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SEA Deicing Question  
User currently offlineEIPremier From United States of America, joined Sep 2000, 1550 posts, RR: 1
Posted (2 years 12 months 16 hours ago) and read 2112 times:


Just observed something at SEA today which struck me as curious, and was wondering if the tech/ops community had any insight. I was waiting at the C concourse around 11 am today (2/17), and I saw two planes being deiced at the gate prior to pushback. One was a 739 going to SJD and the other was a 738 going to GEG. The odd thing was both aircraft had come in from other cities, so they weren't RON aircraft. Furthermore, the outside temp was way above freezing (44 deg F according to wunderground), and the cloud deck was low, but no precip since the prev evening. Not that I'm questioning their decision to de-ice, but I just couldn't really figure out why it was needed. Anyone have any insight?

3 replies: All unread, jump to last
User currently offlineokie From United States of America, joined Jul 2003, 3670 posts, RR: 3
Reply 1, posted (2 years 12 months 15 hours ago) and read 2097 times:

Quoting EIPremier (Thread starter):
The odd thing was both aircraft had come in from other cities, so they weren't RON aircraft. Furthermore, the outside temp was way above freezing (44 deg F according to wunderground),

There is your clue. They flew in from an altitude that was -44F and had cold soaked the plane, wings in particular.
With thousands of pounds of Aluminum and Fuel cold soaked to -44F then when sitting on the ramp the wing started to form frost.
I can not count the times that I have waited for de-icing on an aircraft but I would say 70% of the time was in conditions that you mentioned 40-45F and humid, night or cloudy.


User currently offlineRoseflyer From United States of America, joined exactly 12 years ago today! , 10927 posts, RR: 52
Reply 2, posted (2 years 12 months 13 hours ago) and read 2023 times:

The airplane is extremely cold when landing. When there is high humidity, moisture condenses on the plane and then freezes which foreces the plane to deice.

If you have never designed an airplane part before, let the real designers do the work!
User currently offlineMrCazzy From United States of America, joined Oct 2011, 35 posts, RR: 0
Reply 3, posted (2 years 12 months ago) and read 1923 times:

agree with okie, when flying at high altitudes it is considerably colder than on the ground, if there were any precip, clouds at those altitudes there could easily be freezing

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