# Supersonic Flight Integration

This case reviews the Challenge of Integrating Supersonic Flight into American Airspace. It is the collaborative work of Alexander Merker and Farida Ibrahim, graduate students enrolled in George Mason University's Transportation Policy, Operations, and Logistics Program at the time of writing. The following casebook explores the key actors, policy challenges, and history associated with supersonic commercial flight in the context of its potential reintegration into America's national airspace. It was produced as an assignment for George Mason University's Introduction to Transportation Systems graduate course, taught by Dr. Jonathan Gifford.

## Summary

In the early 2010s, interest in commercial supersonic air transport (SST) was renewed as advances in technology and an increasing demand for private and business air travel created a market niche for faster and longer-range aircraft. Supersonic air travel, that which exceeds the speed of sound, offers considerable speed advantages over subsonic flight. The Concorde, a first-generation supersonic airliner, completed air travel to London in only 2 hours, a third of the time its subsonic competitors took to complete the journey. The speed advantage of supersonic aircraft is a strong selling point in the private and business aviation market, where time-savings are a principal reason for ownership.
However, allowing supersonic aircraft to fly at their intended speeds in American airspace poses the same challenges it did over half a century ago when the first wave of supersonic airliners was in active development. The most significant regulatory barrier to supersonic aircraft is a Federal Aviation Administration ban on overland supersonic flight by civil aircraft in American airspace, which was enacted during the first wave of supersonic airliners in 1973. This ban and the public perceptions behind it remain a barrier to integration of such air travel into American airspace, with additional concerns regarding the environmental impact of the pollution generated by these aircraft contributing to public perception issues.

## Annotated List of Actors
### Aerospace Manufacturers

* Boom Technology
* Aerion Supersonic
* Spike Aerospace
* The Boeing Company
* Lockheed Martin

### Federal Aviation Administration

* Responsible for the regulation and oversight of airspace in the United States, the FAA establishes rules relating to supersonic flight in American airspace

### National Aeronautics and Space Administration

* NASA provides research into the effects of supersonic flight, in addition to developing sonic boom dampening technologies

### Environmental Groups

* The Anti-Concorde Project
* International Council on Clean Transport

### International Civil Aviation Organization

* United Nations body responsible for maintaining international standards for air travel

## Timeline of Events

1962: The British and French merge their development efforts and the Concorde Project begins
1963: Development of the Soviet Tu-144 begins
1967: The American SST Program selects the Boeing 2707 as its production design
1971: The American SST Program is cancelled
1973: The Federal Aviation Administration bans all civil aircraft from exceeding Mach 1 over land in American airspace
1975: The Tu-144 enters regularly scheduled service
1976: Concord begins regularly scheduled service
1983: The Tu-144 is retired from service
2003: British Airways and Air France retire the Concorde
2006: NASA begins its Quiet Spike sonic boom mitigation test program
2018: NASA begins construction of the QueSST Supersonic Demonstrator
2018: The Federal Aviation Administration (FAA) implements the Reauthorization act of 2018 which grants the Federal Aviation Administration (FAA) the power and authority to establish new federal and international policies to regulate and certify safe and efficient civil supersonic aircraft operations.
2020: Expected first flight of the Boom Technologies XB-1 Supersonic Demonstrator
2021: Expected first flight of NASA’s X-59 QueSST Supersonic Demonstrator
2023: Intended date of first flight for the Aerion AS-2 Supersonic Business Jet

