NASA’s X-59 Hits Mach 1.4 in Key Step Toward Quiet Supersonic Flight

More than seven months after its first flight, NASA’s X-59 jet hit the exact speed and altitude it needs to start flying quietly over U.S. towns — a critical step toward ending a half-century ban on supersonic flight over land.

NASA’s X-59 experimental aircraft reached Mach 1.4 at 55,000 feet on Friday, hitting the exact speed and altitude needed to begin testing public reaction to quiet supersonic flight over U.S. communities.

The flight, the aircraft’s 19th, lasted just over an hour and marked a key milestone in NASA’s Quesst mission, which is working to prove that a supersonic jet can fly over land without producing the disruptive sonic booms that have kept commercial supersonic flight banned over the United States for more than 50 years. NASA officials say the data the X-59 collects will ultimately go to the Federal Aviation Administration and international regulators to support lifting that ban.

The aircraft’s cockpit display showed 55,030 feet at the moment it hit mission conditions, according to NASA. Test pilot Jim “Clue” Less flew the aircraft. Mach 1.4 is roughly 924 mph.

Friday’s flight came one week after the X-59 broke the sound barrier for the first time, reaching Mach 1.1 at 43,400 feet during an 81-minute flight on June 5, according to NASA. Two days before Friday’s success, on June 10, NASA attempted to reach Mach 1.4 but stood down after the aircraft reached only Mach 1.2 at 49,000 feet.

Cathy Bahm, NASA’s low-boom flight demonstrator project manager, said the team ran short of fuel during the June 10 attempt because flying fast and high forces the X-59 to spend extended time in afterburner.

“For these high and fast flights, the aircraft spends a lot of time in afterburner, which consumes a lot of fuel quickly. So [on the June 10 flight] we only had enough fuel to achieve the one test point on the first flight, which was 1.2 Mach at 49,000 feet,” Bahm said.

Bahm said the team paused operations after that day’s first attempt to perform maintenance on the aircraft before trying again.

Reaching Mach 1.4 at 55,000 feet is not just a performance benchmark — it is the precise combination of speed and altitude NASA intends to use once the X-59 begins flying over selected American communities. Those flights, the ultimate goal of the Quesst program, are designed to let NASA survey residents on how they perceive the aircraft’s sound and feed that data to regulators.

Months of additional testing remain before that happens, NASA said. The agency still must evaluate the X-59 across a range of altitudes and conditions — up to a target ceiling of 60,000 feet and Mach 1.6 — to complete what it calls envelope expansion. After that, the program moves into an acoustic validation phase, during which crews will measure the aircraft’s supersonic acoustic signature — the “quiet thump” it is designed to produce — to confirm it performs as intended, NASA said in a June 12 blog post announcing the milestone.

During early supersonic flights, a NASA F-15 research aircraft flew alongside the X-59. Because the F-15 produces its own sonic boom, it masks any noise from the X-59 itself, while a shock-sensing probe mounted on the F-15 gathers early measurements of the X-59’s shock wave signature, NASA said. During the acoustic validation phase, ground- and air-based recording equipment, including an Automatic Dependent Surveillance-Broadcast receiver and data acquisition processor, will capture audio, waveform and spectral data, Aviation Week reported.

NASA aims to complete both the envelope expansion and acoustic validation phases by the end of 2026, the agency has said. Only then will it begin community overflights, which NASA has said will involve four to six locations, with roughly two test campaigns a year lasting about 30 days each and generating an estimated 80 to 90 individual noise exposure events. Sonic thumps during those tests are expected to range from about 70 to 87 PLdB — a measure of perceived loudness — with the nominal cruise level at 75 PLdB, allowing researchers to study how people respond to varying sound levels. NASA has said it intends to deliver the program’s findings to the International Civil Aviation Organization’s Committee on Aviation Environmental Protection by 2029.

