Question: How dangerous is a cracked cockpit windshield? When is it most likely to happen (takeoff, cruising altitude or landing), and what can be done about it?
Answer: Cockpit windshields contain two panes of thick glass with a plastic layer in between for heating. Either pane is capable of holding full pressure if the other is lost. Typically, a heating problem will cause the outer pane to crack, and the spiderweb will progress.
The side windows in the flight deck are similar to the windshields. While not quite as thick, either pane can hold pressure if necessary.
In my experience, windshields are more likely to crack while climbing than in other phases of flight. However, I know several pilots who have experience cracked windshields at cruising altitude.
Cabin windows are a bit different. They are plastic and not subject to air or structural loading. While there is an inner pane, it is thinner and not as strong. Consequently, they are not as robust. On the upside, window cracks typically do not progress like they do on windshields.
Airplanes are designed to remain safe if a windshield or cabin window cracks. While this does happen occasionally, it is infrequent. Pilots will descend to reduce the pressure and plan on a diversion if necessary.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
This article originally appeared on USA TODAY