Ice accumulation/Boots

Simon Says

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OK everyone what is your take on this, and if you fly a Saab 340 what does your company wants you to do.

After NASA did their ice testing in a twin otter they discovered ice does not bridge on boots anymore. They found that todays technology in boot manufacturing minimizes the chances of bridging; and because of that our company came up with a new policy on how to function our boots in ice.

On the Saab we have two choices to operate our boots. One Cycle, or continuous. One cycle inflates the stabilizer, outboard wing, inboard wing, stabilizer. With continuous on it does one cycle every three minutes.

After the NASA study our company now wants us to operate our boots in continuous mode if we are in any ice. After following this procedure I found that in light ice I never get a good break.

The only way I have found to get a good break is let the ice build to mabey a 1/2 of inch then give it a one cycle. This is of course dependent on the type of ice too. Clear ice gives a better break than Mixed or rime ice. I think that is because of the air bubbles that are in the rime and mixed ice.
 

Saabslime

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If I'm in icing conditions for an extended period of time I use the continuous mode. Usually get a good break about every other cycle. The hard part is remembering to turn the **CENSORED****CENSORED****CENSORED****CENSORED** things off inside the marker. Otherwise I just use one cycle if enough has built up to make it worth the effort.:D
 

AWACoff

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At Lakes, we were required to have all of the ice protection on any time we were in "icing conditions". That doesn't mean ice is on the airplane even. It is typically defined in your Ops manual. No Brasilia I was ever in crashed and that's how I made sure the airplane was flown. I've never seen ice bridge on the E120 or Doinker.
 

avbug

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I can't comment on bridging on the saab or brasilia, but despite the FAA's latest input on ice bridging, it does happen. I've had it happen, and I have no doubt a lot of other folks here have, too. The FAA hasn't provided the recommendation for continuous operation based on the fact that ice briding doesn't occur. It does. It absolutely does. However, the general consensus is that it's better to take the risk (and a reduced risk with some newer designs) than to be placed in a situation where the ice cannot be broken. It's also better to remove an accumulation as early as possible.

The concept of allowing ice to form and then break off risks being placed in a situation where ice builds quickly and cannot be broken, or builds and cannot be removed due to boot/blanket/bleed/pump failure. In such a case, it may be too late to do anything. On the other hand, if ice is removed early, or the attempt is made, there may be early warning before continuing farther into icing conditions. If an attempt is made to remove ice and the system doesn't work, it's far better to know this early, than to wait until a healthy layer of ice is built up.

The recommendations from the FAA dont' stem from a lack of bridging, but are based on a general rule to take into account pilot error and human nature. More of a one-shot fixes all, recommendation.

Additionally, as ice builds on the boot, lee ice forms behind the buildup, and cannot be removed by the boot. As the boot breaks the ice, the ice aft of the boot continues to disturb the boundary layer and provide an aerodynamic degradation, and may continue to allow an accumulation aft of the leading edge and boot area. This doesn't always happen, and often this ice comes off with the application of boot pressure, but not always.

The newer (kinder, gentler) approach from the FAA is a catch-all that I believe is more intended to idiot proof de-ice sytems, than address the latest in technology (which still bridges, incidentally).

Some boots with high frequency pulsations tend to dispell ice when used continuously; there is very little buildup, or a chance of buildup. Such systems are best used continuously, but this should be on the advice of the manufacturer. As with all systems, the direction given by the manufacturer should be the overall guide, coupled with your own experience and observations.
 

Prop Trash

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Originally posted by AWACoff
At Lakes, we were required to have all of the ice protection on any time we were in "icing conditions".
I find that odd. I know different operators have different policies, but my old BE-1900 manual (COEX) states "For most effective leading edge deicing operation, allow at least 1 to 1-1/2 inches of ice to form before attempting ice removal... subsequent cycling of the boots will then have a tendancy to build up a shell of ice outside the contour of the leading edge, thus making ice removal efforts ineffective."

Just to provide a different view point, when entering level 2 icing conditions (OAT +5 degrees and below, visible moisture), we were only required to use auto ignition, engine anti-ice, windshield heat, prop de-ice, and the level one items - fuel vent heat, stall warning heat, pitot heat, and alternate static heat.

For the Lakers out there, how well did your procedure work? I always found the Beech to be a terrific ice-hauler. Anyone have any scary ice stories from the Beech? I fly the ATR now. It's all together a different story.

P.S. AWACoff, I just noticed you flew the 120. Disregard this message.
 
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Twotter76

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I'm going with Avbug on this one. I fly a Twin Otter and let me tell you, ice bridging is a very real concern. I've no idea how the FAA came to that conclusion using this airplane. Granted it carries ice very very well but turn those boots on too early and you are screwed. We use a procedure similar to what the previous poster described, we wait til there is at least 1/2" then we blow the boots, usually just once but if are near the final approach segment we will turn them on and just let them cycle to landing. I am going to recheck it but I do not believe our ops specs have an established procedure for ice removal in-flight, it's PIC's discrection.

Twotter76
 

Cornelius

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When I was training with Lakes in June, they were teaching me to blow the boots when there was 1/2 - 3/4 inch of ice on the leading edge or if there was a 10-20 kt decrease in KIAS. I was just trying to look for the exact numbers in the Flight Standards Manual and couldn't fine em' so these figures may be bit off. The figures may have changed since July since I don't get the revisions any more.
 

mar

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An elaboration of "Fly the plane"

Everybody's made some good points, especially Smoking Man and Turbo S7.

The bottom line is that the PIC is the final authority in the operation of the aircraft.

I think Avbug clearly explained the ambiguity of the AC in question: it's a very convenient blanket.

Perhaps the latest technology does in fact prevent ice bridging. So what? What am I supposed to do when I'm flying a 20 year old turbo-prop with boots that I feel are inadequate?

Of course I always comply with all company policies, all AFM limitations, all FARs and OpSpecs. That goes without saying.

Here's what nobody ever told me: There are three factors that I consider before I blow the boots:

*Airspeed
*OAT
*General condition of the boot

Airspeed: All things being equal, the boot will do a better job at barber pole than it will at Vref.

OAT: All things being equal, the boot will do a better job in warmer temps.

Condition of the boot: Here's a two edged knife. If the mechanics have just applied the wax and it's real slippery the ice will just slide right off. The problem is that wax, over time, will deteriorate the condition of the rubber and eventually ruin the boot.

So, if I have anything to offer it's this:

Don't mess around in the ice--it kills. Always follow established procedures. Maintain good situational awareness--it may behoove you to wait until you have more ideal conditions to blow the boot. The PIC is the final authority in the operation of the aircraft.

Always fly the airplane.
 

1900laker

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1900s handle Ice very well!! Especially at lower altitudes, like ORD last winter. I remember one bad icing day in particular. The wings cleared well, but I was shocked at the amount of Ice that accumulated on the nose of that puppy. Handled very well throughout.
 

avbug

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Remember, too that it's not the ice you can see that should concern you, but the ice that you can't see. Perhaps the most insidious and hazardous buildup will be on the horizontal stab, and tailplane icing can be a bear. Recovery from tailplane icing in many aircraft requires a concious and deliberate thought process, because it goes against the grain of everything you've been taught to believe. In most cases, it requires a reduction in power, and it requires that the stick or yoke be brought aft during the stall, to effect recovery. Generally, a reduction in airspeed is in order.

you can't see the tail in most cases, or determine the status of the de-icing capability until performance degrades. In the case of the horizontal stab, often you're in a world of hurt if performance degrades to the point of giving an indication.

The airplane may fly well with a load of ice, but much like babies with a fever, things can turn south in a big hurry with little warning.
 
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