NASA’s experimental X-59 aircraft has reached an important milestone in the Quesst program, flying for the first time at the speed and altitude planned for future community overflights that will test public reaction to its quiet supersonic sound.

During a test flight on Friday, June 12, 2026, the aircraft reached Mach 1.4, or about 1,487 kilometers per hour, at an altitude of 55,000 feet. These are the conditions in which the X-59 is expected to fly later in the program, when NASA begins collecting data on how people on the ground perceive its significantly quieter sonic signature.

The milestone came only days after the X-59’s first supersonic flight, during which the aircraft flew at Mach 1.1. While that flight confirmed that the aircraft performed as expected as it entered the supersonic regime, reaching Mach 1.4 at 55,000 feet represents a more significant step because it matches the planned mission conditions for future testing.

The X-59 was developed to fly at supersonic speeds without producing the loud sonic boom associated with conventional supersonic aircraft. Instead, it is designed to create a much softer “sonic thump”. Such technology could play an important role in the future of civil supersonic flight over land, which has long been restricted because of the noise produced by traditional supersonic aircraft.

NASA said the aircraft still faces months of performance testing. The current flights are part of the gradual expansion of the aircraft’s flight envelope, during which the team evaluates how the aircraft performs at different speeds and altitudes, while test pilots carry out a series of maneuvers.

During these early supersonic flights, the X-59 is accompanied by a NASA F-15 research aircraft. Since the F-15 is a conventional supersonic jet that also produces sonic booms, its presence currently makes it difficult to isolate the sound generated by the X-59 itself. In upcoming flights, the F-15 will carry a shock-sensing probe to collect early measurements of the X-59’s shock wave signature and supersonic performance.

After further tests at different altitudes and in various conditions are completed, the program will move into the acoustic validation phase. During this stage, researchers will make detailed measurements of the aircraft’s actual supersonic acoustic signature and confirm whether the X-59 is producing the quiet “sonic thump” it was designed to create.

The ultimate goal of the Quesst program is to fly the X-59 over several U.S. communities and gather feedback from residents about the noise produced by supersonic overflights. The data could help regulators consider future rules for commercial supersonic flights over land.