The X-59 is built by Lockheed Martin’s Skunk Works division in Palmdale, California, under contract to NASA, as part of the agency’s Advanced Air Vehicles Program and its Commercial Supersonic Technology Project. The aircraft is 99.7 feet (30.4 meters) long with a 29.5-foot (9-meter) wingspan, an unusually slender shape that NASA says prevents the supersonic shock waves that normally combine into a sharp boom from merging, instead spreading them into a quieter thump. It is powered by a single General Electric F414-GE-100 engine producing 22,000 pounds of thrust, mounted atop the fuselage rather than underneath to reduce noise reaching the ground. Its maximum gross takeoff weight is approximately 24,300 pounds, and its empty weight is approximately 15,000 pounds.

Because the X-59’s long nose blocks a conventional forward view, the aircraft has no windshield. Instead, pilots rely on an eXternal Vision System, a set of cameras feeding a 4K display in the cockpit.

NASA is targeting a ground noise level of about 75 PLdB for the X-59’s sonic thump — roughly equivalent to a car door closing — compared with the 105 PLdB produced by the Concorde’s sonic boom, according to NASA.

The Federal Aviation Administration has barred civil aircraft from flying faster than the speed of sound over the continental United States since 1973, under a regulation known as 14 CFR Section 91.817. The rule was adopted because data available at the time showed sonic booms were unacceptable to communities on the ground. That conclusion followed a 1964 FAA test in which military jets flew supersonic over Oklahoma City eight times daily for six months; even though about three-quarters of surveyed residents said they could tolerate the booms, the test generated tens of thousands of complaints.

President Donald Trump signed an executive order on June 6, 2025, directing the FAA to repeal that regulation within 180 days and to issue a proposed noise-based certification standard for supersonic aircraft within 18 months. “By updating obsolete standards and embracing the technologies of today and tomorrow, we will empower our engineers, entrepreneurs, and visionaries to deliver the next generation of air travel, which will be faster, quieter, safer, and more efficient than ever before,” the order states. The FAA is now conducting related rulemaking, designated RIN 2120-AM15, in response to that order.

The U.S. House of Representatives passed companion legislation, the Supersonic Aviation Modernization Act (H.R. 3410), by voice vote on March 24, 2026. The bill would require the FAA to revise its overland supersonic rules within a year of enactment, provided no sonic boom reaches the ground, and to issue a final noise rule by April 1, 2027. The legislation awaits action in the Senate.

Industry analysts do not expect overland supersonic passenger flights to begin immediately even after the regulatory changes take effect, since no commercially certified civil supersonic aircraft currently exists. Boom Supersonic, a U.S. company developing the Overture airliner, has said it is targeting passenger service around 2029, with United Airlines and Japan Airlines among carriers that have placed orders; the Overture is designed to fly supersonic primarily over water. The company’s smaller XB-1 demonstrator, nicknamed “Baby Boom,” first flew in March 2024 and was retired in early 2025 after 13 flights, two of which reached Mach 1.1. Spike Aerospace is among other companies pursuing supersonic aircraft designs, and Trump’s executive order directs the FAA to pursue international regulatory alignment and bilateral agreements, since supersonic routes require access to other countries’ airspace. Analysts have projected the early 2030s as a more realistic window for the start of commercial supersonic service over the continental United States.

NASA rolled out the X-59 on Jan. 12, 2024, at Lockheed Martin’s Skunk Works facility in Palmdale. The aircraft completed taxi tests in July 2025 and made its first flight on Oct. 28, 2025, taking off from Air Force Plant 42 in Palmdale and landing at NASA’s Armstrong Flight Research Center at Edwards Air Force Base. That flight lasted 67 minutes and reached only about 230 mph and 12,000 feet, well below the speed of sound. A second test flight on March 20, 2026, was cut short by a technical glitch. By early June, the aircraft had completed roughly 16 flights in the preceding 90 days, including its first flight with the landing gear retracted, establishing a steady test rhythm before its first supersonic flight, according to NASA.

The Quesst mission was formally established in 2021, building on conceptual design work that began in 2016, and NASA awarded the aircraft’s development contract to Lockheed Martin under its Low-Boom Flight Demonstrator program. To hold down cost and schedule risk, the X-59 borrows components from existing aircraft, including F-16 Block 25 landing gear, a T-38 canopy and a GE F414 engine adapted from the F/A-18. The project was delayed several times — it was initially expected to fly in 2022 — before its first flight last October.