Ice Bridging-Myth or Reality?

Knob

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I was flipping through the new AOPA mag. and noticed an aritcle on icing which stated "researchers have learned that ice bridging is a myth." Maybe the researchers weren't ever able to produce bridging in a controlled enviornment, but I've seen and experienced it first hand on the E-120. The wings were OK, but after landing I noticed the whole tail had a "Bubble" of ice where the boots had been inflating & deflating. I wish I'd had a camera for that one. I don't care what the FAA says, I've seen it and wonder if any of you have similar stories?
 

GravityHater

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Its true -FAA says its rare or not worth worrying about. Supposed to turn on the boots at first sign of ice.
 

OPECJet

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Bullsh!t.... I've seen it happen.
 

CA1900

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I've seen it as well in the Beech 1900. Blowing the boots at the first sign of ice is about the worst possible thing to do in this airplane. Maybe it varies from model to model, but as blanket advice, that's dangerous.
 

WSurf

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Yea, when I was at Commutair... many of the captains would bug the airspeed at cruise! Once you started seeing the speed drop 10-20kts you would slap the boots on... and watch the speed increase again. It was pretty cool to watch. I still use that techn. at PDT in cruise with moderate icing, even with everthing done automatic in the Dash, it nice to keep an eye on that speed in cruise.
I think ice bridge depends on factors of type of ice, accumulation time,... But I think with most of the newer boots its not a real factor anymore! Atleast not in the Dash 8. Beside the 1900D (Which is a man child in ice... Its boots are great, and the plane has some powerful engines. I have landed with that thing looking like a glazed doughnut) the dash handles ice really well.
 

erj-145mech

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Pneumatic boots are not an anti ice measure, they are a de-ice method. Engines, props and windshields are supposed to be on continuously. Unless you have mass quantities of bleed air or TKS fluid, wings and tails off untill you have a build up. Thats what the manufacturer recommends. The people that built it have precedence over what the feds say.
 

acaTerry

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The two post that precede the one am writing now pretty much sum it up. Also, keep in mind the FAA icing tests used SLD of a much smaller size than we typically see in real life.
 

rattler

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I've had it too in a PC12, which has a fairly modern boot system.
 

SkyWestCRJPilot

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On the Brasilia the FAA and Embraer require the boots to be on while in icing conditions. Many tests were done on the EMB-120 after various crashes and incidents because people were doing this exact thing, waiting to let the ice buid up. That is what killed them. The test determined that as soon as you enter icing conditions you turn the boots on and leave them on as they automatically cycle. There have been hours and hours of testing done on this type of thing by trained test pilots and professionals. Don't let some anecdotal evidence convince you otherwise. Any residual ice that remains is either insignificant or will shed itself soon. Ice bridgeing originates in the DC-3 era airplanes where the boots took a long time to inflate and did so under low pressure. Modern transport category aircraft have quick inflating boots at high pressure so ice bridgeing isn't an issue. If you are in severe icing conditions and still losing airspeed and performance with the boots on you are in SLD (supercooled large droplets) and you need to exit immediatly. Don't confuse that with ice bridgeing.
 

Tim47SIP

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Roselawn!

This exact thing contributed to the ATR 72 crash in Roselawn. I have pictures from the NTSB that showed ice bridging on the defective system that the ATR's use to use. Additionally, the ATR accident was also caused by formations of ice behind the effective area of the boots. The ice eventually built up to a point that the boots couldn't clear the ice on the leading edge and bridging occurred. So you guys are correct, it can and does accrue!
 

P-Dawg_QX

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LOL....I came into this thread expecting to see a discussion on how the first humans got to North America.

Don't worry about me, I'll just be over here...committing myself to the insane asylum.
 

TIGV

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Actually Roselawn was the result of holding in moderate icing conditions in a configuration not approved for ice penetration.
My feeling is if you're in ice, GET OUT ! My boots are there to provide me time to do so and the last thing you will find me doing is holding in moderate ice .....especially in what I'm flying in now.
Your job is Safety above all.
 

SkyBoy1981

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P-Dawg_QX said:
LOL....I came into this thread expecting to see a discussion on how the first humans got to North America.

Don't worry about me, I'll just be over here...committing myself to the insane asylum.
Nah, just shows that you're actually capable of thinking beyond aviation. ;)
 

shamrock

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P-Dawg_QX said:
LOL....I came into this thread expecting to see a discussion on how the first humans got to North America.

Don't worry about me, I'll just be over here...committing myself to the insane asylum.
Don't know if it helps, but I thought the same thing as well.
 

LowlyPropCapt

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shamrock said:
Don't know if it helps, but I thought the same thing as well.
Actually, they came across on a land bridge, not an ice bridge. At the end of the last ice age, the volume of the ocean was sufficiently low enough to create an area of land between present day Siberia and Alaska.

End of Know-It-All coment of the day!

By the way, I don't remember hearing that Roselawn had anything to do with bridging. I thought that had everything to do with holding in severe icing conditions with SLD of a size that no aircraft is certified for. Personally, I have ever experienced any sort of bridging.
 
