As passengers planes became more popular now days , plane need ti fly higher higher means less drag because air density is lower in upper atmosphere means more comfortable flight because the plane can now fly above turbulent level .
The pressure between inside plane and outside of plane is totally different and if outside pressure came inside of plane then then flying smoothness of plane will be uncomfortable and plane will starts to fall down or crash .
This will only happen when there is some leak in plane
If we place square windows in plane then the flow of air will be like this ⤵️
Then, if window shapes is circle then the air flow is smooth and plane can fly without any distrubance .
And if plane window are square then the result will be crash. this is photo of crash happen before few years ago when plane architectures are using square window in plane .
