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What Is "window Heat"?

Tue Sep 02, 2003 6:02 am

Hello. Im wondering what exactly the "window heat" switches do on the overhead panel Boeing planes like the 737. Is it like a defroster?
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RE: What Is "window Heat"?

Tue Sep 02, 2003 6:17 am

The cockpit windows have heating elements in the glass. Turning them on prevents ice from forming on the glass.
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RE: What Is "window Heat"?

Tue Sep 02, 2003 8:18 am

On several aircraft as well as the role of keeping ice of the window, window heat makes the window pliable for resistance to bird strikes.

Many aircraft have airspeed restrictions when window heat is unavailable.

[Edited 2003-09-02 01:19:29]
CX Flyboy
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RE: What Is "window Heat"?

Tue Sep 02, 2003 11:40 am

Yes, cold windows become very brittle whereas warm windows have a degree of elasticity in them that makes them withstand birdstrikes better. On the 777 we always have them on and the system automatically turns them on at the beginning of a flight and off at the end. On older aircraft you have to manually turn them on or off.
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RE: What Is "window Heat"?

Tue Sep 02, 2003 9:09 pm

One of the most common problems with windshield heat is thermal shocking. Most manual systems had a two position switch; the first position turned the heat on at a low level to gradually warm the windshield up; the second position would bring the windshield up to it normal operating temperature. A lot of people (crews and mechanics) would turn the windshield heat to the high position and, in turn, reduce the windshield's life.
Later windshield heat controllers would ramp up the windshield temperature gradually and thus improved, greatly, the windshield's reliability.
If you look in one corner of the windshield, you will see the electrical grid that is the electrical connection from the power source to the windshield, usually there are two such grids, so if one goes out (which they do), the second grid provides a backup and allows use of the windshield for a longer period.
The windshield has a conductive layer between the glass and acrylic plies that heats the unit.
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RE: What Is "window Heat"?

Mon Sep 08, 2003 6:30 pm

On a sidenote: if the heating is left on on the ground, with no cooling air flow, you'll likely end up with a peculiar looking windshield...  Smile

I thought I was doing good trying to avoid those airport hotels... and look at me now.
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RE: What Is "window Heat"?

Mon Sep 08, 2003 7:28 pm

A stupid question I know but - Is the window warm to the touch when window heat is on? How hot does it get?

Statistically, people who have had the most birthdays tend to live the longest.
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RE: What Is "window Heat"?

Mon Sep 08, 2003 10:07 pm

Yes the window is warm to the touch. A normal temperature is 110deg F.
The systems have thermostats which keep the window from overheating so unless there's a malfunction (not uncommon) there's no danger to the window on the ground.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
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RE: What Is "window Heat"?

Mon Sep 08, 2003 11:15 pm

We have/had at the A/P school I used to go to a windscreen out of a 747 that had a runaway thermostat.

Yes very particular.

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