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As350 Fx Ii Aerofilter Clogging

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It's that time of year again, recurrent exams. Every year the same question is asked regarding a clogged air filter in falling snow. Every year the answer is the same. Yet I would like to know why I can't open the doors in blowing snow?


To put it in context, I have flown a 350 D quite often in heavy snow, within visibility limits, with no filter and have never run into a problem. Both with the 101, and 600 engines.


The only things I can come up with is:

1) There was associated laminar ice build up along the fuselage of the a/c during testing that could fly into the by-pass orifices during testing.


2)That the orifice of the by-pass system is such that it creates a venturi and would create ice out of the heavy snow fall to such an effect as to cause engine failure.



Basically, what I would like to know is if my filter clogs in flight in snow, "What do I have to lose by opening the bypass doors"?


Btw...anybody actually had a clogged filter in snow that was clean prior to flight?


Thanks for your input.

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If snow is already packed/blown in to the area below the filter where the doors are located and then you open the doors then a slug of snow could be drawn into the engine and flame out. Snow itself is not usually an issue unless it is swallowed in big gulps or is wet sloppy stuff.


Had issues with one filter light coming on in cold snowy temps after it was cleaned. Turns out that the filter had not completely dried prior to oiling thus in cold the water in filter became ice and thus became a clogging agent. Even though the filter had sat in hanger for a few days it was not warm enough to dry out. The crew took the filter into tent at night for a few nights and was dried out. These filters can dry in hours in warm summer day but not so in cool temps. I cleaned one the other day and water formed a puddle for almost two days on a heated cement floor.


good luck!

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I had an AFS filter clog on a B2 last December in very fine, dry falling snow while long-lining (high power, 40kt). The light would come on, but no degradation in engine performance (T4, Ng, Tq). As soon as I was out of the snow, the indicator extinguished. Inspection before next flight showed no clogging or filter degradation. I called it in and was told to monitor my params, that because it was such fine snow, it could be an indicator problem rather than actual clogging.

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"If snow is already packed/blown in to the area below the filter where the doors are located and then you open the doors then a slug of snow could be drawn into the engine and flame out. "



How are you getting snow past the filter if the doors are closed?

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Irrespective of the "rules", for when and when not to open the bypass doors, the warning light is set up on a differential switch that, by intent, is set well below the point where actual restriction to airflow, that would adversely affect the engine, would occur. If the light comes on (I have had it with an AFS filter in falling snow the size of rabbit skins, after sitting on the ground running for a few minutes...) but all other indicators are normal I wouldn't panic. I have landed on several occasions just to make sure everything was fine and the light has gone off by itself after a few minutes at flight power... I would not open the doors in snow unless the numbers I was looking at (T4, Ng, etc) seemed incorrect, and by the time you'd make that decision you could have already landed 99 out of 100 times.


Land first ask questions later!



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