Ice bridging: it happens

ZeroPapaGolf

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ZeroPapaGolf
Recently the NTSB has been pushing their documentation regarding ice bridging, specifically that it does not happen in turboprop aircraft, and that pilots should use deicing boots at the first trace of ice. That may work great in a modern turboprop aircraft, but its simply not true for (some?) older piston twins.

Today's flight was a great example if that. Moderate rime icing and occasional freezing rain at 10,000' (-7 Celsius). I decided to test the theory and popped the boots with less than 1/4" accumulation. Some came off, but the majority flexed away from the boot and stayed attached. Activating the boots again did not move it further. After allowing a more substantial accumulation to form, the boots easily cleared all the ice.

We're going into summertime, so this shouldn't be an issue much longer (though this is the mid-south in May and I was still finding a ton of ice, so it can happen anytime until its truly summer). It seems like the best course of action is to do as I did today, and see just how your aircraft handles shedding ice. Today was the perfect conditions for it as well, as above-freezing temps were at 8k, and tops at 11k, so escape was guaranteed if necessary. Aircraft: PA-31-310.
 
In the Duke I was taught to not even think about popping the boots until you've lost 10 kts of airspeed or you'll get bridging you can't clear.
 
That's not "bridging". If it was you would not have been able to clear it later. You're just seeing pieces of broken ice sticking to the boots. That's normal when you pop the boots more frequently. One of the spray on chemicals will help shed better.
 
Ya, pretty much what Jeff said. Modern boots (in the past few decades) have a pleated surface. Each boot is made up of several tubes giving it a "rub board" look when inflated. These boots will not bridge. Many years ago some boots were just one big balloon. It was possible in some conditions to expand a layer of ice out to the shape of the boot and not break off. I do not have any experience with these boots other than pilot talk and a few pictures.

I am not aware of any boots made this way now. The ice you see sticking to the boots in some places can be made less of a problem with good boot treatment. I,for one, in the last plane I flew seldom had to use the boots but, I kept them maintained with a product like boot shine. A slick well maintained boot (no pin holes or other leaks) will shed ice pretty well. Of course speed is a factor also.

Personally, I prefer to see a little ice build up before inflating the boots, I do believe they shed cleaner. But that is just me. YMMV

Ronnie
 
I'll have to give the the boot shine a shot. Thanks.
 
A side note:
1. When using a product like Boot Shine, follow instructions to the letter. Temperature is important. I suggest greater than 70 deg when applying.
2. The prep procedure is VERY important.
3. When applying I suggest a terry cloth about the size of a normal wash cloth. Fold it to an approximately 5 inch square. Start at one end of the boot and go all the way in one motion. Make sure you have enough product on the cloth to go all the way. Start back at the end and repeat until boot is covered. Give about 10 minutes between coats and you will need 3-4 coats on boots that have not been treated.
4. Did I mention to follow instructions exactly?

Ronnie
 
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