How did a test pilot break the sound barrier, and why did Concorde retire?

A test pilot broke the sound barrier by flying a purpose-designed aircraft and showing that flight at the speed of sound was safe in the right aircraft. The "barrier" was a big rise in drag and other bad effects as an aircraft nears the speed of sound. The term came into use in World War II, when fighter pilots met compressibility effects that deterred further acceleration. At first it seemed to make faster speeds very difficult or impossible.

In 1947 Chuck Yeager demonstrated that safe flight at the speed of sound was achievable in purpose-designed aircraft. On 14 October 1947, over the Mojave Desert, he flew the Bell X-1, nicknamed Glamorous Glennis for his wife. The plane was designed with an adjustable horizontal stabilizer, because engineers had predicted big trim changes near the speed of sound.

Two nights before the flight, Yeager fell off a horse and broke two ribs. He could not use his right arm to pull the cockpit hatch shut. His friend Jack Ridley sawed off the end of a broom handle for him to use as a lever, and the flight went ahead.

The airliner that made supersonic flight routine for paying passengers was Concorde, which entered service on 21 January 1976. It more than halved travel times, but sonic booms limited it to routes over the ocean, its costs rose to more than six times the projections, and the 1973 oil crisis made airlines wary of thirsty planes. After the only fatal Concorde accident, in July 2000, service was suspended, and the last aircraft retired in 2003.