'Gold-plated' design: Redundancy and extremely high safety factors allow aircraft to withstand forces far exceeding those encountered during routine flights

Unlike the Concorde, the Boeing 727 was not designed to travel at the speed of sound or faster. But in the air over Saginaw, Mich., in April 1979, that is exactly what one did. A Boeing 727, spiraling in an uncontrollable dive from 39 000 feet, reached a calculated Mach number of 0.96 - enough to put parts of the craft into transsonic territory, based on the varying airspeeds around the fuselage.