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ScoobySnacks
2nd Feb 2002, 01:41
I was recently "One-Step" deiced with Type I Porpylene fluid, other Types were inoperative. Wing fuel temperature was -20C, OAT was -10C with light snow. We estimated our holdover to be 12-15. We had some discussion about the effectiveness of Type I on a cold soaked wing and decided to do a Pre-Takeoff Contamination Check from the Cabin. Everything looked OK, so we launched.

Question: I'm curious to know if any of you have experienced, or have heard on instances where Type I fluid has frozen on a cold soaked wing? I understand Type I has some Propylene in it, but the mix is mostly hot WATER!

pigboat
2nd Feb 2002, 05:32
I don't mean to question your judgement, but why get de-iced at -10?

ScoobySnacks
2nd Feb 2002, 06:56
I thought, perhaps, it was implicit.

You show up to preflight an airplane that's previously been airborne for 5 hours. It's covered with snow and it's still snowing. OAT is -10, the wing fuel is -20, so....you deice/anti-ice. My concern is that spraying Type I fluid on such a wing may quickly reach the fluid's freeze point. Not unlike a Zamboni Machine for you hockey fans.

. .I'll restate my question..........

Has anyone experienced Type I fuild freezing on a cold soaked wing?

320DRIVER
2nd Feb 2002, 09:17
Scooby Snacks, according to the latest issue of AEA Recommendations for De-icing/Anti-icing of Aircraft on the Ground, Edition 15, September 2001, it appears that the holdover time after a Type I de-ice/anti-ice, one-step procedure is 6 minutes for light snow to 3 minutes in moderate snow.

There is a note in the holdover time table stating that these limits may be further reduced when the aircraft skin temperature is lower than OAT as in your case.

I believe these tables have been revised in this new issue and in fact Type I fluid is now almost exclusively used as a de-icing fluid since the holdover times for anti-ice purposes are not practical any longer.

[ 02 February 2002: Message edited by: 320DRIVER ]</p>

pigboat
2nd Feb 2002, 09:58
Scooby I'm sorry if I sounded flippant, I had no wish to do so. Your second post states that the aircraft had flown for 5 hours previously, thus it was cold soaked. At an OAT of -10, snow will not stick to the surface. The problem I'd have with de-icing the aircraft as opposed to sweeping the snow off or just letting it blow off on takeoff, is that by wetting down the wing you provide an excellent base for the falling snow to stick to. This would create a contamination problem where none existed before.. .I don't have the tables in front of me, but the holdover time for Type 1 fluid by itself is very short. Under the conditions you describe, if you must de-ice, Type 1 at a temperature of 110-120*F should be used to de-ice, followed by an application of Type 4.

Basil
3rd Feb 2002, 22:01
Just in case any newcomers to the profession are in any doubt ref airframe contamination:. .1. If there is ANY contamination whatsoever on the upper surface of the wings it MUST be removed. Do not depend upon snow blowing off. Snow may drop into gap between tailplane and elevator and cause restriction of movement esp if curtained.. .2. If the holdover time of the de-icer is insufficient then DEMAND appropriate anticing. If not available request hotel rooms for pax & crew hinting that airline will sue airport authority for cost thereoff. <img src="wink.gif" border="0"> . .3. Frost from cold-soaked wings is not acceptable on upper surface. Unfortunately, this may occur when tankering fuel into airports which rarely suffer from snow/ice and therefore have no de-icing equipment. Try (before re-fuelling) pumping wing fuel into centre tank and then re-fuel wings with warm fuel or run booster pumps to warm-up fuel; bit of a long process with several tonnes of paraffin at -10 deg on board.. .4. Finally - don't let tw^t climb up and try to warm up six tonnes of fuel by chucking bucket of hot water over wing! <img src="mad.gif" border="0">