## Maps of Locations

American Airspace Map
A Map of Concorde's Flight Path

## Policy Issues
### Noise Concerns

The primary regulatory concern involving supersonic aircraft is their trademark sonic boom. The sonic boom can be defined as “a shock wave of pressure created by compression of sound waves as the air is displaced by the air-frame traveling at or above Mach 1”. This shock wave of pressure results in a large ‘boom’ that are often compared to the clap of thunder. It is for this reason, that public pressure on the federal government was high in regards to the sonic booms created by aircraft travelling faster than Mach 1. The public skepticism surrounding supersonic flight was fueled by the belief that supersonic aircraft would be detrimental to public health and damaging to property. As a result, the federal government amended the existing Federal Aviation Act of 1958 to include a section that gave the Federal Aviation Authority (FAA) the capacity to extend already set noise standards of civil subsonic aircraft to supersonic civil airliners. As a result, the Control and Abatement of Aircraft Noise and Sonic Boom Act of 1968 was implemented. However, in 1973 the Federal Aviation Authority issued a ban on all civil air travel exceeding the sound barrier (Mach 1) over land in American airspace. To date, this ban remains the largest policy barrier for commercial supersonic aircraft in the United States. This is largely because it limits the capacity of supersonic airliners to service a large surface area and to expand its routes.
Studies into the subject of the sonic boom and the impact on health and property have yielded a an uncertain measurement of the impact of sonic boom pressure shock waves on the general population. As far back as the 1950s, studies have found that the impact of sonic booms is heavily dependent on factors such as aircraft altitude, atmospheric conditions and body shape. The most physical aspect of sonic booms, its characteristic pressure shock wave, was found by NASA to have been at a measurement 1.94 psf for the Concorde under normal flight conditions. This is at the cusp of the 2-5psf, what NASA categorizes as “Rare minor damage”, and above the 1.0 psf where public reaction is seen. However, the perceived impact of sonic boom in the form of shattered windows and other structural damage, has not been found to occur below 11 psf.
However, the opposing opinions on the effects of the supersonic aircraft have led to numerous debates between policy makers and supersonic flight proponents. This has resulted in continued dialogue between supersonic aircraft manufacturers and government agencies, such as the International Civil Aviation Organization (ICAO). Since the ban in 1973, stakeholders within the aerospace industry and NASA have worked to develop a better understanding of sonic boom and solutions for mitigation. Examples of this include NASA's Quiet Spike test bed.
With the resurgence of interest in supersonic transport technology, a renewed effort against the technology has emerged as well. In a series of announcements, the FAA pledged to acknowledge the technological differences between supersonic and subsonic aircraft and take it into consideration when assessing noise requirements. This was a significant achievement for the technology, showing both maturity in sonic boom mitigation developments, as well as changing perspectives on its impacts.
So far, dialogue between supersonic aviation and policy makers have remained open and productive as agencies such as the FAA have expressed willingness to modify current policies if supersonic airliners are able to achieve a sound level comparable to that of their subsonic counterparts. This signifies a shift in trends among policy makers as the FAA has shown willingness to revisit the issue and possibly lift the ban if provided with adequate research to support the stance that supersonic airliners will not be damaging to physical property, the environment, or the human body.
In 2019, the International Council on Clean Transport, an environmental advocacy organization focusing on transportation, produced a report outlining the potential environmental impacts of this technology under current fleet projections made my potential manufacturers. This report concluded that regions under the most traveled supersonic flight paths might experience sonic booms up to 200 times a day. The United States, United Kingdom and United Arab Emirates were expected to be the most traversed of all counties in this projected scenario for 2035.
Research into this topic continues at the same time NASA and the FAA work towards re-defining the standards for overland supersonic flight and an end to the ban on such air travel. One of the goals of NASA’s X-59 supersonic technology demonstrator is to build a supersonic aircraft that produces a reduced overland sonic boom. As a result, the X-59 has been marketed as a quieter supersonic aircraft with a mission to elicit public feedback on the impact of the modified produced for the purposes of reopening U.S. airspace to supersonic flight.

