Why aren’t plane windows square? Experts explain the simple but crucial reason for it

Have you ever noticed that plane windows are always oval shaped and never square?
It is probably something many fliers will have never stopped to consider – but a recent engineering video explains just why it is so vital they have their current shape.
The simple yet important explanation is that dangerous levels of stress build up on the corners of square windows. A round window drastically reduces the chances of pressure building up.


The video, produced by Real Engineering, uses diagrams to explain the flow of pressure through the cabin during a journey and show the points of a window that would have increased areas of strain.

Dai Whittingham, the Chief Executive of the UK Flight Safety Committee explained to MailOnline Travel: ‘Square corners concentrate the stresses and can lead to fatigue failure of the structure.

‘Designers prefer oval windows because they can get a larger viewing area which suits the biggest range of passenger sitting heights.

‘The narrowest part of the oval will be designed to ensure the curve does not generate unsafe stresses in the surrounding material.

‘Recently we have started to see some designers opting for more rectangular shapes, but these will always have curved corners.’

Early jets featured windows of a square design and designers only realised this scientific flaw after it was too late.

This was tragically seen with the first commercial jet, the de Havilland Comet, which saw a plane disintegrate mid-air in 1954.

The aircraft had square windows and an accident investigation discovered that one of the windows had been the source of a structural failure that killed everyone on board.

The pressure differences inside and outside the plane had caused the fuselage of the aircraft to expand slightly, and with the temporary expansion, the jutting corners added to the stress.



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