Why airplane windows are no longer square: everything changed in the 1950s (and fortunately so)

Maybe you are one of those people who feel the seven evils when they fly. Or maybe you are one of those people who look for the window to spend the whole flight contemplating with wonder what is there.

Whatever your type, you will have noticed the peculiar shape of these windows. They are unlike any other, neither car windows nor boat windows (to which we could actually devote an article of our own)… They are in fact a mixture of all of these and none of them.

Beyond transportation, we are used to seeing square and rectangular windows all around us. In the case of airplane windows (called portholes), they are always round, but not quite. But it wasn't always that way. Decades ago, when commercial aircraft production began, square windows were the norm. Why have they changed?

The practice of a once new and fascinating medium – flight, which is still an event today – was fundamental and, as you can imagine, tragic. After several tragic accidents, manufacturers realized that this first system was not the right one.

Fatal accidents

It was the 1950s, and as commercial airplanes got bigger and bigger, some began to “disintegrate” in mid-air. Literally: one of them, known as Comet 1, for example, disintegrated in midair in separate events in 1953 and, a year later, in 1954. The cause? Square windows.

After careful investigation (because at the time it was not easy to identify this error), engineers realized that the sharp edges of these openings created natural weak points in the spacecraft, causing “metal fatigue fractures”. In other words, once the plane was assembled, these corners were stressed by the pressure they were subjected to and easily weakened until they exploded.

It should also be noted that at that time, aircraft flew higher and faster than today, believe it or not. So fatal errors had to be modified.

The great solution

The higher the airplane, as we might expect now that we have the knowledge, the greater the pressure variations during flight, especially during climb or descent to altitude. These moments have become moments of opportunity.

Round shaped windows are better able to withstand these conditions, as they allow for a more even pressure distribution over the window surface, reducing the risk of cracking or breaking. They are also easier to install than square or rectangular windows, which has become essential for airlines that must regularly replace damaged or worn windows.

You may also notice several layers of acrylic (not glass, as with other windows) between the person and the exterior of the aircraft. These layers provide additional protection from rain, wind and fog. Typically, the center panel also has a small hole in it. This allows for pressure equalization between the cabin air and the air between the outer and center window.