Little Mistakes from History With Huge Consequences

A de Havilland Comet with square windows. Raschofield Collection

19. Why Passenger Airplanes Have Round Windows

Boeing has been the dominant player in passenger planes for the bulk of the commercial air travel era. However, there was a time in the early 1950s when reasonable people could have predicted that the future of passenger planes belonged to Britain’s de Havilland, with Boeing a distant second. The reason was the de Havilland Comet – history’s first commercial jet liner, whose prototype first flew in 1949, and that hit the market in 1952. Fast and sleek, with a pressurized cabin that was comfortable, relatively quiet, and featured large square windows, the Comet cut six hours of travel time between London and New York. It was the world’s most promising passenger plane when it made its debut.

The Comet’s designers opted for large, square windows, because of aesthetic reasons: they looked better than the traditional round “porthole” style windows. Unfortunately for de Havilland, and for dozens of Comet passengers who died in a series of crashes, designers back then did not understand metal fatigue. Stresses piled up at the corners of the Comet’s square windows, causing catastrophic fuselage breaches mid flight, resulting in fatal crashes. Since the Comets often broke apart high altitudes and above water, it took time to figure out the problem. Once they identified the culprit, the entire Comet fleet discontinued service. De Havilland never recovered: while the Comet boasted a new design with round windows and thicker fuselages, the Boeing 707 and Douglas DC-8 hit the market, and became hits with airliners.