FAA Proposed Supersonic Overland Rule Draws Technical Criticism Over Sonic-Boom Standard

The FAA published a proposed rule on July 2, 2026 that would reopen US airspace to civil overland supersonic flight by replacing the existing speed-based ban with a performance-based system tied to sonic-boom intensity. Under the proposal, supersonic operations would be permitted if boom effects at the surface remain below a maximum peak sonic-boom overpressure of 0.11 psf, covering both primary and secondary booms. Operators would demonstrate compliance through measurement, modeling, or another FAA-approved means.

Environmental groups including Earthjustice and the Sierra Club argue the FAA has not demonstrated that 0.11 psf represents an acceptable exposure level for communities, and that peak overpressure does not adequately capture human perception of sonic booms. NASA has investigated perception-based metrics such as PLSEL, while conventional noise certification uses metrics like EPNL, which account for frequency, duration, and tonality. The FAA identifies Mach Cutoff Operations as one possible compliance technique, in which a combination of altitude and Mach number under specific atmospheric conditions causes the boom to refract back into the atmosphere before reaching the ground at significant intensity. The Airline Pilots Association questions whether Mach Cutoff Operations can be maintained throughout an entire commercial flight, since the cutoff condition varies with altitude and atmospheric state, and notes that temperature gradients, winds, and atmospheric layering can alter boom propagation.

The FAA's proposal acknowledges the need for further research, including data expected from NASA's Quesst/X-59 program. Boom Supersonic's Overture, designed to cruise at Mach 1.7 carrying 64 to 80 passengers, has targeted a 2029 entry into service, and Spike Aerospace's S-512 is also identified as a program the rule could affect.

This proposal belongs to a category of rulemaking where the certification metric itself becomes the primary battleground, since the number chosen at the surface determines which aircraft designs and routes clear the bar. Sonic-boom regulation has historically hinged on a single threshold standing in for a more complex human response, and the dispute over peak overpressure versus perception-weighted measures like PLSEL or EPNL shows how a seemingly technical parameter carries the whole policy outcome.

For supersonic programs, the practical effect runs through route economics more than through go/no-go viability. Boom Supersonic has built its business case around near-Mach-1 overland segments and over-water supersonic cruise, so the rule is not required for Overture to fly, but a workable 0.11 psf standard could unlock overland segments such as New York to Los Angeles that are currently closed to sustained supersonic cruise. Spike Aerospace's S-512 sits in the same position, with commercial viability tied to how liberal the eventual overland standard turns out to be.

The open question is whether the FAA settles on peak overpressure alone or folds in a perception-based or duration-weighted metric before finalizing the rule, and how much weight NASA's Quesst/X-59 boom data carries in that decision. Operators and airframers building routes around Mach Cutoff Operations will also need clarity on whether that technique can be certified as reliably repeatable across varying atmospheric conditions, or whether it remains a supplementary tool alongside other compliance paths.