The leading US developers of supersonic aircraft called on the Department of Transportation (DOT) Aug. 27 to modify its proposed rule on supersonic flight authorizations, arguing the proposal’s wording amounts to an effective prohibition on all supersonic flight.

The comments came in response to DOT’s June 28 notice of proposed rulemaking (NPRM) to streamline the application process for supersonic flight authorizations.

The rulemaking—which is expected to be published in the Federal Register by year-end—will not constitute a repeal of the current prohibition on overland flights in excess of Mach 1, although FAA will reserve the authority to approve supersonic operations on an individual basis.  

In comments submitted to DOT Aug. 27, Nevada-based Aerion wrote that the rulemaking’s requirement that test flights cause “no measurable sonic boom overpressure to reach the surface … would effectively create a ban on all supersonic flight.”

“This requirement does not recognize the possibility for a sonic boom or evanescent wave to be produced that is barely noticeable on the ground—if at all—but can still be detected by some scientific measurement method,” the company wrote.

Aerion suggested DOT eliminate the “no measurable overpressure” standard, instead allowing companies to perform environmental analyses using predictive technologies that can accurately model the noise impacts of supersonic booms. The FAA, in turn, should evaluate those impacts according to the same regulatory standards as used for other modes of transportation, such as subsonic aviation and commercial space operations, the company suggested.

In separate comments submitted Aug. 27, airliner developer Boom Supersonic wrote that the NPRM’s requirement that manufacturers first demonstrate that test flights could not be performed over the ocean in order to justify later overland flights “is not economically reasonable and undermines safety.”

Boom wrote: “For a new entrant manufacturer located far from a coast, testing supersonic aircraft over the ocean requires setting up additional test facilities that will cost many millions of dollars. For such an enormous expense, the public may be spared a few dozen half-second disturbances (on par with cracks of thunder, motorcycles backfiring, and other noises already tolerated in the environment) per year.”

Ben Goldstein,