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This question already has an answer here:

The de Havilland Comet had pressure leaks inside the square windows which resulted in 3 incidents of the aircraft breaking apart in mid-air. A cockpit window has a similar square window and should be susceptible to pressure leaks.enter image description hereSource:(prosim-ar.com) Here is a Boeing 737 cockpit outer view. As you can see the windows are square which makes them susceptible to pressure leaks because of their square shape like the de Havilland Comet. So why doesn't the Boeing 737 cockpit windows suffer pressure leaks? And what modern methods do engineers use to reduce pressure leaks and why aren't square windows used on airliners any more?

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marked as duplicate by Simon, FreeMan, aeroalias, Ralph J, fooot Oct 13 '15 at 2:04

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    $\begingroup$ Because the engineers now know about the problems with square windows and design them strong enough so they don't leak. If your next question is "Why aren't cockpit windows round?", then perhaps they have requirements for visibility that precludes the use of windows with rounded corners. Also, see the windows on SpaceShipOne. $\endgroup$ – Greg Hewgill Oct 12 '15 at 21:20
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    $\begingroup$ Greg is right, they do have potential issues but they are understood much better with modern designs. About rounding the corners, see your related question on why they windows aren't bigger. Interestingly, new designs like the 787 and A350 also have more rounded corners. $\endgroup$ – fooot Oct 12 '15 at 21:24
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    $\begingroup$ The questions you added in your edit should be answered here. $\endgroup$ – fooot Oct 12 '15 at 21:28
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    $\begingroup$ The windows did not suffer from pressure leaks. The problem was fatigue stress cracking which led to structural failure. $\endgroup$ – Simon Oct 12 '15 at 22:26
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    $\begingroup$ That's not a 737 cockpit. It's a wooden cockpit mockup intended for a flight simulator. Be careful with the images you post. $\endgroup$ – user11516 Oct 12 '15 at 22:46
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The Comet did not have pressure leaks.

The original structure of the Comet, which had a pressurised cabin (a new technology in airliners at the time), featured rectangular windows with sharp 90-degree corners. This concentrated the stresses in the aircraft skin at these points resulting in accelerated fatigue, cracking and finally catastrophic failure of the fuselage starting at a window corner. This first happened to BOAC Flight 781

The first prototype de Havilland DH106 Comet at Hatfield.

The first prototype de Havilland DH106 Comet at Hatfield. Note the square windows.

(From the Imperial War Museum collection, public domain)

enter image description here

A later Comet 4 which now has rounded windows.

(By Ian Dunster (Own work) [CC BY-SA 2.0 uk (http://creativecommons.org/licenses/by-sa/2.0/uk/deed.en)], via Wikimedia Commons)


The photograph you have posted is not a 737. It's a wooden cockpit mock-up intended for a flight simulator. It will never be pressurised, and the builders are more concerned with the overall shape than detail around the windows.

Take a look at a real 777 cockpit:

enter image description here

(Source: Chris Sloan, AirwaysNews.com)

Notice that the corners at the ends of the widows are rounded, as are all the other corners around the window frame. There is one panel (second from left) that appears not to have this treatment. This panel can be opened (although not when the cabin is pressurised) and is built into its own frame that is fitted into the cockpit window structure. A failure in this frame will not propagate to the rest of the aircraft.

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