### Environmental Concerns

Rising concerns over climate change have resulted in an increasingly environmentally conscious society. As a result, environmental groups stand in opposition to the reintegration of supersonic transports into the national airspace. In addition to concerns over the impact of sonic booms, another concern for environmental groups are the emissions created by these aircraft which could potentially deplete the stratospheric ozone layer.
A 1966 scientific study by the American National Academy of Sciences confirmed that exhaust emissions released from supersonic jetliners are harmful to the stratosphere and could contribute to climate change. The research showed that “a five-fold increase in the amount of water vapor would lead to a two degree Celsius increase in surface temperatures”. A 2019 study on the carbon emissions impact of supersonic commercial aviation found that it would contribute to a substantial increase in such emissions.
In addition, a 1972 report by future Nobel Laureate Paul Crutzen, also found that nitrous oxide emissions from supersonic transport engines might have a significant impact on ozone depletion. This study was used as the basis for environmental agreements made by anti-SST organizations such as the Anti-Concord Project. Crutzen's work on ozone depletion would eventually lead to research which was crucial to the understanding of the human influence on climate change, for which he won a Nobel Prize.
More recently, a 2019 ICCT report on the environmental impacts of supersonic commercial aviation found that it would contribute to a substantial increase in carbon emissions. The study determined that a hypothetical global fleet of 2000 supersonic aircraft (as proposed by proponents of the technology) would emit a carbon footprint equivalent to 59% of the combined fleets of all American air carriers in 2017.
The issue of carbon footprint is a growing area of concern for the technology, as governments and airlines take increasingly aggressive measures to reduce carbon emissions in air travel. In 216, the United Nations body responsible for international aviation standards, The International Civil Aviation Organization, set in place a carbon emissions reduction program for international air travel. These strict standards are likely to conflict with the reintegration of commercial supersonic aircraft, though developers of the technology like Boom Technologies have claimed that their use of bio fuels over kerosene will have an mitigating effect on their carbon emissions, with its XB-1 test aircraft being "..history’s first zero net carbon footprint on a supersonic flight,".

## Narrative of the Case
### The First Wave of SST Development

In the early 1960s, airlines and aerospace manufacturers believed that the future of air travel would be through supersonic aircraft. Seeking to gain an advantage in an advantage for both their manufacturers and airlines, the United Kingdom, France, Soviet Union and the United States invested in programs to develop and produce supersonic airliners. The United Kingdom and France quickly merged their efforts, developing a partnership to build the Anglo-French Concorde. The United States, with a large manufacturing base to draw upon, selected two competing designs for further government investment in what was known simply as the SST Program. The Soviets utilized their Tupolev design bureau to develop their supersonic transport, the Tu-144.
In 1964 the Federal Aviation Administration (FAA) authorized a series of tests flights to be carried out in Oklahoma City. The purpose of these tests were to measure the effects of supersonic booms on the environment and also what physical effects it would have on civilians on the ground. These experiments were controversial as it was during this phase, that residents concentrated within these areas began to raise concerns about the loudness of supersonic engines and the damage it was doing to their property. Many people submitted claims to the government requesting compensation for broken windows, cracked tiles and other damage to physical property. In addition, there were also numerous complaints regarding the noise levels and the associated thunder claps. These experiences contributed heavily to the formation of public opinion as the experiences of individuals within this city continued to spread across the United States influencing the ideas and opinions about supersonic flight. By 1966, The Anti-Concorde project was formed to counterbalance the claims of the aerospace industry about the technical and economic viability of the Concorde program. This created the opportunity for people who shared similar views, to rally together collectively bargain against the Concorde. It became one of the most predominant groups in opposition to supersonic air travel, as it assembled a group of experts to publish information regarding the extensive fuel consumption, and sonic booms that would result from supersonic airliners. The project would also publicize the facts about the economics of Concorde; that the plane could not be operated at a profit, and that the research and development costs, funded entirely with taxpayer's money, would never be recovered. The anti-Concorde project used this information to lobby against the aerospace industry to end all supersonic transport projects on economic and environmental grounds.
Facing both intense scrutiny for its environmental impacts and a transition by American air carriers to high-capacity subsonic aircraft, the United States cancelled its supersonic airliner program (SST) in 1971 before a prototype could fly. Boeing, the winner of the design competition for the SST program, was forced to lay off more than 60,000 employees as a result of the program’s cancellation. Shortly after the end of the SST Program, the Federal Aviation Administration would ban all overland supersonic flight by civil (non-federal) aircraft in 1973. The ban remains in place to this day.
The Anglo-French Concorde and Soviet Tu-144 projects continued despite challenges in public perception and airline economics. The Concorde and Tu-144 entered full commercial service in the mid-1970s, achieving the project goals. However, they still faced challenges. The Tu-144, which suffered a fatal crash on the world stage at the 1971 Paris Airshow, was found to be ill-suited for passenger air travel due to high internal noise levels and serious reliability issues. As a result, the Soviet Union retired the Tu-144 from commercial airline service less than a decade later in 1983.
After the retirement of the Tu-144, the Anglo-French Concorde maintained its status as the only active commercial supersonic aircraft despite challenges involving public perception and the economic viability of the project. The Concorde fared far better than the Tu-144, remaining in service until 2003. Serving the national flagship carriers of the United Kingdom (British Airways) and France (Air France), fourteen Concorde's provided transatlantic supersonic air travel between their national capitols and New York City. The Concorde was not the commercial success it was intended to be though. The economics of operating the fuel inefficient aircraft, which sat only 100 passengers, were compounded by bans on overland supersonic travel that eliminated all but one destination outside of Europe. In comparison, the Concorde’s subsonic competitor Boeing 747 sat 660 passengers and consumed half the amount of aviation fuel during an equivalent flight between New York and London. By the 2000s, increasing costs of fuel and maintenance led to the retirement of the aircraft from both fleets, bringing an end to supersonic commercial air travel.

