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De-Icing Information (Chemicals, Process, Etc.)  
User currently offlineANITIX87 From United States of America, joined Mar 2005, 3305 posts, RR: 13
Posted (5 years 6 months 2 weeks 4 days 22 hours ago) and read 9518 times:
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Hi, everyone.

Some questions that came to mind regarding the de-icing process done before flights...

1) What chemical(s) are used and why?

2) Are the chemicals hot to help melt any existing ice?

3) How long is a de-ice effective? Does it ever happen that an aircraft gets de-iced and then is delayed long enough to require another run? Or do they intentionally wait until they know it is going to leave?

4) Is de-icing usually done at the gate? Or do all airports have de-icing bays located near runways so that it can be done while an aircraft waits for its slot?

5) How long does it take to de-ice the following aircraft: CRJ-700, A320, 777, 747, A380?

6) What surfaces of a plane MUST be de-iced prior to flight? What surfaces are non-critical and can be overlooked if need be?

7) What weather conditions must exist for an aircraft to be de-iced?

TIS


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3 replies: All unread, jump to last
 
User currently offlineKingAir200 From United States of America, joined May 2006, 1619 posts, RR: 2
Reply 1, posted (5 years 6 months 2 weeks 4 days 18 hours ago) and read 9486 times:



Quoting ANITIX87 (Thread starter):
1) What chemical(s) are used and why?

Ethylene or propylene glycol. Propylene is preferred due to its nontoxic nature.

Quoting ANITIX87 (Thread starter):
2) Are the chemicals hot to help melt any existing ice?

Deicing fluid yes, anti-icing no.

Quoting ANITIX87 (Thread starter):
3) How long is a de-ice effective? Does it ever happen that an aircraft gets de-iced and then is delayed long enough to require another run? Or do they intentionally wait until they know it is going to leave?

Depends. Yes. Ideally.

Quoting ANITIX87 (Thread starter):
4) Is de-icing usually done at the gate? Or do all airports have de-icing bays located near runways so that it can be done while an aircraft waits for its slot?

Depends on the airport. Smaller ones will frequently spray at the gate, larger ones will have centralized pads.

Quoting ANITIX87 (Thread starter):
5) How long does it take to de-ice the following aircraft: CRJ-700, A320, 777, 747, A380?

It depends on which types of fluid need to be used, how much contaminants are on the aircraft, and the skill level of those spraying and driving.

Quoting ANITIX87 (Thread starter):
6) What surfaces of a plane MUST be de-iced prior to flight? What surfaces are non-critical and can be overlooked if need be?

Everything. If you see snow or ice on the airplane, it's gotta come off.



Hey Swifty
User currently offlineMrChips From Canada, joined Mar 2005, 932 posts, RR: 0
Reply 2, posted (5 years 6 months 2 weeks 4 days 16 hours ago) and read 9468 times:



Quoting ANITIX87 (Thread starter):
1) What chemical(s) are used and why?

As mentioned above, ethylene and propylene glycol are components of deicing fluid, along with other things such as thickening agents, corrosion inhibitors and dyes. It should be noted that many deicing fluids are designed to be mixed, in varying concentrations, with water.

There are four types of deicing fluid (three in common use) specified by the Society of Automotive Engineers (SAE); Type I fluid (dyed orange) is basically raw, unthickened glycol - very similar to automotive engine coolant, apart from the additives, that is. As it is unthickened, Type I fluid does not really provide much inhibition to icing at temperatures above about -25 Celsius, and is often used for initial deicing only, or for anti-ice protection at very low temperatures. Type II fluid (dyed yellow) is a thickened glycol mixture, and is designed to shear off the wings (due to aerodynamic forces) of an aircraft at speeds in excess of 100 knots. The thickness of Type II fluid makes it stick to surfaces, thus allowing longer holdover times. Type II is no longer in common use today, as it is extremely expensive and is quite toxic, from what I understand. Type III fluid (dyed yellow) is similar to Type II, but it is designed to shear off at speeds of less than 100 knots. Mostly, this fluid is used for anti-ice protection for regional aircraft and business jets. Type IV fluid (dyed green) is largely to the same specification as Type II fluid, but it is somewhat less expensive (and not nearly as toxic), and provides slightly longer holdover times.

