The Federal Aviation Administration has pushed forward with weakening noise limits for commercial airplane takeoff and landing, a rollback that would allow supersonic aircraft (SSTs) to make a comeback. Developed in the early 1970s and last flown in the U.S. in 2003, SSTs are super-polluting passenger planes that burn 5 to 7 times more fuel than current commercial jets. In a 2019 study, the International Council on Clean Transportation found that supersonic air travel would exceed the subsonic limits for nitrogen oxides by 40%. The FAA’s fact sheet on supersonic planes notes that they were “retired nearly two decades ago because of the high cost of meeting the environmental restrictions on sonic booms, inefficient fuel consumption, and other factors.” Status: Proposed rule released April 13, 2020. Public comment period closes July 31, 2020.