Crossfield's body was found in the wreckage Thursday in the mountains about 50 miles northwest of Atlanta, a day after the single-engine plane he was piloting dropped off radar screens on a flight from Alabama to Virginia. There were thunderstorms in the area at the time.

The cause of the crash was under investigation. Crossfield was believed to be the only person aboard.

During the 1950s, Crossfield embodied what came to be called "the right stuff," dueling the better-known Chuck Yeager for supremacy among America's Cold War test pilots. Yeager broke the sound barrier in 1947; only weeks after Crossfield reached Mach 2, or twice the speed of sound, Yeager outdid him.

The Cessna 210A in which Crossfield died was a puny flying machine compared with the rocket-powered aircraft he flew as a test pilot. During his heyday, he routinely climbed into some of the most powerful, most dangerous and most complex pieces of machinery of his time, took them to their performance limits or beyond - or "pushed the envelope," as test pilots put it - and usually brought them back to Earth in one piece.

"He's really one of the major figures," said Peter Jakab, aerospace chairman at the Smithsonian Air and Space Museum. "He was not only the great cutting-edge research pilot ... but after that, he continued to be a great adviser and participant in all aspects of aerospace."

Crossfield, who lived in Herndon, Va., and flew regularly into his 80s, was a member of a group of civilian pilots assembled by the National Advisory Committee for Aeronautics, the forerunner of NASA, in the early 1950s. Yeager did his test-flying as an Air Force pilot.

Crossfield flew Mach 2 on Nov. 20, 1953, when he hit 1,300 mph in NACA's Douglas D-558-II Skyrocket. The plane reached an altitude of 72,000 feet.

After leaving NACA, he had a major role in the development of the X-15 rocket plane and piloted it on several of its early test flights in the early 1960s.

NASA Administrator Michael Griffin hailed him as "a true pioneer whose daring X-15 flights helped pave the way for the space shuttle."

"We keep talking about test pilots, but there is no such thing as a `test pilot,"' Crossfield said in a 1988 interview with Aviation Week & Space Technology. "They are all just people who incidentally do flight tests. ... We should divest ourselves of this idea of special people (being) heroes, if you please, because really they do not exist."

In "The Right Stuff," Tom Wolfe's history of the dawn of the space age, Wolfe portrayed Crossfield, Yeager and other members of the brotherhood of test pilots as possessors of "the right stuff," which the author defined as "the ability to go up in a hurtling piece of machinery and put his hide on the line and then have the moxie, the reflexes, the experience, the coolness, to pull it back in the last yawning moment - and then to go up again the next day, and the next day, and every next day."

Born in Berkeley, Calif., in 1921, Crossfield interrupted his studies at the University of Washington to join the Navy in 1942. He learned to fly a variety of aircraft during his Navy service.

Attempts to break the sound barrier in the years following World War II involved high stakes and some big egos.

On Oct. 14, 1947, Yeager finally reached the landmark, pushing his orange, bullet-shaped Bell X-1 rocket plane, past 660 mph over the Mojave Desert in California. His feat was kept top secret for about a year.

The now 83-year-old Yeager, in his book "Yeager: An Autobiography," described friction between the military pilots and the civilian NACA pilots. He groused that Crossfield "was a proficient pilot, but also among the most arrogant I've met. ... None of us blue suiters was thrilled to see a NACA guy bust Mach 2."

The competition did not end at Mach 2. On Dec. 12, 1953, just a few days before the 50th anniversary of the Wright brothers' first flight, Yeager bested Crossfield when he flew an X-1A to a record speed of more than Mach 2.4, or more than 1,600 mph.

The upcoming Wright anniversary had weighed on his mind, Yeager wrote: "The television networks had scheduled special programs about Crossfield and his Mach 2 flight. ... Our plan was to smash Scotty's record on December 12."

Nowadays, the best fighter jets can fly well over Mach 2.

Crossfield left NACA in 1955 to work for North American Aviation on the X-15 project, including its first flight, an unpowered glide, in 1959. Other early X-15 test flights were made by pilots Joe Walker and Robert White.

In one of his test flights, Crossfield reached about three times the speed of sound on Nov. 15, 1960, in an X-15 launched from a B-52 bomber. The plane reached an altitude of 81,000 feet.

There were some close calls. During an X-15 flight in 1959, one of the engines exploded. The emergency landing broke the aircraft's back just behind the cockpit, but Crossfield was not injured, according to the Edwards Air Force Base Web site.

Less than a year later, a malfunctioning valve caused a catastrophic explosion during a ground test while Crossfield was in the cockpit. He again escaped injury.

In later years, he was an executive for Eastern Airlines and Hawker Siddley Aviation and a technical consultant to the House Committee on Science and Technology.

"I am an aeronautical engineer, an aerodynamicist and a designer," he told Aviation Week & Space Technology. "My flying was only primarily because I felt that it was essential to designing and building better airplanes for pilots to fly."

More recently, Crossfield had a key role in preparations for the attempt to re-enact the Wright brothers' flight on the 100th anniversary of their feat on the sand dunes near Kitty Hawk, N.C. Crossfield trained four pilots, and one of them, Kevin Kochersberger, was selected for the Dec. 17, 2003, attempt.

But in the end, unsuitable weather doomed the attempt to get the replica into the air. The plane plopped into wet sand as the crowd of 35,000 groaned.

Among his many honors, Crossfield was inducted into the National Aviation Hall of Fame in 1983.