Electronic Field Productions

August 7, 1955. Seattle, Washington. A crowd of around 250,000 people had gathered along Lake Washington for the annual Gold Cup hydroplane races. On boats in the lake, executives from nearly every major airline in the world watched from their seats. They were in Seattle for the annual International Air Transport Association meeting.

Boeing President Bill Allen was on one of those boats. He had personally invited them. Boeing was about to bet the entire company on its first commercial jet airliner, the prototype that would later become known as the Boeing 707. At that time, the aircraft was officially called the Boeing 367-80, but everyone at Boeing simply called it the Dash 80.

To convince the world, Allen had scheduled a simple flyover of the Dash 80 during the race. The pilot was Alvin "Tex" Johnston, Boeing's chief test pilot. He had been flying the Dash 80 for over a year. And he had a plan of his own.

As the four-engine jet roared over Lake Washington at nearly 490 miles per hour, Johnston rolled the entire 160,000-pound jet around its long axis in a perfect 1G barrel roll. For a few seconds, the aircraft was completely upside down over the heads of the crowd. Then he turned around and did it again.

It looked reckless, but it was not. In a properly flown barrel roll, the pilot coordinates the ailerons, which roll the wings, with the rudder, which keeps the nose tracking straight with no slip or skid, so the jet follows a smooth corkscrew path. Flown that way, everyone and everything inside still feels a steady 1G, the same force you feel sitting still on the ground. At no point were the wings or the airframe overloaded. That is exactly why Johnston always insisted the maneuver was completely safe.

In his autobiography, Tex later explained why he did it twice. "I knew that no one would believe what they had seen, so I turned around and I came back and repeated the same thing on a westerly heading."

The next morning, Allen called Johnston into his office. "What the hell were you doing?" he asked. "I was selling airplanes," Johnston replied. Allen's response, per the autobiography: "You know that. Now we know that. But just don't do it anymore."

And just like that, Johnston had sold the airplane. That October, Pan American Airways ordered 20 Boeing 707s. Other airlines quickly followed. The 707 went on to become America's first commercially successful jet airliner.

The Dash 80 prototype, the very same aircraft Tex rolled that afternoon, is now on permanent display at the Smithsonian's Steven F. Udvar-Hazy Center near Washington Dulles International Airport.

Sources: Tex Johnston's autobiography "Jet-Age Test Pilot," Smithsonian