In SYR, I have be deiced on many an occasion, in many different conditions, but I've always forgotten to ask why they have different procedures at different times? I understand that in only slight freezing conditions with low precipitation, you're only doing critical parts of the plane out of an abundance of caution, but what is the virtue of deicing all parts of the plane when it is not freezing rain/blizzard?

https://www.airliners.net/photo/Cayman-Airways/Boeing-737-3Q8/2577265/

All moving parts, wings, stabilizers, rudder, and any probes, but what benefit does it serve to use barrels of expensive fluid doing the fuselage from door to door?

The clue is in the picture title. It was a snowy morning. The aircraft had probably been parked overnight and was covered in snow. Although frost on the fuselage is OK, Snow is not and has to be removed.

Weight has to be a factor -- it's not clear on the attached picture specifically, but in general you don't want any significant extra weight.

What does the snow on the fuselage do? Assuming it is not piles of it.

Under certain conditions clear ice will form on a fuselage and it's hard to tell. The other issue is that aircraft "cold soak" and will start to have ice form way about the freezing point of air.

Clear ice on the wings and fuselage can be very dangerous to systems especially engines on the T-tails when it breaks off usually during the rotation or first few minutes of flight.

Some aircraft are also very sensitive to buildup on the fuselage, regional aircraft come to mind.

That makes sense. Thank you for the detailed description.

Quoting Cosyr (Reply 3): What does the snow on the fuselage do? Assuming it is not piles of it.

Melts and then refreezes, especially *under* the snow where you can't see it. As the fuselage warms up, the snow in contact with the slightly warmer skin can melt, while the snow above it stays snow. If the weather changes by a degree, that melted snow can refreeze and stick to the fuselage. It can look like a little fluffy snow on the fuselage that'll blow off, but underneath can be a sheet of bumpy ice.

IIRC, this is one of the things that happened to Air Florida flight 90. Basically anything bad that can happen, icing-wise, did happen to that flight. Engine icing, wing icing, fuselage icing, and all of it had some effect on the performance and aerodynamics of the plane. And they only needed a tiny bit more of both to make it.

Quoting durangomac (Reply 4): Clear ice on the wings and fuselage can be very dangerous to systems especially engines on the T-tails when it breaks off usually during the rotation or first few minutes of flight.

Inadequate de-icing resulted in this SAS MD-81 ingesting clear ice into both engines, causing severe damage, soon after takeoff from ARN in December 1991. Fortunately no fatalities.
http://aviation-safety.net/database/record.php?id=19911227-0

The caption on that photo is actually wrong (so is the use of Type IV on the entire aircraft..). Type IV is ANTI-icing, not DE-icing.

The proper procedure is type I (DE-icing fluid, orange with consistency of water, heated) anywhere on the aircraft where there are contaminants, including under the wings and control surfaces. If there is precipitation at the departure airport, Type IV (ANTI-icing fluid, green with motor oil consistency, cold) will be applied to the top of wings and tail only (some aircraft have exceptions) after Type I is completed. Type IV will then shear off during takeoff taking with it any contaminants that have fallen since it was applied. It allows for a longer taxi time (known as holdover time).

Quoting KaiGywer (Reply 8): The caption on that photo is actually wrong (so is the use of Type IV on the entire aircraft..). Type IV is ANTI-icing, not DE-icing.

Maybe where you live but not everywhere. At LHR BA only use type IV fluid. They dilute it to different concentrations and use it for deicing and anticing.
No need to apply Type IV for anticing if deicing is carried out at the remote area...

Oslo airport tried infrared heating for deicing. It worked but cost too much.
There is no proper procedure, only the proper result, which is a clean wing for takeoff.

Can you imagine de-icing an A380? Holy Cow, that would take a while.....

Good Morning all,

I am a deicer in Canada and i deal with both US carriers and Canadian Carriers and the reason that deice is done has all ready been discussed. But there are regulations in the US that are mandated by the FAA that state the aircraft has to be clean of all contaminants (snow, frost, ice, ect...) and for that reason that is why US aircraft and flights coming out of the US have to follow FAA guidelines and be clear of all contaminants. In Canada they are regulated by CARs and its 6.02.11. that states "an aircraft can not take off with any contamination adhering to the control surfaces of the aircraft" (readers digest version). As well the FAA has implemented that once an aircraft has received it's final application any reconfiguration of the air craft IE. for take off they lose 10% of the hold over time because it exposes non treated areas of the wing. As for clear ice there has been a few crashes that were caused by it SAS is one of them the other one that comes to mind is air Ontario in Dryden ont. As for the question about the fuselage being deiced it is the PIC's call and also if the deicers notice contamination on the fuselage that is thicker than permissible amounts. As for the picture if they have a long taxi time and they are worried about contamination ADHERING to the fuselage than that is why the full bath of type IV. Tristarsteve i think you may have a typo but i could be incorrect but i believe at LHR they use type II or type III as it provides a greater hold over time than type I. The main thing to remember when it comes to deicing is the word adhering because if it's not than you are able to take off with out deice if there is nothing underneath (which is usually never the case). Hope y'all have safe travels and if you get deiced say thank you to those guys they freeze and get covered in glycol so that you can get to your destination safely.

Cheers.

Like others have said, hoar frost is permitted under certain conditions. However, snow and ice must be removed.

Type IV is to protect the surfaces from accumulating frozen precipitation during holding and taxi times and sluffs off during takeoff.

Now, there is another factor to consider. The image in question is a Cayman Airways plane. The Caymans are in the topics. I learned when I moved from Michigan to Florida, there is a huge difference in pilots that fly the north all winter long and those that only get up there occasionally, called southern pilots. Southern pilots tend to want a lot more de/anti-icing done than northern pilots. A southern pilot will call for the entire plane to be de-iced for a little hoar frost, whereas the northern pilot, much more used to icing conditions on the ground, may deny the need or go for only wings and tail.

I find no fault in either mentality because its their butt on the line in both responsibly and actual life or death. So, even when I thought it would be OK to go, if the Captain said spray us, I sprayed. That amount of de/anti-icing fluid is a small insurance policy for the lives onboard that aircraft. Although, if the Captain not to spray and as a trained individual, I thought it should be, I'd express my disagreement on the flight deck and if s/he still insisted, I'd let them go. But I'd make sure that the Cockpit voice recorder documented the conversation so I was covered for liability if a mishap occurred.

[Edited 2015-05-01 12:31:04]