### Continuing Investment in SST Technology

Despite the cancellation of the American SST Program, supersonic aircraft testing and research was not abandoned entirely in the United States. NASA continued to study potential evolutions of the design and made notable contributions to the cause by offering potential solutions to the design challenges that led to the cancellation of the SST. NASA, through its research, continued to influence supersonic transport development and remained a fundamental contributor to the study of supersonic flight. This included a partnership with its Russian counterparts in 1996 for continued supersonic transport development, retrofitting a Tu-144 for test flights that were conducted through 1999. More recently, NASA studied supersonic boom mitigation through Quiet Spike Program, which mounted a modified nosecone to an F-15B aircraft to test experimental structural solutions to the issue.

### The Second Wave of SST Development

Currently, in response to renewed business interest in such aircraft, NASA is in the final development stages of the X-59 Quiet Supersonic Transport experiment aircraft that will demonstrate new technologies and design methods for civilian supersonic aircraft. The overall goal of this program is to develop sonic boom dampening technologies that will allow for a return to overland supersonic travel.
Outside of government initiatives into this technology, private industry has taken a strong interest in the prospects of supersonic air travel for private and business aviation. In these markets, where time savings are the commodity being purchased, the benefits of supersonic air travel are clear over current aircraft. The current fastest business aircraft, the Cessna Citation X+, has a top speed of Mach 0.935, just below the sound barrier. Aerospace startups Boom Technologies and Aerion Supersonic believe that their in-development supersonic business jets will fill this market niche.
The first tests of new supersonic transport demonstrator aircraft are expected to take place in the early 2020s. The NASA developed and Lockheed Martin produced X-59 is scheduled for its first flights in 2021, while the Boom Technologies XB-1 is expected to fly in 2020. Meanwhile, Aerion Supersonic intends to produce and fly its AS-2 supersonic business jet by 2023, forgoing the process of developing a demonstrator entirely. All of these designs, with the exception of the X-59, will depend upon a repeal of the overland supersonic flight ban before they can enter the market.
Federal regulators are presently optimistic of a near-future repeal of the supersonic test ban. The FAA is currently in the process of developing standards for overland supersonic flight, though they would not outright repeal the ban. This rule-making process would create a noise certification process through which manufacturers would need to seek approval for designs under yet to be determined noise standards. The data collected through the X-59 program will be used in the development of these standards. Additionally, the FAA is working to develop a streamlined approval process for supersonic flight authorization, which would allow pilots to legally fly pass the speed of sound. The FAA expects that these two regulatory changes would allow for commercial supersonic flight without repealing the overland ban, instead providing a process through explicit authorization for such flight activities. This is, in essence, an indirect repeal of the overland supersonic ban.
Outside of the United States, there is at least one other program to develop a supersonic transport aircraft. In Japan, the Next Generation Supersonic Transport program has been in active development since 2006. This project, financed by the Japan Aerospace Exploration Agency (JAXA), intends to ultimately produce a supersonic aircraft which will seat up to 50 passengers. If this program were to succeed in producing a commercial aircraft by 2030, it would almost certainly fly through American airspace.

