At an event in Paris on Monday, Acting FAA Administrator Dan Elwell said the agency is working to "enable the return of civil supersonic travel, while ensuring the environmental impacts are understood and properly addressed."

Later this week, the FAA will issue a proposed rule for "special flight authorization for supersonic aircraft," Elwell said. This is the first step toward revising the FAA's 45-year-old rules governing supersonic transport.

U.S. startups Aerion, Boom Supersonic and Spike Aerospace are working to reintroduce supersonic passenger travel for the first time since the Anglo-French Concorde retired in 2003.

The rule "modifies and clarifies existing regulatory procedures for a more efficient way to obtain FAA approval to test supersonic aircraft."

The rule "will provide a streamlined, clear line of sight on how to gain approval to conduct flight testing. This is a necessary, key step for further research and development in an emerging segment – and ultimately bring their aircraft to market," Elwell added in remarks provided by the FAA.

According to a draft of the FAA proposal reviewed by Reuters, the agency said the proposed updates "are intended to support the growth of the civil supersonic industry" and will "provide increased clarity and information to applications as to the requirements for special flight authorizations to test supersonic aircraft."

In February, Boeing Co said it had made a significant investment in supersonic business jet developer Aerion, as the world’s biggest planemaker looks to tap into rising demand for high-end aircraft that can reduce travel time.

Boeing will provide engineering, manufacturing and flight testing services for Aerion’s $120 million supersonic business jet, which is slated for its first flight in 2023.

Congress last year approved legislation directing the FAA to issue proposed rules setting noise standards for landing and takeoff, and noise test requirements for civil supersonic aircraft by March 2020, and modernizing the application process by December 2019.

Next generation supersonic jets, while quieter and more fuel efficient than the Concorde, have difficulty meeting existing noise levels and carbon emissions standards for conventional planes due to engine constraints and higher fuel burn.

(Reporting by David Shepardson; Editing by Bill Berkrot)