National Geographic : 1969 Sep
The supersonics, however, are not without their critics. Much of the criticism centers around the sonic boom-a cone-shaped wave of air pressure that trails behind the aircraft during supersonic flight. It can cause annoy ance to people and structural damage to buildings within its range. Engineers are working on designs and devices to reduce the boom's effect, but no one knows yet whether they will be successful. If the problem remains insoluble, super sonic flight may be permitted only over water. 332 Airlines point out that, except in Russia and mainland China, 70 percent of today's air routes are over water, and another 20 percent probably could be rerouted, so the matter is not as serious as it would at first seem. Thus the SST, sonic boom or not, will make an important contribution to future travel, in the opinion of most experts. Former Secretary of Transportation Boyd made this predic tion: "I think the SST will become the major long-haul unit of personal transportation-I would guess by the late 1980's."