Hi!

I'm trying to understand all the systems in the 737, and one thing I notice, is the window heat turning off when it reaches the correct temperature, but what is this temperature? I've tried reading and searching through the FCOM, and other sites, but there is nothing there, so does anyone know this temperature?

 

Thanks!

From my ATPL theory exams I recall it's around 35degC. Quoting from my notes:

 

As well as being designed to withstand the pressure differential and changes of temperature at altitude they must be able to withstand impact from birds. Specifically regulations state that flight deck windshields must be able to withstand impact created by a 4lb bird at design cruise speed at sea level, or impact from the same bird at 8,000ft at 85% of Vc, whichever is the more critical.

 

They are manufactured from layers of glass, vinyl and polyester materials, and bonded together to form a single laminate, where the outer layer is chemically hardened to increase resistance to abrasion from hail and dust. They are heated, not only for de-icing purposes but to prevent the material becoming brittle and to retain flexibility in the event of birdstrike. In the event of flight with window heat inoperative, the MEL will likely impose a restriction on the cruise speed.

 

Off the top of my head I cannot remember whether the heating mats are AC or DC fed, but I can tell you on good authority the windshield on large transport aircraft is often several inches thick. Bearing in mind you hear stories in the industry of geese being hit at high speed, and the carcasses have been known to smash through the radome, through the forward pressure bulkhead and take off the first officer's legs on it's transit through the aircraft, it makes you grateful for the window heat.

 

Hope you found this interesting.

 

Rgds, Olly Mylius

Wow, that was much more then I expected, and I like it!
Very interesting! Thank you so much for a quick and very good answer!