It should be noted that the anti-icing fluids (Types II, III and IV) are only used if there is precipitation falling, as there is obviously no need for anti-icing fluids if it is clear out. Also, the cost of the anti-icing fluids is astronomical. To give you an idea how much the difference is, I was told several years ago that the cost of deicing a Boeing 737 with Type I fluid would be about $800 or so. Now, to deice with Type I and then apply a layer of Type IV to the same aircraft would cost about $8000. Needless to say, air operators use anti-icing fluids very sparingly.

Quoting ANITIX87 (Thread starter):
3) How long is a de-ice effective? Does it ever happen that an aircraft gets de-iced and then is delayed long enough to require another run? Or do they intentionally wait until they know it is going to leave?

All deicing fluids have holdover times, or HOTs. Basically, these times (found on tables published by the fluid manufacturer) indicate how long the fluid will protect against surface contamination, based on temperature, fluid concentration and the amount and type of precipitation falling. It should be noted that there is no holdover times exist for anything more than moderate freezing rain or heavy snow, even for Type IV anti-icing fluid.

Quoting ANITIX87 (Thread starter):
6) What surfaces of a plane MUST be de-iced prior to flight? What surfaces are non-critical and can be overlooked if need be?

"Critical surfaces" of an aircraft include the wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft and, in the case of an aircraft that has rear-mounted engines, includes the upper surface of its fuselage. It should be noted that section of the fuselage through which the wings pass is considered to be part of the wing, and is therefore considered to be a critical surface.

Of course, airlines will often have even more strict rules than the bare minimum set forth by the regulator - some airlines require there to be no contamination whatsoever on any surface of the aircraft, and nobody that I know of would allow accumulations of snow or ice to remain on any surface - with one exception. It is permissible to allow an aircraft to takeoff with frost or ice on the undersides of the wings, so long as it is the result of cold-soaked fuel, and the accumulation remains within the limits published by the aircraft manufacturer.

Quoting KingAir200 (Reply 1):

Everything. If you see snow or ice on the airplane, it's gotta come off.

Snow or ice, yes. Frost - not necessarily.



Time...to un-pimp...ze auto!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4007 posts, RR: 34
Reply 3, posted (5 years 6 months 2 weeks 4 days 11 hours ago) and read 9440 times:



Quoting MrChips (Reply 2):
Type II is no longer in common use today

Well about 4 years ago we went over to type IV, used it for a season but gave up. Although the holdover times are better we found it very difficult to apply a neat coat. So no we use type II for anticing.

Quoting KingAir200 (Reply 1):
Everything. If you see snow or ice on the airplane, it's gotta come off.

Yes to snow. But hoar frost on the fuselage, and frost under the wings is OK. Also when the snow is cold and dry and light we leave it on the fuselage as well. It all depends really.

Quoting ANITIX87 (Thread starter):
How long is a de-ice effective?

You have to distinguish two terms.
Deice and Antice.

If the plane is covered with frost or snow it is deiced. If there is active frost or precipitation then it is anticed afterwards. Or sometimes at the same time.
I have been involved with deicing for 20 years, at many different airports, and it is amazing how many different ways there are to get the plane ready.

We use two stage. If the aircraft is covered in snow then we start with an air blower, just blows the snow off. Very effective near cockpit windows. Then we deice with Type 1 fluid at a mix of around 50%, but can be less when the OAT is above zero. Then if it is snowing we antice with Type II at 100%. The type I is applied at 80degC, the type 11 is cold.
Nearly all deicing at the gate.

Same airline, different airport, use only Type II, but deice with type II at 50% or lower. Reason is they have many planes to treat, and not enough trucks. So they can start early in the morning and have longer holdover times.

Next airport, only use type I, but deice on pads at each runway threshold, with engines running, so aircraft takes off immediately. If you can take off in 10 mins after treatment, then type I can be enough. We need Type II because of the take off queue.

There is more than one way to skin a cat.

Quoting ANITIX87 (Thread starter):
How long does it take to de-ice the following aircraft: CRJ-700, A320, 777, 747, A380?

Depends. With two trucks and only frost on the aircraft 2-5 mins.
With overnight snow that has frozen on, over 40 mins.

I once had a B744 in a snowstorm. Two trucks would not cope. When they had finished, they had to start again. So we used four trucks and even then it wasn't good when it taxied out.


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