In the beginning of the 1950s, de Havilland developed Comet, the world’s first commercial jet airliner. It was literally a miracle. But a year later, it fell to pieces right in the sky. In several months, 2 more airplanes crashed.
Engineers conducted a diagnosis of each screw of the aircraft and found the problem: the windows were square. The thing is, pressure builds more around the corners of square windows and this pressure only increases during a flight. So it was decided to make windows round. Thanks to this decision, flights are way safer now.