De/anti-icing HOT TYPE I?

[Studsgaard]

Quick question.
Your aircraft has been parked up for some time and is now covered with ice and snow. It's a clear day with freezing temperatures but above dew point.
So after de-icing with type I you strictly don't need anti-ice since you are not in icing conditions. But at some point your type I will start freezing I guess. The only HOT I can find that comes closest is for 'active frost'. But for this condition your outside temp has to be below the dew point.

Any suggestions?

[B737900er]

Type I Is used for De-icing, and seeing as there is no active weather phenomenon about, I don't see why you need to add anti-ice.

You should be setting off after De-icing anyway, so there won't be enough time for it to re-freeze unless its extremely cold.

PS. Type1 will include some alcohol/chemical to stop it from re-freezing

[Tu.114]

There should be tables available from Your company giving You minimum temperatures for the relevant mixture ratios for deicing and antiicing respectively. For deicing, typically a thinner mixture is allowed, as the fluid is replaced with a thicker liquid in the second step within 3 minutes; the anti-icing table will allow for longer time on the wing before departure.

What is wrong with using the "active frost" HOTs to determine the time between deicing and takeoff when there is no actual frost accumulation expected? During this HOT, You are not only protected against frost, but the liquid will retain its properties as well if no additional water is joining it. So I would see no problem in using the most "lenient" tables available while You have definitely no worse weather than what is covered by them.

[Mad (Flt) Scientist]

The thing you should be referring to is the LOUT - Lowest Operational Use Temperature - for the specific fluid. Basically, it gives you a margin to the freezing point of the fluid.

Which means as long as you are above the LOUT, the fluid simply will NEVER freeze.

Still no reason to wait around, but in principle you could wait all day, as long as there's no active precip and you are above the LOUT.

below the LOUT, you shouldn't be spraying the fluid at all, as there;'s a risk it will indeed freeze.

[Miles Magister]

Type I should be applied at a mixture which has a freezing point at least 10deg C below the ambient temperature so you should be safe. The warm water melts the frost then the Type I prevents refreezing, even when it has cooled down.

If you PM me I can probably find the tables for mixture strength against freezing temperatures for the most commonly used Type I, Kilfrost.

So even with no hold over time, if there is no active frost then you can wait as long as you like and you will probably still be safe. Just make sure you do a tactile (touch the wing with your hand) inspection before departure. Basically assume that Type I does not have a hold over time. Hold over times only apply to active icing conditions.

Details of the procedure can be found in the Association of European Airlines recommendations, which is the recognised authority document on the subject.http://www.aea.be/news-media-room-media-centre/publications/9-recommendations-for-de-icing-anti-icing-of-aircraft-on-the-ground.html

[Mad (Flt) Scientist]

I see Studsgaard is listed as being in Denmark, so that AEA link is probably the best option. (I still find it odd that EASAland relies on an industry group alone for something this important, but that's another discussion ...)

Alternative references for North America would be:

FAA
HOTs: http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/media/faa_2014-15_holdovertables.pdf
Guidance (AC120-60B: AC 120-60B - Ground Deicing and Anti-icing Program ? Document Information (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/23199))

Transport Canada
HOTs: Holdover Time (HOT) Guidelines - Transport Canada (http://www.tc.gc.ca/eng/civilaviation/standards/commerce-holdovertime-menu-1877.htm) (also has a link for 14052 here too)
Guidance (TP14052: TP 14052 - Guidelines for Aircraft Ground - Icing Operations - Transport Canada (http://www.tc.gc.ca/eng/civilaviation/publications/tp14052-menu-314.htm) and TP10643: TP 10643 - When in Doubt... - Transport Canada (http://www.tc.gc.ca/eng/civilaviation/publications/tp10643-menu-1118.htm))

Table 10 of the TCCA HOT paper gives LOUTs for a sange of fluids. (Starts on page 53)

[Studsgaard]

Thanks guys.
I've got all the tables and read the documents you are referring to, but since there is no published HOT for these conditions I was curious to hear your thoughts.

I am in biz jets and it would be practical to de-ice before the pax arrives but sometimes you end up waiting forever….

I guess the alcohol would evaporate at some point and I am not sure I would wait all day.

[Mad (Flt) Scientist]

If there is no precipitation then there is, as you say no defined HOT. Which means its infinite.

Think about it, if you sprayed in the middle of summer, you could wait forever and nothing could happen (well, eventually the fluid would evaporate, and you'd have wasted a few grand, but that's all)

Provided it's above the LOUT and you have the temp margins MM mentions, the fluid is perfectly safe on the wing. No matter how long you wait.

HOT is about how long the fluid will protect against re-contamination, not about how long the fluid can stay on the wing with no contam present.


The only cautionary remarks I'd make about pre-emptive de-icing is that if you leave the thickened fluids on too long, then the "carrier" fluid evaporates, the thickening agents remain, and THEY can cause a problem. (Rehydration of residues has been a problem for some in the past). I'm only aware of that in cases where Type II or IV was allowed to totally dry out overnight.

The other gotcha for pre-emptive de-icing is that any HOT you are using starts at application - not at exposure to the elements. Again, some people have anti-iced in a hanger, intending to be towed out later and start the "HOT timer" once they are outside. That's not legit, as the fluid is flowing off all the time (especially if the hangar is warm as well). So you don't start with the right thickness on the wings. (It'll also make a mess of the floor, too...)