Complex sentence: The FAA and the ICAO are working on a sonic boom standard to allow supersonic flights overland; the NASA plans to fly a low-boom demonstrator in 2021 to assess public acceptability of a 75 boom, lower than Concorde's 105 PNLdB.
Split into simpler sentences: The FAA and the ICAO are working on a sonic boom standard to allow supersonic flights overland. The NASA plans to fly a low-boom demonstrator in 2021 to assess public acceptability of a 75 boom, lower than Concorde's 105 PNLdB.