Reason Airplane Windows Are Round

Stress builds up most at the sharp corners of a square window and therefore, eventual cracking of windows. British-built Comet aircrafts went through this problem in the early days of this discovery. This problem was consequently rectified by installing rounded windows.

This Is the Important Reason All Airplane Windows Are Round
Joanie Faletto

The round windows on airplanes aren't a frivolous design choice. It's a life-saving engineering innovation. If commercial plane windows were square like the ones in your house, the whole plane would disintegrate mid-flight, and no one wants to deal with any of that on their way to Cancún.

Don't Be a Square
Around the mid-twentieth century, commercial airlines started flying their planes at higher altitudes. This plan was ultimately a money-saving move, as lower air density means less drag on the plane, and less drag means less fuel is wasted. Flying in the upper atmosphere means a smoother ride, too.

To make planes suitable for flying at higher altitudes, airlines had to make some design changes. First, the plane cabin had to be pressurized so passengers could, well, breathe. Secondly, the plane had to be cylindrical in order to withstand the newly increased internal pressure. Voila! The perfect plane — or so you'd think. In the 1950s, three airplanes crashed when the fuselage was ripped to shreds because engineers overlooked one crucial design flaw: They used square windows.

Square windows are problematic for high-flying planes because of a slight difference in atmospheric and cabin pressure. This difference causes the cabin to expand very slightly, which puts stress on the material — in this case, the window frames. That stress builds most at the sharp corners of a square window, and when the stress becomes too great, crrrack! With an oval window, however, the stress flows more smoothly around the whole thing, avoiding a potentially destructive buildup of stress.

Get in Line

Since we're on the topic of airplane windows, you may have noticed another quirk about them: They're often not aligned with the rows of seating. Don't blame the airplane manufacturers; this issue is solely up to the airline that purchases the plane. It's their property, after all. The manufacturers build the planes with row positioning, legroom, and window placement in mind, and pass their recommendations along to the airline. They're rarely followed, however. Depending on the airline, different planes stack more rows together than others. Once the number of rows changes, the window alignment gets — sorry — thrown right out the window.