, the tests were run during daylight hours only and were well publicized in advance. Many residents, in fact, used the 7 A.M. boom as an alarm clock.

All at sea

The evidence accumulated by Harvard’s Shurcliff suggests that even if the SST is limited to over-ocean flying, a typical transatlantic flight would boom about 4000 people aboard fishing boats, tankers, pleasure boats, and big passenger ships. The Swedish American line has publicly protested sonic boom, adopting the position of Bo Lundberg, former director general of the Aeronautical Research Institute in Sweden. Lundberg, one of the most persistent critics of sonic boom, wants extensive boom tests at sea. No one is sure, for example, that the boom won’t harm large schools of fish, but this is a consideration that Senator Warren Magnuson, from Boeing’s home state, obviously considers trivial: “Nobody yet has produced any testimony to show that the fish will write their congressmen,” he told the Senate last October.

Boeing has been studying sonic boom since 1958 and is now trying to reduce both the sonic boom wave and its duration. But Withington concedes that “changes in the level of sonic boom are coming very hard and slow.”There’s no breakthrough in sight, he says. “It’s just a matter of chipping away.”

$4.5 billion bird

Chipping away at the boom is no easy task. For one thing, the technological task of building an SST is so great that Withington says Boeing could not take a one percent performance penalty even if it meant a lower sonic boom. “We do not make design changes just to reduce sonic boom,” he says flatly.

The problem is compounded by airline requirements for a plane with a low operating cost per seat mile. Simply put, a long, thin light airplane will cause less boom than a heavy wide plane. But a long thin airplane is precisely what the airlines do not want. It is tougher to land and will carry fewer passengers, two solid anticommercial properties. Withington says the airlines, though concerned about the boom, “have not given us any trade factors" — things they would give up to reduce the boom. And TWA’s Rummel concedes: “There’s little room for trade-offs. The only way I know to get rid of the boom completely is to fly subsonically.”

To fly subsonically, of course, the airlines don’t need to spend $40 million for an SST. Along with Boeing and the FAA, the airlines can bide their time on the boom issue, knowing full well that once the SST is flying they will have a powerful foot in the door leading to unlimited flights. After all, who will then be able to clip the wings of a $4.5 billion bird nested by the government and carefully raised by one of the country’s biggest industries?

Stephen Shepard