FAA clarifies supersonic flight rules as Boom XB-1 jet hopes to break Mach 1.3 this year

Zac Hall | Jan 6 2021 - 10:17 am PT

Supersonic flight is set to make a comeback and go further than ever before in this decade. Today the Federal Aviation Administration published new guidance to support this effort by clarifying existing policy and potentially streamlining the regulatory side of supersonic testing.

The Department of Transportation currently does not authorize supersonic flight by default. This means developing and testing technology like Boom’s XB-1 supersonic jet will require special authorization from the DOT and FAA to fly over Mach 1 speeds.

The FAA published a new document it calls the final rule “to facilitate the safe development of civil supersonic aircraft.” While the document does not contain new policy, it does provide a modern interpretation on regulation that dates back to the 1970s. The final rule is based on FAA conclusions reached while considering feedback from aviation companies and local governments alike.

National Environmental Policy Act

In the final rule, the FAA includes arguments made by Boom on ways to speed up supersonic testing applications while complying with the National Environmental Policy Act:

Boom initially presents two factual conclusions. Boom’s first conclusion is that FAA would be unlikely to identify any significant sonic boom noise impacts for individual supersonic flight test programs under the FAA’s threshold of significance for noise impacts in its NEPA procedures (FAA Order 1050.1). Boom’s second conclusion is that the FAA programmatically could examine all supersonic test flight campaigns covering all applicants in a single year without the impacts triggering the FAA’s threshold of significance for noise.
Boom supports these conclusions with metrics from previous flights of the SpaceX Falcon Heavy landings and operations of the Concorde. Based on its conclusion that impacts of special flight authorizations would never reach FAA’s threshold of significance for noise impacts, either individually or cumulatively on an annual basis, Boom proposes a series of qualifying criteria that, if met, should lead FAA to presume no significant impacts exist.

The FAA did not bite, nor did it accept an argument that pre-approved circumstances could be determined that would expedite supersonic testing approval.

Supersonic flight testing

The final rule does provide companies testing supersonic flight with some clarifications that simplify which steps of testing must receive approval and where tests can be conducted. Here’s a breakdown of some of the highlights:

Takeoff and landing testing does not require special approval since neither occurs at supersonic speeds that create environmental noise concerns
Companies are allowed to share locations for supersonic testing versus establishing separate test sites, although each party will require FAA approval before testing
Approved supersonic testing locations are not required to be military operation areas that could limit civil supersonic test opportunities
Companies are encouraged to use software models for predicting sonic boom ground impacts

The FAA also clears the way for approving supersonic tests focused on gathering noise data. The idea here is that you can’t measure real noise levels from supersonic flight without actually conducting a test flight first. Because there are no standards for assessing noise level during supersonic flight, this is an area that will likely gain more direction in the future.

Over ocean required

Existing supersonic flight authorization requires tests to be conducted over oceans and not land in part to isolate the sound of a sonic boom from reaching land. The document cites arguments from Boom that seek to remove this requirement in future authorizations, but the FAA decidedly objected to Boom’s argument:

Boom raised economic concerns with the overocean provision. Boom stated that FAA’s 1970s-era economic rationale for the prohibition on supersonic overland flight and application process for overland testing is not valid because it was based on a market assessment of supersonic aircraft that did not materialize.
Boom also stated that the overocean requirement is not economically reasonable because testing supersonic aircraft over the ocean would require manufacturers located farther from the U.S. coastline to incur enormous expenses to set up additional test facilities with closer proximity to the ocean. Boom added that “for such an enormous expense, the public may be spared a few dozen half-second disturbances per year.” […]
Rather, Boom’s comment suggests that the requirement could pose a financial obstacle to Boom’s particular business plans, not that the regulation in general is economically unreasonable.

Each supersonic test application will still require the applicant to provide a reason why over ocean testing isn’t possible for each specific test before approval is considered. For now, supersonic testing on land will be limited to specific instances like measuring sound which couldn’t be conducted over oceans.

Heavily cited in the final rule document, Boom Supersonic unveiled the design of its XB-1 test plane in October and plans to conduct multiple test flights with the hardware this year. Read the full document here.

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