## Lessons learned

Going forward, it is fundamental to acknowledge the importance of public perception and its influence on guiding public policy. The regulatory obstacles were due in large part due to public perceptions of the impact of supersonic aircraft, many of which did not align with research into the subject. A barrier to the reintegration of supersonic flight into American air space remains the regulatory policies that prohibit supersonic airliners from flying over land. These existing regulatory policies hinder the success of supersonic airliners by limiting their hide speed transit to specific trans-oceanic routes. It is evident from past experience that without public approval supersonic air travel would have limited mainstream success. This case study is an excellent example of how the development of technologies can be affected by politics and public discourse. In the instance of this technology, a stagnation in innovation was not the reason for its demise, but rather the misinformed opinions of the voting public that resulted in regulatory action. At the moment, this regulatory action remains a barrier for the revival of this technology, and the public perceptions which led to it have forced innovators to respond to these beliefs with investments in noise reduction technologies.
In addition to the regulatory barriers that remain in place, the process of removing such barriers will likely run afoul of environmental groups and those ambivalent about aircraft noise and the effects of sonic booms. In the 1960s, the chorus of concerns for both emissions impacts and noise issues played a very prominent role in the creation of the regulatory barriers that exist today. Both manufacturers and users of these aircraft will need to address these concerns as the make their case for an indirect deregulation of the FAA’s overland supersonic flight restrictions. These issues are already present in the national conversation for conventional commercial aviation, with “Flight Shaming” over the emissions of air travel currently gaining popularity in Europe and noise complaints surging as the FAA implements its “NextGen” air traffic management system.
While both technical and public perception barriers exist for the reintegration of these aircraft into the national airspace, it is clear that the FAA and Department of Transportation are in support of loosening restrictions. Though there is a groundswell of investment of these aircraft, and a perceived business case for their revival, eliminating regulatory barriers is the most fundamental requirement for their viability in the American market. The clear interest shown by the FAA and Department of Transportation are therefore crucial indicators of the likelihood of success in both reintegrating these aircraft into U.S. airspace, as well as their business viability. Reintegration will of course also rely on continued mitigation efforts in noise and environmental impact, two of the two biggest points of contention for the technology's detractors. As covered in this case study, both government and industry are in the process of developing mitigation techniques for both, and this will likely be one the of biggest cases for loosening restrictions and successful reintegration. Therefore, it can be assessed that there is a high likelihood that reintegration efforts will be successful and commercial supersonic aircraft will fly in American skies in due time.

## Discussion Questions

* To what extent should public perceptions of technologies be taken into account by policy makers?
* How much should environmental concerns be weighed against the potential economic benefits of a transportation technology?
* Are there any other examples of technologies whose development was curtailed due to environmental concerns?
* Given the evidence put forth in this case book, do you believe the overland supersonic flight ban should be repealed?

