Thu Sep 27, 2001 8:24 am

When is the window/nacelle/wing anti-ice used?
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: De-icing

Thu Sep 27, 2001 8:43 am

Windshield heat (electrical) is on all the time in-flight, even in clear-of-cloud conditions. Doing so keeps the windshield more pliable (and not brittle) which comes in really handy in the event a bird strike should occur.

Engine, wing, and nacelle A/I (pnuematic) is operated only when temperature and moisture conditions exist.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
Posts: 715
Joined: Fri Aug 17, 2001 11:25 am

RE: De-icing

Thu Sep 27, 2001 2:15 pm

Let's have a short class.

De-ice is a system that sheds ice after accumulation.

Anti-ice is a system that prevents ice from forming in first place.

Pnuematic wing de-icers fall in this catagory, they don't function properaly untill a sufficient amount of ice has built up on the leading edges. If the de-ice boots are inflated too early the ice will have an elastic property that will prevent it from shedding.

Some aircraft utilize engine bleed air that directs hot air onto windscreens to melt ice away, this is also a de-ice system. Some aircraft have an isoprophol alcohol system that sprays this medium on the windscreen. Also a de-ice system, removing the ice after it has accumulated.

Some aircraft utilize anti-ice systems, this theoretically prevents ice from building up in the first place.

Electric windscreens for example, bleed air heated airfoil leading edges also.

In the case of engine inlets, never turn on engine inlet heat before engine igniters are actuated. Why, if ice builds up on the engine inlets and you turn on the anti-ice it will melt and get sucked into the engine. What happens when you throw a bucket of water on a camp fire, it goes out. That's a bad thing at 30,000 feet. If the ignitors are turned on first you have an ignition source to re-light that fire.

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