Do You Know Why Airplane Windows Are Always Oval? The Answer Is Awesome

August 31, 2019 Updated: August 31, 2019

If you’re a frequent flyer, then you might have wondered why plane windows are always oval and never square. It may seem like a minor concern, but it’s actually a pretty big deal.

In fact, it could mean the difference between life and death.

Illustration – Shutterstock | Maridav

Square windows ruled the roost in early plane designs. But by the time the 1950s rolled around and the commercial jetliner became the newest and most fashionable mode of transportation, plane design features were forced to up the ante. Jetliners had the capacity to fly at greater speeds and high altitudes, says Science Alert, and many plane features were upgraded to accommodate these epic journeys.

But not, sadly, the windows.

A de Havilland 112 Venom single-seat fighter jet (foreground) and a de Havilland Comet four-jet air liner (background) grounded in 1949 (©Getty Images | Topical Press Agency)

It was a de Havilland Comet commercial jet plane that took the hit; one of their planes disintegrated in midair in 1954, and the culprit was quickly pegged as being the plane’s square windows. But why?

An accident investigation team found that a square window had been the source of a compromised structural integrity that killed every single passenger on board. It was a tragic loss, and engineers were duty-bound to get to the bottom of it.

Captain John “Cat’s Eyes” Cunningham in the cockpit of the new de Havilland Comet IV jet airliner with his co-pilot Pat Fillingham in 1958 (©Getty Images | Central Press/Hulton Archive)

An excellent informational video from Real Engineering explains exactly why square windows are so dangerous in planes that fly at high altitude, and, in turn, helps us to understand the demise of the de Havilland Comet. Commercial planes fly at approximately 30,000 feet for a reason; air density is lower than at lesser altitudes, so the plane itself and its passengers experience less turbulence.

Air pressure inside the cabin, therefore, needs to be maintained at a higher level so that the passengers can breathe. But wait; let’s do the math. If the pressure outside the plane drops but the pressure inside increases, then this creates a pressure differential.

Still with us? Great. Now let’s think about the square plane windows of the 1950s.

Square windows have four corners; these are weak points, liable to crack under pressure (literally, not figuratively, although never underestimate the inherent stress of air travel!). This is what happened to the de Havilland Comet; the square windows cracked and disaster ensued.

Curved windows are the logical alternative. They have no corners so they distribute the stress of pressure differentials evenly.

Illustration – Unsplash | Jaku Arias

The chief executive of the UK Flight Safety Committee, Dai Whittingham, spoke to the Daily Mail to shed further light on the matter. “Designers prefer oval windows,” Whittingham began, “because they can get a larger viewing area which suits the biggest range of passenger sitting heights.”

Oh, so oval windows are for passenger and flight crew convenience, too? Talk about a double upgrade! “The narrowest part of the oval will be designed to ensure the curve does not generate unsafe stresses in the surrounding material,” Whittingham clarified, explaining why oval windows are so much significantly safer than their square counterparts.

Illustration – Unsplash | Michael Fousert

“Recently we have started to see some designers opting for more rectangular shapes,” the flight safety expert admitted, “but these will always have curved corners.” We can rest assured that aesthetic preferences will never win over safety.

Unfortunately, it’s our moral duty to remember that it took two aircraft crashes and a remarkable feat of engineering for aeronautical experts to realize the inherent flaws in square windows. But since this remarkable revelation, all future aircraft have been designed with rounded windows to “protect the integrity of the fuselage,” says the BBC.

Illustration – Unsplash | Luke Porter

They’ve remained oval ever since the 1950s, and it works.

Fun fact: the very same principle applies to submarine and spacecraft doors and windows. So take a curious glance the next time you float, fly, or rocket your way out of Earth’s orbit (if you should be so lucky).

Those windows are oval for a reason.