	Introduction

Four decades have passed since the first trans-oceanic supersonic passenger flight took off from London Heathrow Airport in 1976. Several U.S. startup companies are now developing supersonic commercial and business jets. In subsonic flight, sound waves may be emitted in all directions. More than 2.5 million passengers flew supersonically before Concorde was taken out of service in 2003. But it was not financially successful. Future Aircraft Development

The revival of interest in supersonic aircraft is the result of technological advances in materials, airframe and engine designs, and aircraft manufacturing that would be able to give the aircraft longer range through improved fuel efficiency and substantial weight savings with advanced composites and aerodynamics. At present, there are no agreed-upon international standards for next-generation supersonic aircraft. The International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection is presently seeking to develop international noise and emissions standards for future supersonic aircraft. Noise standards in the United States and other countries, dating to the early years of the Concorde, prohibit supersonic flight over land. Aircraft Certification Timeline

The FAA Reauthorization Act of 2018 directs FAA to take a leadership role in creating federal and international policies, regulations, and standards to certify safe and efficient civil supersonic aircraft operations within U.S. airspace. The legislation requires FAA to consult with industry stakeholders on noise-certification issues, including operational differences between subsonic and supersonic aircraft. It further requires FAA to issue an NPRM, no later than March 31, 2020, to develop noise standards for sonic boom over the United States and for takeoff and landing and noise test requirements applicable to civil supersonic aircraft, and to publish the final rule within 18 months after the public comment period closes. Furthermore, beginning December 31, 2020, and every two years thereafter, FAA would be required to review available aircraft noise and performance measurements to determine if federal regulations should be amended to remove the current ban on civil supersonic flight over land. However, language in P.L. However, as it turned out, no Concorde aircraft were produced after 1979. Many recent commercial jet models already meet the Stage 5 requirements, and in general, the subsonic commercial aircraft fleet is considered to be 75% quieter overall than aircraft produced in the 1970s. Further, FAA stated that "noise standards for supersonic operation will be developed as the unique operational flight characteristics of supersonic designs become known and the noise impacts of supersonic flight are shown to be acceptable."
It has been over 40 years since British Airways' first Concorde passenger flight took off in 1976. So far the Concorde is the only commercial supersonic passenger aircraft to travel at more than twice the speed of sound. It was a technological accomplishment but not a commercial success. In 2003, all Concorde aircraft were taken out of service.
Recent years have seen a revival of interest in supersonic aircraft. Several startup companies are developing new supersonic commercial and business jets, hoping technological advances in materials, design, and engine efficiency will make it possible to produce commercially viable aircraft.
The main regulatory issues related to supersonic flight remain unchanged from the Concorde era: limiting ground-level noise during subsonic flight and sonic booms during supersonic flight. Aircraft noise standards have become much stricter since the Concorde entered service, and the commercial aircraft fleet is considered to be 75% quieter overall than during the 1970s. However, some of the technical approaches used to reduce noise during subsonic flight may hinder efforts to reduce the magnitude of sonic booms in future supersonic aircraft.
In the United States, the FAA Reauthorization Act of 2018 (P.L. 115-254) directs the Federal Aviation Administration (FAA) to take a leadership role in creating federal and international policies, regulations, and standards to certify safe and efficient civil supersonic aircraft operations. It requires FAA to consult with industry stakeholders on noise-certification issues, including operational differences between subsonic and supersonic aircraft. It also requires FAA to develop and issue noise standards for sonic boom over the United States and for takeoff and landing and noise test requirements applicable to civil supersonic aircraft. Furthermore, beginning December 31, 2020, and every two years thereafter, FAA will be required to review available aircraft noise and performance measurements to determine if federal regulations should be amended to remove the current ban on civil supersonic flight over land.
Since new supersonic aircraft are expected to operate internationally, the lack of agreed-upon international standards or agreements is likely to hinder production as well as operations. FAA is already engaged with the International Civil Aviation Organization (ICAO) to develop certification standards for future supersonic aircraft, but this process to produce an international standard may not be completed until 2025. In addition, the United States and other countries prohibit supersonic flights over land except in limited circumstances, and changes in those restrictions may be necessary for supersonic aircraft to be commercially viable.