## Assigned Readings

GMU Mercatus Center: Make America Boom Again: How to Bring Back Supersonic Transport (2016, 39 Pages)
The Heritage Foundation: It’s Time to Let Supersonic Flight Soar Again (2018, Web)
Aerospace America: Supersonic’s not-so-super emissions (2019, Web)
Congressional Research Service: Supersonic Passenger Flights (2018, 18 Pages)
International Council on Clean Transport: Noise and climate impacts of an unconstrained commercial supersonic network (2019, 15 Pages)

## References

* ↑ https://fas.org/sgp/crs/misc/R45404.pdf
* ↑ Controlling aircraft noise and sonic boom, 49 USCS § 44715 (2011)
* ↑ Hadhazy, A. (2019, October). Supersonic’s not-so-super emissions | Aerospace America. Aerospace America. Retrieved from https://aerospaceamerica.aiaa.org/features/supersonics-not-so-super-emissions/
* ↑ Elias, B. (2018). Supersonic Passenger Flights. In crsreports.gov (pp. 8). Retrieved from Congressional Research Service website: https://crsreports.congress.gov/product/pdf/R/R45404
* ↑ Elias, B. (2018). Supersonic Passenger Flights. In crsreports.gov (pp.12). Retrieved from Congressional Research Service website: https://crsreports.congress.gov/product/pdf/R/R45404
* 1 2 National Aeronautics and Space Administration. (2011). NASA Armstrong Fact Sheet: Sonic Booms. Retrieved October 30, 2019, from nasa.gov website: https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-016-DFRC.html
* 1 2 National Aeronautics and Space Administration. “Quiet Spike.” NASA, 2011, www.nasa.gov/centers/dryden/multimedia/imagegallery/Quiet_Spike/Quiet_Spike_proj_desc.html. Accessed 30 Oct. 2019.
* ↑ Levin, A. (2019, June 17). FAA Will Propose Streamlining Supersonic Flight-Test Approvals. Retrieved November 4, 2019, from Bloomberg.com website: https://www.bloomberg.com/news/articles/2019-06-17/faa-will-propose-streamlining-supersonic-flight-test-approvals ‌
* ↑ Elias, B. (2018). Supersonic Passenger Flights. In crsreports.gov (pp.13). Retrieved from Congressional Research Service website: https://crsreports.congress.gov/product/pdf/R/R45404
* ↑ Rutherford, D., Graver, B., & Chen, C. (2019). Noise and climate impacts of an unconstrained commercial supersonic network. Retrieved from International Council on Clean Transportation website: https://theicct.org/sites/default/files/publications/Supersonic_Impact_Working_Paper_20190130.pdf
* ↑ Reid, D. (2018, September 24). Lawmakers pave the way for the return of supersonic flight. Retrieved October 30, 2019, from CNBC website: https://www.cnbc.com/2018/09/24/us-lawmakers-are-all-set-to-speed-the-return-of-supersonic-flight.html
* ↑ National Aeronautics and Space Administration. (2011a). Low-Boom Flight Demonstration: The Mission. Retrieved October 30, 2019, from nasa.gov website: https://www.nasa.gov/mission_pages/lowboom/mission
* ↑ Drake, F., & Purvis, M. (2001). The Effect of Supersonic Transports on the Global Environment: A Debate Revisited. Science, Technology & Human Values, 26(4), 508. https://doi.org/10.1177/016224390102600406
* ↑ Drake, F., & Purvis, M. (2001). The Effect of Supersonic Transports on the Global Environment: A Debate Revisited. Science, Technology & Human Values, 26(4), 508. https://doi.org/10.1177/016224390102600406
* ↑ Rutherford, D., Graver, B., & Chen, C. (2019). Noise and climate impacts of an unconstrained commercial supersonic network. Retrieved from International Council on Clean Transportation website: https://theicct.org/sites/default/files/publications/Supersonic_Impact_Working_Paper_20190130.pdf
* ↑ Crutzen, P. (1972). SST’s: A Threat to the Earth’s Ozone Shield. Ambio, 1(2), 41–51. Retrieved from http://www.jstor.org/stable/4311946
