The hole serves as a bleed valve, allowing pressure between the air in the passenger cabin and the air between the outer and middle panes to equilibrate. This tiny little hole ensures that cabin pressure during flight is applied only to the outer pane.
===
SOCIAL
http://logiclounge.com
http://plus.google.com/+LogicLounge
http://twitter.com/logiclounge
http://facebook.com/logiclounge
