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While just the first step in a long process required before civil supersonic operations can become a reality, the U.S. FAA’s recently released notice of proposed rulemaking on special flight authorizations already is showing the complexities and difficulties of reversing the decades-long ban. The FAA in June issued a notice of proposed rulemaking (NPRM) to provide for a procedure to request authorization under Part 91 for supersonic flights over the U.S. for testing and development of aircraft. Current regulations prohibit all over-land supersonic civil flights in the U.S.
Released at the behest of the U.S. Congress, that NPRM is intended to provide a “user-friendly” application that consolidates requirements, such as specifics on flights, reasons speeds greater than Mach 1 would be necessary, reasons why the testing could not be accomplished over the ocean, and details on conditions to ensure that no measurable sonic boom overpressure will reach the surface.
This NPRM has been lauded by the industry as an important and necessary step forward to the development and eventual operation of a new generation of civil supersonic aircraft. Yet a the same time, those industry groups have expressed concerns ranging from the possibility that the NPRM establishes a de facto ban on supersonic testing to a call for further protections for other operators. And, the NPRM is already coalescing the beginning of significant opposition from a range of environmental groups.
From the industry standpoint, most recognize the need for rulemaking and the possibilities for a new generation of flight. “Breaking the sound barrier not only exemplifies the essence of flight, but its imminent routine occurrence in commercial and non-commercial flying also represents a new potential market in the aviation industry,” the Aircraft Owners and Pilots Association (AOPA) said in comments on the NPRM. “As the interest in this flight regime increases, so does the need for policies and procedures that integrate these emergent operators with existing general aviation flights in a safe and efficient manner.”
“The business aviation community is often an early adopter of new technologies, driving innovation and change. Members of this community are striving to be the first to market, and we are leading efforts at ICAO [the International Civil Aviation Organization] to develop international standards for supersonic transport,” NBAA added in its comments. “This proposed rule to modernize flight-test authorizations for supersonic aircraft is an important first step toward enabling the next generation of environmentally responsible supersonic aircraft.”
NBAA joined with manufacturing representatives including the General Aviation Manufacturers Association (GAMA) and the Aerospace Industries Association (AIA) in emphasizing the need for new supersonic aircraft designs to be environmentally responsible to be able to fulfill the vision of new possibilities for travel. “We are advocating for a modern regulatory framework that delivers a balance between protecting against significant impacts on people and the environment and fostering an ecosystem where new technologies can thrive,” GAMA and AIA said in joint comments.
To that end, all three associations agreed in two basic tenets: the FAA should prohibit routine flights at supersonic speeds over land until technologies provide for acceptable levels of noise exposure, and manufacturers need to incorporate technologies that minimize landing and takeoff noise.
On the first point, the associations stressed, “The industry has no intention of creating aircraft that cause loud sonic booms over populations, and it supports appropriate rules to prevent this from happening.” However, they also noted that technologies exist to enable supersonic speeds without an audible boom on the ground and added that NASA research will provide necessary data to support responsible supersonic speeds.
On the second tenet, the manufacturers acknowledged the differences in performance characteristics—and accompanying noise—in supersonic designs but pledged that manufacturers “are committed to ensuring these aircraft are no louder than aircraft that currently operate around airports today.” They pointed to the “huge advances” made in modern technology, estimating that the latest commercial aircraft models are 85 percent more fuel-efficient and 75 percent quieter than the first generation of jetliners. “We expect to see similar improvements in supersonic aircraft performance over time.”
These tenets were fully endorsed by manufacturers such as GE Aviation, the engine partner on Aerion’s AS2 supersonic business jet project. “Our responsibility goes beyond producing propulsion systems that power aircraft with acceptable noise levels, but that aircraft powered by our propulsion systems are compatible with the aviation industry’s ambitious carbon reduction goals,” GE Aviation added. “Manufacturers are already committed to producing the most fuel-efficient supersonic aircraft that are technologically feasible.”
The manufacturing community also stressed the need to be able to move forward with testing. “For manufacturers, testing at supersonic speeds will allow them to better understand the environmental impacts supersonic flight will have and inform decisions on the future design and operation of aircraft,” GAMA and AIA said.
However, at the same time, several manufacturers joined GAMA and AIA expressing concern that the NPRM, as written would serve as a barrier to development. Most of those commenters, also including GE Aviation, Aerion, and Boom, were particularly worried that the NPRM describes restrictive terms of “no sonic boom overpressure” and “no measurable sonic boom overpressure” as the implied standard for supersonic test flight over land. The associations called the terms “absolute prohibitions” and said they “would be unduly restrictive and one that an applicant would be unable to guarantee on a test flight.”
To achieve the intent of the NPRM, GAMA and AIA suggested that the FAA instead ensure that such flights would have no significant impacts on the environment or communities. The associations asked the FAA to use the same approach as used in other forms of transportation, including subsonic aircraft, under the National Environmental Policy Act.
“We believe that transportation impacts on communities and the environment should not be assessed differently because of the source of those impacts,” the associations said. “We believe that the sonic booms associated with a small number of supersonic test flights in an appropriate test area should not be considered as creating a significant impact on the environment.” The terms “no sonic boom overpressure” and “no measurable sonic boom overpressure” ignore that it is possible for a sonic boom to occur without it being audible on the ground, they added.
Aerion echoed the sentiment that “no measurable sonic boom overpressure” over land “would effectively create a ban on all supersonic flight” and agreed it should be replaced “with a reasonable standard based on currently available sonic boom prediction and control technology.” The Reno, Nevada-based developer of the AS2 further reiterated that the same standards should apply to other forms of transportation.
The overpressure measurement “goes far beyond what is required under the National Environmental Policy Act [NEPA]” and is unnecessary, added Boom Technology, a developer of a commercial passenger supersonic jet. “The FAA has the tools to determine whether such a condition is consistent with the level of environmental protection required.”
