No boom at speeds up to Mach 1.2

Since the concorde era,

in fact because of the Concorde, supersonic flight over the U.S. has been prohibited by an act of Congress. Above Mach 1 any aircraft will create a pressure wave perceived as a sonic boom. Some can be quite loud. Others are less audible. Larger supersonic aircraft tend to produce louder booms. New technologies are emerging to muffle booms. As yet, there is no U.S. or international standard for an acceptably quiet supersonic boom.

International standards, however, are different. These standards come from the International Civil Aviation Organization (ICAO), a United Nations organization. ICAO permits supersonic flight over land so long as no disturbance is created at the ground. This regulatory flexibility opens an interesting avenue to legal overland supersonic flight in most areas of the world.

The physics of sonic booms are such that not all booms reach the ground. This phenomenon is known as "Mach cutoff." Mach cutoff is determined by atmospheric conditions, principally temperature and winds. Modern onboard avionics can use atmospheric data to calculate a supersonic speed that would cause the boom to “refract,” or bounce upward at 5,000 feet above the ground. In the AS2, this speed would vary from Mach 1.1 to as high as Mach 1.2. So, in many parts of the world, the AS2 could fly overland at supersonic speeds.

At speeds just above Mach 1, sonic booms do not reach the ground. The AS2 can use this "Mach cutoff" phenomenon to fly supersonically over populated areas.

At Mach 1.2, the AS2 would be flying as much as 50 percent faster than today’s jets. Once the AS2 is in service and demonstrating boomless overland flight due to Mach cutoff, it is possible the U.S. would bring its regulations into conformity with the global standard. However, the Aerion business case assumes no change in U.S. law or regulation.