* 1 2 The Anti-Concorde Project. (1972). Concrode - 1962-1972: Is it Already Obsolete? Retrieved from https://upload.wikimedia.org/wikipedia/commons/6/61/ACPTimes.jpg
* ↑ “The Nobel Prize in Chemistry 1995: Paul J. Crutzen.” NobelPrize.Org, The Nobel Prize, www.nobelprize.org/prizes/chemistry/1995/crutzen/facts/. Accessed 30 Oct. 2019.
* ↑ Rutherford, D., Graver, B., & Chen, C. (2019). Noise and climate impacts of an unconstrained commercial supersonic network. Retrieved from International Council on Clean Transportation website: https://theicct.org/sites/default/files/publications/Supersonic_Impact_Working_Paper_20190130.pdf
* ↑ Corsia: The UN’s plan to ‘offset’ growth in aviation emissions after 2020. (2019, February 4). Retrieved October 30, 2019, from Carbon Brief website: https://www.carbonbrief.org/corsia-un-plan-to-offset-growth-in-aviation-emissions-after-2020
* ↑ Jasper, C., & Johnson, J. (2019, June 28). The New Era of Supersonic Travel May End Before It Even Begins. Retrieved November 4, 2019, from Bloomberg.com website: https://www.bloomberg.com/news/articles/2019-06-28/the-new-era-of-supersonic-travel-may-end-before-it-even-begins ‌
* ↑ Who Will Win the Supersonic Race?; At stake in the worldwide drive to be first with Mach 2‐plus passenger planes is national prestige. But before the jets fly, some hard questions must be answered. (1964, August 23). The New York Times. Retrieved from https://www.nytimes.com/1964/08/23/archives/who-will-win-the-supersonic-race-at-stake-in-the-worldwide-drive-to.html
* ↑ Klein, C. (2016, January 21). The Cold War Race to Build the Concorde. Retrieved October 30, 2019, from history.com website: https://www.history.com/news/the-cold-war-race-to-build-the-concorde
* ↑ Dowling, S. (2016). The American Concordes that never flew. Retrieved October 30, 2019, from Bbc.com website: https://www.bbc.com/future/article/20160321-the-american-concordes-that-never-flew
* ↑ Beresnevicius, R. (2018, December 5). The Lost Brother of Concorde: The story of Tupolev Tu-144. Retrieved October 30, 2019, from Aerotime.aero website: https://www.aerotime.aero/rytis.beresnevicius/23029-lost-brother-of-concorde-story-tupolev-tu-144
* ↑ Borsky, P. (1965). Community Reactions to Sonic Booms (National Opinion Research Center, Ed.). Retrieved from University of Chicago website: http://www.norc.org/PDFs/publications/NORCRpt_101.pdf
* ↑ Borsky, P. (1965). Community Reactions to Sonic Booms (National Opinion Research Center, Ed.). Retrieved from University of Chicago website: http://www.norc.org/PDFs/publications/NORCRpt_101.pdf
* ↑ The Anti-Concorde Project. (1972). Concrode - 1962-1972: Is it Already Obsolete? Retrieved from https://upload.wikimedia.org/wikipedia/commons/6/61/ACPTimes.jpg
* ↑ Dowling, S. (2016). The American Concordes that never flew. Retrieved October 30, 2019, from Bbc.com website: https://www.bbc.com/future/article/20160321-the-american-concordes-that-never-flew
* ↑ Conway, E. (2008). High-speed dreams : NASA and the technopolitics of supersonic transportation, 1945-1999. Baltimore, Md: Johns Hopkins Univ Press.
* ↑ Supersonic Civilian Flights Over U.S. Are Outlawed. (1973, March 28). The New York Times. Retrieved from https://www.nytimes.com/1973/03/28/archives/supersonic-civilianflights-over-us-are-outlawed.html
* ↑ Controlling aircraft noise and sonic boom, 49 USCS § 44715 (2011)
* ↑ Beresnevicius, R. (2018, December 5). The Lost Brother of Concorde: The story of Tupolev Tu-144. Retrieved October 30, 2019, from Aerotime.aero website: https://www.aerotime.aero/rytis.beresnevicius/23029-lost-brother-of-concorde-story-tupolev-tu-144
