smartt1982
Topic Author
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737 Wing Anti Ice On The Ground?

Thu Jul 12, 2012 8:52 pm

I have been told that on the 737, the reason that wing anti ice (wai) is used on the ground is because of the reduced distance between the fan intake and the leading edge. Why does this reduced distance make the 737 more prone to ice accretion on the ground as opposed to other boeings were the distance between the fan intake and leading edge is greater?
 
barney captain
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RE: 737 Wing Anti Ice On The Ground?

Fri Jul 13, 2012 9:02 am

I'm not 100% clear on your question - but I can tell you with the usual caveats (at my airline and in the US), that in 20 years flying most models of the 737, I've never used WAI on the ground. The use of WAI on the ground during icing conditions does little to prevent ice accumulation on the most critical areas and in fact, will degrade the anti-ice properties of anti-ice fluid that may have been applied. The WAI on the 737 once airborne works much more effectively as a DE-icer than an ANTI-icer. We typically allow a small amount of ice to accumulate then turn on the WAI to remove the build-up. Wash, rinse, repeat   Rarely to we actually leave it on for extended periods of time while airborne.
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Tristarsteve
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RE: 737 Wing Anti Ice On The Ground?

Fri Jul 13, 2012 3:42 pm

Wing Antice will not stay on on the ground. The slats will overheat.
Most aircraft are similar, you can select WAI and the valves will open, and the leading edge will heat up then some sort of switch, usually a temp sw, will close the valves again. This normally means that WAI is on for 10 seconds or so.
Perhaps you select it on so that it starts to work as soon as the aircraft has rotated, to avoid you switching it on straight after take off.
Sometimes WAI is inhibited on the ground.
 
737tdi
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RE: 737 Wing Anti Ice On The Ground?

Sat Jul 14, 2012 5:35 am

A couple of great answers.

We, as mechs., have a hard time ops/leak checking WTAI in the summer months due to temp. control.. You may ask why are we doing it in the first place? If we have to replace a LE slat or WTAI ducting we have to leak check it, sometimes it wants to turn off so quickly that we hardly have the chance to check for leaks. Just a note...
 
vikkyvik
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RE: 737 Wing Anti Ice On The Ground?

Sat Jul 14, 2012 6:34 am

Quoting Tristarsteve (Reply 2):
Wing Antice will not stay on on the ground. The slats will overheat.
Most aircraft are similar, you can select WAI and the valves will open, and the leading edge will heat up then some sort of switch, usually a temp sw, will close the valves again. This normally means that WAI is on for 10 seconds or so.

Out of curiosity, what would be the first thing likely to fail in the event of an overheat? The actual slat mechanisms?

Quoting Tristarsteve (Reply 2):
Perhaps you select it on so that it starts to work as soon as the aircraft has rotated, to avoid you switching it on straight after take off.

What's the reasoning there? Does it affect engine thrust? Or is it just to avoid having something else to do during a critical phase of flight?

Thanks much!
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Tristarsteve
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Joined: Tue Nov 22, 2005 11:04 pm

RE: 737 Wing Anti Ice On The Ground?

Sat Jul 14, 2012 8:57 am

Quoting vikkyvik (Reply 4):
Out of curiosity, what would be the first thing likely to fail in the event of an overheat? The actual slat mechanisms?

No, the actual slat surface. The temp of the hot air in the duct will heat the slat aluminium surface up above its safe temp with no airflow present.
Out of memory, the hot air can be 200 deg C, and the max temp for the slat is around 120 degC.

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