Noise NPRM Proposes New Supersonic Airplane Category

By Scott Spangler on April 6th, 2020

Aerion_AS2_BlueSky_LRAs most of us are coping with the geographic constraints of staying at home, one hopes the FAA did not schedule the release of the NRPM proposing Noise Certification of Supersonic Airplanes [FAA-2020-0316] for March 30, 2020 as an Easter egg or aviation irony. Bu then again, with much of the FAA working from home, which surely gives a greater sense of freedom than when confined in their office cubicles, one never knows.

What is certain, however, is that reading the 65-page NPRM was truly enjoyable because it offered a concise narrative arc on the reawakened interest in civilian supersonic flight. In proposing the noise certification standards, the NPRM proposes a new category of airplanes, Supersonic Level 1.

Add SSL1 to your dictionary of aviation abbreviations and acronyms. It has a maximum takeoff weight of 150,000 pounds and a maximum operating cruise speed of Mach 1.8. And the proposed noise certification requirements apply only to the subsonic landing and takeoff (LTO, another one for your dictionary) cycle standards. This proposal does not change in any way the §91.817, which prohibits the creation of sonic booms over the terrestrial United States.

Irony aside, the NPRM’s timing is important because several companies, such as Aerion Supersonic and Boom Supersonic, are developing supersonic aircraft. And their quest for type certificates cannot proceed without first meeting the supersonic noise requirements, which do not now exist.

Many right now are recalling finger-plugged ears as they watched the Concorde take off for its fly-bys at EAA Oshkosh and asking “Huh?” The NPRM explains that Part 36 still includes noise standards for the Concorde, and the Concorde alone. Even though the Concorde retired from the sky decades ago, its type certificate remains valid.

f-22_2The proposed noise certification regulations are not in any way related to the Concorde standards the FAA issued in 1978. Aviation technology has come a long way since then. Like the military fighters of the era, supersonic flight depended on the fuel-guzzling roar of afterburners. The F-22 introduced the ability to cross the supersonic threshold to supercruise without using afterburner, and that was in the late 1990s. The advancement of airframe and powerplant technology has continued it forward march.

So, what are the proposed SSL1 noise certification standards? The limits are quieter than Stage 4 LTO requirements met by most subsonic jets flying today, but they are a bit louder than the current certification level of Stage 5 for the same aircraft weights. This is an allowance for “the unique technologies and design requirements for supersonic aircraft to maintain long-distance supersonic flight.”

When this all will come to pass is unknown. A safe assumption would be that the NPRM is in the cue for its debut in the Federal Register, and that once published, the public will have 90 days to submit its comments. A speedy conclusion is one thing we can count on. Let’s hope we can once again leave the house before the FAA issues its regulatory decree. – Scott Spangler

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One Response to “Noise NPRM Proposes New Supersonic Airplane Category”

  1. Stephen Casciotta Says:

    Noise is working on F-4s and F-14s in afterburner. That’s loud, flying over the community breaking windows etc.

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