Why do planes have oval windows?

When traveling by plane, most of us prefer the window seat to enjoy the view from above. We have all noticed that airplane windows are oval, but have we ever wondered why they have this shape and are not, for example, square?

But they did not always have the same shape. If you are of a certain age and have traveled extensively by plane in your life, you certainly remember the time when airplane windows were square. The reason that airplane windows have changed shape is quite important and not just for aesthetic reasons.


As technology evolves, aerospace engineering has made huge leaps in aircraft technology, which means that more modern airplanes can carry more passengers and go faster. In the mid-20th century, airlines began flying at higher altitudes to save money as air density was lower up there, creating less resistance for airplanes. But higher altitudes came with problems. The pressure difference between the passenger compartment and the outside atmosphere causes a slight expansion in the fuselage, but not so small that it goes unnoticed.

For this reason, airplanes have been reshaped to increase safety, including windows. Square windows became a problem as their angles helped to expand the fuselage. Due to this pressure and the "vulnerable" corners, the windows were more likely to crack. In contrast, in round windows the pressure is distributed around the perimeter of the window and the risk of breakage is reduced.