While believing that the FAA’s recent proposal on special flight authorizations for civil supersonic flight is a key step toward making such operations a reality, manufacturers are seeking several changes to stipulations that they fear serve as a barrier to testing over land.
In June, the FAA released a notice of proposed rulemaking (NPRM) to facilitate special authorizations for supersonic flights primarily for flight-testing purposes. Deadline for comments to the NPRM (FAA-2019-0451) was August 27. Coming at the behest of a congressional directive, the proposal is being praised in the industry as “an important first step toward enabling the next generation of environmentally responsible supersonic aircraft.”
The ability to test developments in new supersonic designs has been hamstrung by the current regulations prohibiting supersonic flight over land, even in testing. Special flight authorizations would facilitate such testing and enable manufacturers to build important operational and noise data, they say. “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,” the Aerospace Industries Association and General Aviation Manufacturers Association said in joint comments on the proposal. “We therefore welcome the FAA’s attempts to streamline the authorization process for such flights.”
The associations, which represent the range of business, general aviation, commercial and aerospace manufacturers, acknowledged 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,” they said.
To that end, the associations expressed the belief 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 around airports.
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 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.”
While accepting that any steps forward must come with environmental responsibility, the manufacturing representatives had a number of concerns about restrictive language in the NPRM. Most of those commenters, also including 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 any 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 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” 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.”
Other comments encouraged the FAA to better define what testing might receive flight authorization. Boom questioned the stipulation that applicants for special flight operation demonstrate that the tests could not be performed over the ocean. The company said such a stipulation is “not economically reasonable and undermines safety.”
Aerion and GE Aviation, meanwhile, encouraged the facilitation of the transfer of overwater flight results and parameters to over-land flight trials outside defined testing areas. “Otherwise, the over-ocean supersonic flight testing will have to be duplicated in subsequent flight testing inside the NAS under an FAA special flight authorization, which would entail needless expense, generate only redundant information, and lead to unnecessary duplicative flights and the associated impacts thereof,” Aerion said.
Further, the AS2 partners questioned stipulation that applicants planning to operate outside a defined test area show that the conditions and limitations of the flight “represent all foreseeable operating conditions and are effective on all flights.” This requirement is “unreasonable and unachievable,” Aerion contended and suggested that be replaced with standards based on available sonic boom prediction and control technology.
Aerion engine partner GE Aviation agreed. “The requirement for previous tests to represent all foreseeable operating conditions is far too restrictive,” the engine-maker said in its comments. “This requirement should be changed to reflect technological capabilities which allow reliable prediction of sonic boom formation and the ability to adapt to manage and mitigate any sonic boom impacts.” But any process for approving flights outside test areas should protect against sonic boom impacts, GE Aviation added.
Boom further encouraged the expansion of test ranges. “The industry will need new supersonic test areas if even a handful of manufacturers seek to engage in development, certification, and production of supersonic aircraft. Existing supersonic airspaces are too small, too crowded, and too few to support the ambitions of the industry.”
Despite the different concerns, the manufacturers were encouraged by the NPRM.
“We appreciate the greater clarity the FAA has sought to add to the existing application process and believe this will improve outcomes for manufacturers, as well as communities and the environment, by setting clearer expectations of what is required,” the engine maker said, adding it was “pleased with the direction the FAA is moving in with this proposed rule.”
“We believe it is possible to expeditiously integrate supersonic testing into the National Airspace System while preserving existing standards of protection,” Boom said, adding it “applauds” the FAA’s leadership do date on the issue. “We appreciate the vital, data-driven work that the FAA does to maintain an appropriate level of environmental protection, while balancing numerous considerations imposed by law.”