Foggy bird strikes
From the Boeing 737NG System Handbook: “…. A conductive coating on the inner glass pane of Windows 4 and 5 permits electrical heating to prevent fogging.”
I don’t like the first option: “Stop windshield fogging up on departure when climbing into warmer air”. First of all on departure climbing you encounter cooler air, inversion exception noted, not warmer air. Secondly fogging up usually occurs after a cold soaked window is introduced into warmer moist air on descent. Information regarding windshield heat is usually found in the anti-ice system of the manuals it’s designed to keep the windows from icing over.
I was also under the impression heated windshields increase the glass’ ability to withstand a bird strike. But I can’t find that statement anywhere in the Boeing 737NG manual. The only limitation I could find in the QRH (Quick Reference Handbook) was not to excee 250 knots when below 10,000 feet for a window overheat light on condition. The speed limit was only below 10,000 after the window heat switch had been turned off. We are limited to 250 KIAS below 10,000 anyway.
If I had to choose between only those two choices I would choose the answer that links window heat to anti-ice function, but that is not given it’s “fogging” or “bird strikes”. Because my Boeing 737NG System Handbook does mention, “fogging” I would reluctantly have to go with the first option even though I don’t like it.
Last edited by Northbeach; 12th Jan 2010 at 04:59.