The manufacturing groups had several other specific concerns on the language from flexibility on testing sites, use of over-water testing, and stipulations on explaining why the tests could not be conducted over water, among others.
As for operators, AOPA had a different concern: ensuring safety and efficiency at lower altitudes. The FAA should consider how supersonic aircraft characteristics affect other aircraft; how see-and-avoid will take place; and the importance of the NEPA when adjudicating and approving applications, the association said.
“It is critical that both the wake characteristics of airframes and the requisite air traffic separation standards are identified so that, in conjunction with the efficiency impact, the disruption or cost to other operators can be accurately determined,” AOPA said. “It is crucial that the operation is both efficient and seamless.”
AOPA is particularly concerned that pilots operating under VFR above 10,000 feet msl might not have the ability to see and avoid supersonic aircraft flying at supersonic speeds. “Given that danger, we believe that the FAA should study whether subsonic speeds below Flight Level 180 (FL180) should be required,” the association said, adding that the FAA “should scrutinize any overland application for supersonic speeds below FL180 that do not include effective mitigations for see-and-avoid.”
AOPA pointed to higher VFR weather minimums above 10,000 feet msl put in place for Class E airspace because of the additional distance required to see and avoid aircraft with speeds above 250 knots. “These differences in basic VFR weather minimums highlight not only the important relationship between a pilot’s ability to conduct see-and-avoid but also illustrate why the 250-knot speed limit exists [below 10,000 feet in Class E airspace].”
Of particular concern is mitigations could be “one-sided,” the association added. "We are troubled that there could be situations in which pilots will be faced with having to completely relinquish their responsibility for themselves and their passengers’ safety to the pilot of another aircraft, especially one with whom they have no contact [visual or otherwise].”
While industry groups seek changes to the NPRM that would bolster the ability to access special authorizations and protection for other operations, environmental groups do not see a path forward at all. The Center for Biological Diversity (CBD) filed comments signed by 27 other public health and environmentalist groups that began with the headline "Prevent Devastating Harms from Super-Polluting Supersonic Aircraft."
The groups are not persuaded by assurances from the aviation community that they have no plans to recreate the Concorde and stated plans from at least GE Aviation to provide a Stage 5-compliant engine that can run on biofuel. “With existing technology, there is no way to advance ‘safe and efficient operation of supersonic aircraft.’ Supersonic aircraft would fuel the global climate crisis and threaten Americans with lasting damages from extreme air and noise pollution,” said the groups, which include organizations such as Friends of the Earth, Sierra Club, National Resources Defense Council, and Nurse Alliance of SEIU Healthcare.
CBD had filed a white paper on the emerging aircraft designs—acknowledging unknowns in designs and materials, and in Boom's case, engine—primarily making estimates off a three-view drawing on Boom's website, but found that, conservatively, the aircraft would be unable to meet noise and emissions standards.
The groups expressed concern supersonic operations will burn five to seven times the amount of fuel (on a per-passenger basis) as subsonic designs and international carbon dioxide emissions limits. “We are in a climate emergency. Given our limited carbon budget, limited time to act, and urgent need to slash greenhouse pollution from the aviation sector overall, allowing a new class of super-polluting aircraft to enter the sky would be madness. It is obviously inconsistent with the FAA’s obligations to protect public health and welfare,” they said.
Separately, CBD filed comments reiterating the warning of the environmental harm that could result from any testing and urging the FAA to impose a high test that involves significant environmental study for each application. “As the FAA grapples with the purported reemergence of civil supersonic aircraft, it must ensure that it takes the devastating environmental impact of these aircraft into account in all action it takes as a regulatory body.”
The center worries that the FAA is mischaracterizing the extent of its obligations under NEPA. That policy obligates agencies to take a “hard look” at environmental impacts before deciding whether to pursue a particular federal action, the center said, contending that each application for a special flight authorization would necessitate an environmental assessment (EA) and environmental impact statement (EIS).
It fears that the FAA believes an EA would fulfill its duties. An EA might help the FAA determine whether the application has a finding of no significant impact or, conversely, a significant impact that requires an EIS, CBD explained.
But the center believes that the proposal itself underscores the environmental harm posed by supersonic flight. “Because sonic boom, no matter how ‘quiet’ or insignificant, trails an aircraft in supersonic flight along its entire route, impacts are not limited to land surrounding airports,” the center said, adding, “Wildlife, domestic animals, and built structures and infrastructure are also affected by sonic boom. Exposure to aircraft noise over time is associated with increased risk of high blood pressure and heart disease for adults, and cognitive impairments in children.”
A conclusion requiring anything less than a full EIS would be inconsistent with science and 50 years of FAA policy, CBD added.
The FAA should use the strictest possible standard, as well as lessons learned from NextGen procedures implementation, added a residents group outside San Francisco that calls themselves the Sunnyvale/Cupertino Airplane Noise Group. “A high hurdle should be met in order to remove this supersonic flight ban, and these new supersonic aircraft should meet stringent airplane-noise and fuel-efficiency standards equivalent to newly manufactured subsonic aircraft,” the residents said.
Of chief concern was their experience of the implementation of NextGen procedures in the San Francisco Bay Area Metroplex. “Since the implementation of NextGen, our cities have experienced a problem with aircraft noise. The FAA should not compound this problem by adding supersonic aircraft to the mix while people across the country are still suffering from NextGen.”
They gave a number of recommendations, such as no audible sonic boom at ground level, the application of the same noise and fuel standards for subsonic and supersonic aircraft, and the application of the most stringent sonic boom criteria. They also urged the FAA to keep such operations out of metroplexes (at least 70 miles away) if the aircraft cannot meet the stringent standards.