The Reason for Round Windows: The De Havilland Comet
After World War II, air travel began to boom. In the early 1950s, one of the most conspicuous airliners was the De Havilland Comet, the first jet airliner in the world [1]. Much as jet fighters had quickly outmoded their propeller-driven predecessors, the Comet redefined air travel with its four jet engines and sleek design. Unfortunately, its short career was quickly marred by a couple of dramatic and deadly accidents.
Figure 1: An early prototype of the De Havilland Comet [2].
The History of the Comet
The Comet was much faster than prop airliners, cruised at 30,000 feet, and carried tens of thousands of travelers in its first year of service. Designed and produced in the United Kingdom, one of the maiden year travelers included Queen Elizabeth [3]. Regrettably, 1954 saw the disintegration of two Comets midair, resulting in the deaths of 56 passengers between the disasters. Post-crash analysis unveiled the fact that the accident was a result of a stress concentration caused by the plane’s rectangular windows.
During flight, an aircraft transitions from a higher-pressure air region near the surface of the earth to a low-pressure environment at a higher altitude. Undergoing this pressure change twice per flight adds up, and such consistent fatigue stress concentrated in the corners of the rectangular windows as the Comet accumulated hundreds of flights. Analysis determined that up to 70% of the fatigue stress was focused in the four window corners, leading to cracks and, in the two instances mentioned above, catastrophic failure [4].
Figure 2: A rounded window in a modern airliner [5].
Rounded Windows and Cascading Effects
Because of the lessons from the Comet, modern airliner windows all have rounded corners (There once was a craft with triangular windows, though [6]). These lessons learned in aircraft design cascaded to other technologies. The same design is mirrored in the portals used in space and oceanic design. Although rectangular windows were first used because they were simpler and more analogous to home windows, safety has dictated change [5].
While engineering failures are destructive and often heartbreaking, they can be fundamental to making important design changes. All design failures can lead to improvements. Still, failures can be mitigated by approaching design slowly and thinking through each aspect. While many lessons can be learned from nature, things like rounded windows are less intuitive because there are no creatures that routinely soar to airliner cruising altitude before coming back down to earth. At the end of the day, failure is one of the most consistent opportunities for process improvement.
Figure 3: A diagram that showed the process of flight failure for BOAC flight 781 [7].
The Most Important Takeaway
Because no materials have infinite strength, any structure has the possibility of failure. As such, engineers plan on failure and even design specific failure points to ensure that failure occurs in a non-catastrophic manner. A catastrophic failure occurs when a structure is compromised to a point in which it is rendered useless . A failure of this sort is often accompanied by death or serious injury.
The lesson of the Comet illustrates how engineering design must take into account all possible modes of catastrophic failure. Fortunately, there are systematized approaches to thinking through designs and catching weaknesses in the design. Modern air travel is not without its hazards, but modern aircraft designers have implemented numerous redundancies and strategic failure points to maximize safety.
References
[1] "Comet – the World's First Jet Airliner." Royal Air Force Museum, 2021, www.rafmuseum.org.uk/research/archive-exhibitions/comet-the-worlds-first-jet-airliner/.
[2] Admiral Cloudberg. "Neither Money nor Manpower: The Story of the De Havilland Comet and the Crash of BOAC Flight 781." Medium, 12 Mar. 2023, admiralcloudberg.medium.com/neither-money-nor-manpower-the-story-of-the-de-havilland-comet-and-the-crash-of-boac-flight-781-36db2a3435ce.
[3] "Why Airplane Windows Are Round." NCI, 8 Aug. 2022, nci.edu/2022/08/08/why-airplane-windows-are-round/.
[4] "Why Aircraft Have Small Round Windows." Simple Flying, simpleflying.com/why-aircraft-have-small-round-windows/.
[5] "Why Are Airplane Windows Round?" Reader's Digest, RDA Enthusiast Brands, www.rd.com/article/why-airplane-windows-are-round/.
[6] "The Real Reason Airplanes Have Rounded Windows." AFAR, www.afar.com/magazine/the-real-reason-airplanes-have-rounded-windows.
[7] u/AdmiralCloudberg. "1954: The Story of the De Havilland Comet and the Crash of BOAC Flight 781." Reddit, r/CatastrophicFailure, 18 Mar. 2023, www.reddit.com/r/CatastrophicFailure/comments/11uv40y/1954_the_story_of_the_de_havilland_comet_and_the/.
To cite this article:
Conover, Dylan. “The Reason for Round Windows: The De Havilland Comet.” The BYU Design Review, 15 Jun 2026, https://www.designreview.byu.edu/collections/the-reason-for-round-windows-the-de-havilland-comet.
