Depending on the cracked layer, there would be some actions from the crew. The inner layer seems to be simple to identify, but if the middle and/or outer layer is cracked, how will pilots identify the right crack's position?


1 Answer 1


It is possible to identify whether the crack affects the inner layer by sliding over it with nail or something sharp like pen. If the layer is cracked, the slight indenting in the surface can be felt.

As far as I can tell, there is no way to tell whether the outer or middle layer is affected with any useful degree of certainty. It is also not possible to ascertain how many layers are cracked. So usually the procedure is so that if the inner layer is not affected, you can continue and fix the issue at destination and if the inner layer is affected, you have to conservatively assume all layers may be affected and descend.

  • $\begingroup$ Shouldn't it be fairly easy to tell whether all the layers are cracked versus just the inner layer, by listening for the noise of air whistling out through a full-thickness-cracked windscreen and/or checking whether the pressurisation system is suddenly having more difficulty keeping the aircraft pressurised than it was pre-crack? $\endgroup$
    – Vikki
    Commented Mar 13, 2019 at 21:45
  • 1
    $\begingroup$ @Sean, I don't think there will be any significant airflow through a crack. Certainly not to either hear it over all the other noise in the cockpit and even less so for the pressurisation to be affected (the outflow valve is quite big opening, even a hole in the window would be small compared to it). $\endgroup$
    – Jan Hudec
    Commented Mar 14, 2019 at 9:01

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