QRH: avoid icing conditions
Hi,
I was reading 737 QRH (online document) and I found this statement "Avoid icing conditions" for certain cases such wing-body overheat or bleed trip off. First I want to say I am not pilot and I don't know if this document is updated. If I am not mistaken icing conditions mean: TAT below 10C or visible moisture. Here are my questions: a) How you can avoid icing conditions? Can you predict icing conditions? Can the weather radar give you a hint about icing conditions before you enter a zone with icing conditions? b) What you will do if you can't avoid icing conditions (with wing anti ice valve closed or no bleed air)? c) What are the conditions of dispatching an aircraft if the wing anti ice valve is inoperative? Feedback appreciated. |
Stay away from visable moisture :ok:
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QRH: avoid icing conditions
...which means at nighttime, if you can see ground lights or stars and your lights aren't illuminating a cloud, you're also essentially ok.
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No the weather radar won't help you (much). Obviously you can use the radar to avoid flying through precipitation.
Otherwise you have to use common sense: E.g. look out the window. Even at night you will see when you are flying in clouds. As well you can keep an eye on outside air temperature. Engine anti-ice is still available, and the wings are not going to accumulate ice at e.g. -30 deg C. Risk of wing icing is predominantly from -10 deg to a few + deg C. And high moisture contents, which can be seen early on as small droplets forming under the wipers. A way to deal with it is not to stay in the layer with those temperatures for too long, like descending faster through it, to minimise exposure. Another way is simply to increase speed which will will increase the total air temperature. |
It's not 10C or below OR visible moisture. It's 10C or below AND visible moisture. Big difference.
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A) Avoid icing conditions by avoiding any cloud when TAT temperatures are <10C, easily done in daytime by circumnavigation, at night this may be difficult to achieve, use of fixed landing lights is an option to see a little bit ahead of you. The weather radar only is able to pick up large masses/density of moisture, thus unsuitable to detect clouds unless they contain eg rain etc.
B) If you cannot avoid icing condition you have to make a risk assessment, what is safer to do. Remain aloft or descent through a layer or possibly even land within icing conditions. All depends on fuel remaining, alternates available, weather conditions aloft and on ground... Take the lesser of the evils presented to you. C) MEL refers that dispatch is allowed with Wing Anti Ice Valve inoperative provided: Dispatching with an engine and nose cowl anti-ice valve inoperative open will cause the associated COWL VALVE OPEN light to illuminate bright and the associated thermal anti-ice (TAI) indication to also illuminate amber. Prepare the airplane for flight with wing anti-ice valve inoperative.
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Avoid icing conditions by avoiding any cloud when TAT temperatures are <10C Not really necessary if you have high negative temperatures or more than +2-3 deg C. The "less than 10 deg C" icing criteria applies to the engines due to the venturi effect of the cowling and high speed of the air passing through. You are not going to get ice buildup on the leading edges at high negative temperatures or more that +2-4 degs C. Hence you only have to avoid clouds and temp range of -10 to +5 deg C. If you have those conditions during approach = divert. Or ask for pilot reports from aircrafts ahead of you, if available. If you have those conditions (unavoidable) during descent, inform ATC about your problem and make sure to get a clearance that will let you pass the layer unrestricted (no level offs and and free speed). Personally I would reduce speed to minimum clean and wait for the Total Air Temperature to hit -20 to -15ish, then I would increase to max speed as possible according to turbulence. A 130 knots speed increase should easily give you a 20 deg bump in the Total Air Temperature and a subsequent VERY high rate of descent to minimize the exposure through the layer (use vertical speed of -6000 to accelerate faster than using level change). No need to panic. "Remain aloft" is not really a permanent solution either. :E |
I flew the A-10. It didn't have anti-ice of any kind. I flew it in the Northeast part of the US. In the winter. In cloud. We'd have ice forming on the gun, the wings, the bombs for God's sake. Anti-ice saves compressor blades (yes. We damaged them) and makes pilots feel better. Beyond that, I'm not so sure. I also flew the C-5 without wing anti-ice for hours in the ILS pattern, in winter, in clouds, never saw much wing icing. Big wing, not so much of a problem.
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QRH: avoid icing conditions
What's the relevance? Different airplane, different icing characteristics. Supercritical wing?
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