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737NG anti ice /Emergency Descent

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737NG anti ice /Emergency Descent

Old 1st Jun 2014, 01:54
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737NG anti ice /Emergency Descent

Hi,
The memory items for an Emergency descent include the sentence
"Reduce thrust to minimum or as needed for anti-ice"
I can't find a reference in the FCOM or anywhere stating what the minimum N1 is with either Engine or wing anti-ice on.
Can anyone point me in the right direction?
Thank you
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Old 1st Jun 2014, 02:21
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Check out High Engine vibration NNC

Normal N1 flight idle is OK for most ice events.
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Old 1st Jun 2014, 02:24
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I believe Some MEL procedures require higher minimum thrust settings(N1) for anti icing operations.

If you operate with said MEL restrictions in icing conditions then you would have to comply with the higher minimum thrust setting, even in emergency descent.
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Old 1st Jun 2014, 02:41
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The Classic has a DDG MEL restriction of 60% N1 for ice operations with the 9th stage bleed valve locked closed.
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Old 1st Jun 2014, 05:37
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Framer, no specific knowledge about the 737NG, but on the current Boeing wide-body airplanes, selecting engine anti-ice will automatically give you "approach idle", which will provide sufficient bleed pressure for engine and wing anti-ice.


I "believe" the 737NG works the same way, but I don't "know" that it works the same way.
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Old 1st Jun 2014, 06:15
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FCOM SP16 directs you to increase N1 to 30% if engine cowl anti ice lights stay bright, ie the anti icing not working properly. (B737NG)
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Old 1st Jun 2014, 08:31
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As mentioned for the classic, the NG retains the requirement for 60%N1 in icing conditions with the 9th Stage INOP'd.

I took an aircraft with this fault a week or two back. Also limits the Aircraft to CAT I as the A/T is inop.
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Old 1st Jun 2014, 08:34
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Brilliant. So if there was a restriction you would know about it from the MEL.
Thanks for your help.
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Old 1st Jun 2014, 12:37
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Low Idle produces the bright blue lights, you mainly see it for Wing Anti Ice on the ground with low power settings. So im guessing its enough N1, so you dont see the bright blue lights (Anti-Ice Valve operation is pnuematic from memory) Try turning on the Anti-Ice on ground with out the engines operating and youll see what I mean
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Old 1st Jun 2014, 13:20
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Wing Anti Ice on the ground turns on or off depending on temperature though, not depending on N1. Idle is normally sufficient on the ground to keep both engine anti ice and wing anti ice operating. The cowl anti ice valves are electrically controlled but pneumatically operated (simply by bleed pressure). Wing anti ice valves are however AC operated.

As Jwscud mentioned any requirement for more than approach idle in flight with anti ice on is triggered by operating according to a MEL item as far as i know.
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Old 1st Jun 2014, 23:26
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But Denti, if you increased N1 on ground, The bright blue lights for Wing Anti Ice go dim! So it is somewhat dependant on N1
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Old 2nd Jun 2014, 00:04
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Note: The wing anti-ice VALVE OPEN lights may cycle bright/dim due to the control valves cycling closed/open in response to thrust setting and duct temperature logic.
The above from our FCOM.
I always thought it was just from temperature but the above statement seems to back up Wang's statement.
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Old 2nd Jun 2014, 06:15
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But Denti, if you increased N1 on ground, The bright blue lights for Wing Anti Ice go dim! So it is somewhat dependant on N1
You have it backwards, if the thrust levers are advanced on the ground with wing anti ice on , the dim blue lights go bright because the valves are closing and are no longer in the selected position.
The switch/light logic is:
light off-switch off and valve is closed
light dim- switch is on and valve is open
light bright-switch and valve position disagree or valve is in transit.

The wing anti ice valves are electrically activated/driven (as Denti pointed out). When on the ground there are two things that will automatically shutoff the wing anti ice.
Overheat protection via overheat thermal switches in the L/R leading edges. If either switch is triggered at 257F the valves in both wings will close.
If the thrust levers are advanced, switches in the autothrottle switch pack close and send a signal to close the anti ice valves. This is done to conserve engine power for takeoff.
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Old 2nd Jun 2014, 14:50
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The wing antice bright disagreement lights appear when on the ground(EAI/WAI selected ON but valves closed) if wai duct temp get above 125 C despite max ground cooling and /or if thrust lever angle above 35 degrees.
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