* ↑ Slotnick, D. (2019, October 7). The history of the Concorde supersonic jet - Business Insider. Retrieved October 30, 2019, from Business Insider website: https://www.businessinsider.com/concorde-supersonic-jet-history-2018-10
* ↑ Slutsken, H. (2019, March 2). What it was really like to fly on Concorde. Retrieved October 30, 2019, from CNN Travel website: https://www.cnn.com/travel/article/concorde-flying-what-was-it-like/index.html
* ↑ Bramson, D. (2015, July). The Concorde: A Supersonic Airplane Too Advanced to Survive. Retrieved October 30, 2019, from The Atlantic website: https://www.theatlantic.com/technology/archive/2015/07/supersonic-airplanes-concorde/396698/
* ↑ The Boeing Company. (1989). NASA Contractor Report 4233: High-Speed Civil Transport Study. In nasa.gov. Retrieved from National Aeronautics and Space Administration website: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890018277.pdf
* ↑ National Aeronautics and Space Administration. (2011b). NASA Armstrong Fact Sheet: Sonic Booms. Retrieved October 30, 2019, from nasa.gov website: https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-016-DFRC.html
* ↑ NASA’s Supersonic X-59 QueSST Coming Together at Famed Factory. (2019). Retrieved from NASA website: https://www.nasa.gov/aero/nasa-supersonic-x59-quesst-coming-together-at-famed-factory
* ↑ Trautvetter, C. (2018, June 26). Textron To Cease Production of Cessna Citation X+. Retrieved October 30, 2019, from AIN Online website: https://www.ainonline.com/aviation-news/business-aviation/2018-06-26/textron-cease-production-cessna-citation-x
* ↑ Falcus, M. (2019, April 5). What supersonic travel means for you. Retrieved October 30, 2019, from cnn.com website: https://www.cnn.com/travel/article/supersonic-travel/index.html
* ↑ National Aeronautics and Space Administration. (2011a). Low-Boom Flight Demonstration: The Mission. Retrieved October 30, 2019, from nasa.gov website: https://www.nasa.gov/mission_pages/lowboom/mission
* ↑ Waldron, G. (2019, June 19). PARIS: Boom XB-1 schedule slips, while JAL eyes Overture. Retrieved October 30, 2019, from Flightglobal.com website: https://www.flightglobal.com/news/articles/paris-boom-xb-1-schedule-slips-while-jal-eyes-ove-459129/
* ↑ Aerotime.aero. (2019, February 4). Boom, Aerion & Spike head-to-head in supersonic jet race. Retrieved October 30, 2019, from Aerotime.aero website: https://www.aerotime.aero/aerotime.team/22308-boom-aerion-spike-head-to-head-in-supersonic-jet-race?page=2
* ↑ Federal Aviation Administration. (2019). Fact Sheet – Supersonic Flight. Retrieved September 17, 2019, from Faa.gov website: https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=22754
* ↑ Federal Aviation Administration. (2019). Fact Sheet – Supersonic Flight. Retrieved September 17, 2019, from Faa.gov website: https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=22754
* ↑ Ryall, J. (2016, July 23). Supersonic: Japan’s space agency is working on ‘son of Concorde.’ Retrieved October 30, 2019, from South China Morning Post website: https://www.scmp.com/news/asia/east-asia/article/1993690/supersonic-japans-space-agency-working-son-concorde
* ↑ Goldstein, M. (2019, June 5). Does Flight-Shaming Over Climate Change Pose An Existential Threat To Airlines? Forbes. Retrieved from https://www.forbes.com/sites/michaelgoldstein/2019/06/04/does-flight-shaming-over-climate-change-pose-an-existential-threat-to-airlines/#1d2459ea3cfc
* ↑ Aratani, L. (2019, June 25). House passes amendment to prioritize efforts to combat airplane, helicopter noise. The Washington Post. Retrieved from https://www.washingtonpost.com/transportation/2019/06/25/house-passes-amendment-prioritize-efforts-combat-airplane-helicopter-noise/