Hole In The Window?
Joined: Dec 2001
Posts: 941
Likes: 0
From: what U.S. calls Žold EuropeŽ
This is a venting hole.
Large transport windows normally consist of two acrylic window sheets (and a third protection sheet on the inside in the deco panel).
Each one of the two is able to stand the full differential pressure of the cabin (about 9 psi, 600 mbar). As the internal cabin pressure at cruise altitude (about 30000-40000 ft, 10000-12000 m) is somewhat lower than at sea level (normally the pressure like at about 10000ft, 3000 m), the air volume between the two window layers introduced during production would stress the outer window about 25-30% higher than the rest of the cabin structure while the inner layer would be loaded inwards.
Therefor the space between the window layers is vented to the cabin and normally the outer window layer is carrying the full pressure load.
In case of an outer window failure, a small ammount of air is flowing through the venting hole while the inner is standing the pressure load, an airflow so small the, pressurization system will not even notice it.
Additionally this venting prevents the window from fogging as it cools down rapidly at cruise altitude.
Large transport windows normally consist of two acrylic window sheets (and a third protection sheet on the inside in the deco panel).
Each one of the two is able to stand the full differential pressure of the cabin (about 9 psi, 600 mbar). As the internal cabin pressure at cruise altitude (about 30000-40000 ft, 10000-12000 m) is somewhat lower than at sea level (normally the pressure like at about 10000ft, 3000 m), the air volume between the two window layers introduced during production would stress the outer window about 25-30% higher than the rest of the cabin structure while the inner layer would be loaded inwards.
Therefor the space between the window layers is vented to the cabin and normally the outer window layer is carrying the full pressure load.
In case of an outer window failure, a small ammount of air is flowing through the venting hole while the inner is standing the pressure load, an airflow so small the, pressurization system will not even notice it.
Additionally this venting prevents the window from fogging as it cools down rapidly at cruise altitude.
