The Surprising 1950s Disaster That Made Airplane Windows Round: An Essential Safety Story

Published on 28 October 2025 11:55 AM IST

The Surprising 1950s Disaster That Made Airplane Windows Round: An Essential Safety Story

Have you ever settled into your seat on a flight and looked out through the small, oval window and wondered: Why are these not square? After all, windows in almost every other building, bus, or train are rectangular.

The answer is one of the most crucial lessons in aviation history, born from a series of tragic disasters in the 1950s that forever changed how aircraft are built. This simple, curved design is not just for aesthetics—it’s a critical safety measure that saves lives on every flight.

The Fatal Flaw: Stress Concentration

To understand why a round window is necessary, you first have to understand cabin pressurization.

When an aircraft climbs to high altitudes (around 30,000 feet), the air outside is too thin to breathe. To keep passengers safe, the cabin is essentially pumped full of air, making the pressure inside much greater than the pressure outside. This process causes the airplane’s cylindrical fuselage to swell, like a giant soda can being pumped with air.

This swelling puts immense stress on the aircraft’s skin, especially around any cutouts—like windows. In an engineering context, any sharp corner, such as the 90-degree angle of a square window, acts as a stress concentration point.

Imagine taking a piece of paper and cutting a small, sharp V-notch in the edge. When you try to tear the paper, the force concentrates right at that notch, and the paper rips easily.

In the early jet age, the sharp corners of square windows did the exact same thing to the metal fuselage. The stress was focused on those four small areas, and with the repeated pressurization and depressurization cycle of thousands of flights, the metal began to crack due to a phenomenon called metal fatigue.

The De Havilland Comet Catastrophe

This engineering lesson was learned the hardest way possible with the De Havilland Comet, the world’s first commercial jetliner, introduced in 1952.

The Comet was a marvel, flying higher and faster than any plane before it, and it was initially fitted with standard square windows. But between 1953 and 1954, three Comets tragically broke apart mid-air at high altitudes.

A massive investigation revealed the shocking truth: the failures were not caused by a bomb or engine trouble, but by structural failure originating at the corners of the square window cutouts. The repeated stress cycles caused tiny, invisible cracks to grow until the fuselage ripped open catastrophically.

The Life-Saving Fix: A Smooth Flow of Pressure

The solution was to eliminate the corners entirely.

By making the windows round or oval, the load is evenly distributed. The pressure and stress from the pressurized cabin flow smoothly around the curvature of the window opening, rather than concentrating in a specific point.

This ensures that the airplane can safely withstand the tens of thousands of pressurization cycles it will undergo during its operational lifetime. Every time you see that smooth, curved airplane window, you are looking at a permanent, life-saving safety feature directly resulting from a painful, essential lesson in aviation history.