Tourists take photos from the plane window. Photo: Alina Matveycheva/Pexels .
Nearly every commercial aircraft today uses the same type of window: rounded rectangular windows, sometimes closer to oval than square.
For passengers, these are simply round windows to watch the clouds and sky. But according to Reader's Digest , the curved lines at the four corners are the key details that help the plane's body not crack when flying at an altitude of tens of thousands of meters.
At cruising altitude, the cabin is pressurized so that occupants can breathe normally, while the outside air is thinner and has much lower pressure. The fuselage is therefore constantly subjected to large pressure differences, “inflating and deflating” slightly with each take-off and landing cycle.
HowStuffWorks, an American general knowledge website, explains that if the window is designed in a square or rectangular shape with sharp corners, all the stress will be concentrated on those four sharp corners, creating extremely dangerous weak points. Here, the metal is prone to tiny cracks that gradually develop into large tears, threatening the integrity of the fuselage.
Plane windows look small, rounded, and seemingly just for looking at the clouds. But behind the seemingly “pretty” shape lies a story about air accidents, air pressure, and expensive lessons. Photo: Humphrey Muleba, Alex Azabache/Pexels.
The aviation industry’s most painful lesson came in the 1950s. The de Havilland Comet, a pioneering commercial jet, was designed with square windows. After a series of mysterious crashes, laboratory tests of pressure simulations found that the area around the window corners was the site of greatest stress.
According to AFAR magazine, square corners cause the surrounding metal to fatigue quickly, cracking after many flights and eventually leading to mid-air fuselage failures. Since then, square windows have been virtually banned in passenger aircraft design.
When switching to a rectangular window with rounded corners or near oval shape, the load-bearing nature changes completely. The continuous curve helps to evenly distribute the stress around the window frame, there is no longer a point of concentration of force at a sharp corner.
The rounded structure acts as a pressure “arch,” allowing the fuselage to withstand repeated pressurization cycles throughout its service life without experiencing rapid metal fatigue. In other words, the soft curve that passengers see is actually the strongest “armor” of the window area.
According to Islands.com , rounded, elongated windows are not only safer, but also make the cabin space look softer and more pleasant than square, angular windows. The light passing through the rounded frames is also diffused more gently, helping passengers feel less glare when looking out into the bright sunlight.
Today, when you walk past the window seats, few people remember the pressure tests or the Comet crashes. But each rounded rectangular window on the fuselage is the result of decades of experience and technical refinement.