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mckpickle

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I don't think Roselawn had anything to do with Ice Bridging. They were holding at less than 185 knots. (The 72 gave a overspeed warning at 185 for flaps 15) They were holding in conditions worse than ever recorded with regards to inflight icing. Anyone who's flown a 72 know that the pitch attitude at 170 is pretty high, even with flaps 15. (I say 170 because I think that was the max holding airspeed at 8000msl when the crash occured). The bottom line here is they never should have been in those conditions. With that amount of accretion the a/c was way beyond it's capabilities.

I'm not sure about the systems on the 120 or the 1900 but the ATR, (which BTW had more ice testing than any a/c in history) you just set the boots to on and let them cycle. I've never seen the boots blow under the ice. Even in severe icing the boots blew it all off and didn't do it to often to let it build underneath. The Comair crash that everyone is refering to resulted in manditory ice detectors being placed on the 120. Before the crew had to see the ice and turn it on themselves. If ice was accumulating but the crew didn't see it than they wouldn't blow it off. I'm not saying bridging can't happen but with the boots we're using today it pretty darn unlikely if you use it as prescribed.

I'll still take the ice over the thunderstorms:nuts:
 

r1830

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As a First Officer flying both the Twin Otter and Dash 8 in Alaska I have seen some icing. 99.9% of the time the de-ice boots have worked great, but I have had ice bridging occur once. In most icing test the boots are in great condition. I think a major factor in ice bridging is the condition of the de-ice system. Fly an aircraft that has a couple of patches on the boots, has not been ice-xed in a while and dirty boots the ice seems to stick to it.

We were flying a 200 Series Twin Otter(less power than the more prominent 300 Series) from Bethel to Anchorage over the Alaska Range. It was late spring, early summer and the leading edge was covered with a combination of old deice fluid, dirt and bugs. The MEA between Sparrevohn (SQA) and Anchorage is 12000 feet and a MOCA of 10,300 feet. The 200 series Otter is usually temp limited or at the stops at altitudes above 10,000 resulting in torque settings around 37 or 38 pounds of torque. The outside air temperature was around -20 Celsius. We got into some light rime ice just past SQA at 13000 feet and cycled the boots (to early?) with ice estimated at around 1/8 to 1/4 inch. The boots inflated but most of the ice did not shed. We decided to let it build up a little more ant try it again. This time with a little more than a ½ inch of ice we cycled the boots with the same result. Climbing was not an option so we descended to 11,000 feet and continued to cycle the boots with out any real improvement. Although there seemed to be less icing at that altitude. We were in the ice for about fifteen to twenty minutes before we could descend to 6000. By that time we had accumulated about 1 1/2 inches of ice and slowed considerably. Once in the clear and with a head of steam in the descent we started shedding the ice as we descended through about 7,000 and the temperature was still below freezing. The boots seemed to be working fine after we exited the icing condition and got into warmer temperatures. I don’t know why we couldn’t shed the ice. I think part of it may have been the condition of the boots.

The incident above happened before we changed our Ops Specs in accordance with the FAA’s new recommendation. In both the Twin Otter and the Dash 8 our ops specs now have us activate the boots upon entering icing conditions. We leave them on until at least one complete cycle has been performed after exiting icing. I have not seen “ice bridging” occur since implementing these procedures. But I have seen more residual ice on the boot after the first cycle or two. But the end result was the boots were able to keep shedding most of the ice and not allowing it to build up. I must admit though I am not totally convinced that this procedure will prevent ice bridging.

On another note, climbing out of Kodiak last week we got into some freezing rain at -15 Celsius. That is the coldest temperature I have ever seen freezing rain. The cloud didn’t look threatening and the weather radar barely showed some green.
 

CFIse

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r1830 said:
We were flying a 200 Series Twin Otter(less power than the more prominent 300 Series) from Bethel to Anchorage over the Alaska Range. It was late spring, early summer and the leading edge was covered with a combination of old deice fluid, dirt and bugs.
What you described was boots with the inability to shed ice - but that's not ice bridging. Ice bridging is when the boots "push" the ice out so that it forms a shape around the boots and continues to build. Subsequent inflations of the boot occur in the space between the wing and the ice - the ice has "bridged" the boots.

With modern boots bridging is a myth - I'm not old enough to know about older boots - maybe they could bridge.
 

r1830

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CFIse
What you described was boots with the inability to shed ice - but that's not ice bridging. Ice bridging is when the boots "push" the ice out so that it forms a shape around the boots and continues to build. Subsequent inflations of the boot occur in the space between the wing and the ice - the ice has "bridged" the boots.
Sorry, I didn't explain the second activation of the boots correctly. Let me expand on that a little.

R1830
The boots inflated but most of the ice did not shed. We decided to let it build up a little more ant try it again. This time with a little more than a ½ inch of ice we cycled the boots with the same result.
At the second activation of the boots some inflation was noticable but lacked in cleaning the wing. We left the boots in auto/fast and after a couple of cycles boot inflation could not be seen. This may or may not have been ice bridging. We could not see if there was an air pocket between the ice and the boot. But, the end result was the same, we could not shed the ice till we were in a descent descending into warmer air in the clear. The boots were inflating after the wing was clear of ice.
 
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