Most People Will Go Their Entire Lives Without Ever Knowing Why Airplane Windows Are Round

Square or rectangular windows have corners, and corners are excellent at concentrating stress. Over time, under repeated pressurization cycles, those stress points can become microscopic cracks.

And microscopic cracks have a terrifying habit of growing.

When Aviation Learned the Lesson the Hard Way
In the early 1950s, commercial jet travel was still in its infancy. One of the most advanced aircraft of the era was the de Havilland Comet, the world’s first commercial jet airliner.

The Comet was revolutionary. It was faster, smoother, and more modern than anything that had come before it. Airlines and passengers were thrilled.

But the Comet had a fatal flaw.

Its windows were square.

At the time, engineers did not fully understand the long-term effects of repeated pressurization on metal structures. The Comet passed all ground tests. It flew successfully for months.