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What sorts of things hit airplane windows while flying?

You've heard of bird strikes on planes - specifically on their engines causing engine failure and crashes.  But a question came to me - what sorts of things crash into airplane windows - especially those necessary for pilots?  I decided to look it up on the internet.  Here's what I found.

• Bird strikes are a major problem, not only for engines but for cockpit windows too.  Complete failure is uncommon due to their strong design, but any damage can cause depressurisation at high altitudes.  Fortunately, most bird strikes occur at low elevations.
• Although it is unlikely for insects to cause significant visual obstructions on pilot windows, they can foul up air speed indicators through building nests inside instrument intakes.  Mud daubers have been known to impair airspeed indicators this way.
• Hail is known to cause pitting and damage to aircraft, but modern design prevents it from being catastrophic.  There is an interesting photo/story on the subject here.
• Foreign objects that may be kicked up during takeoff and landing may also cause cockpit window damage.  On poorly maintained aircraft, there is the risk of components of the plane coming off and striking the window.
• Lightning is not likely to cause physical damage to the windows, but can leave scorch marks.
• Repeated thermal and pressure stress can, over a long period of time, cause windows to be more subject to cracking or breaking down altogether.  

Aircraft that serve the public have frequent checks to ensure that all components, including the windows, are in proper condition.  Walk-arounds by the pilots, regular maintenance checks, and detailed C- and D- checks (once every 1.5 years or 6 years) monitor the condition of the airplane.

The truth is that it is rare for a pilot's window to fail, given its design and frequent checks.  Isn't that interesting?

Thanks for reading.

Eric Svendsen     www.ericspix.com